See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/270279245 Raman Study on Pompeii Potteries: The Role of Calcium Hydroxide on the Surface Treatment ARTICLE in JOURNAL OF SPECTROSCOPY · DECEMBER 2014 Impact Factor: 0.54 · DOI: 10.1155/2014/435026 CITATION 1 READS 49 6 AUTHORS, INCLUDING: Daniele Chiriu Università degli studi di Cagliari 29 PUBLICATIONS 107 CITATIONS SEE PROFILE P.C. Ricci Università degli studi di Cagliari 104 PUBLICATIONS 751 CITATIONS SEE PROFILE Andrea Polcaro Università degli Studi di Perugia 40 PUBLICATIONS 11 CITATIONS SEE PROFILE Davide Nadali Sapienza University of Rome 36 PUBLICATIONS 8 CITATIONS SEE PROFILE All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately. Available from: Daniele Chiriu Retrieved on: 03 February 2016
Research ArticleRaman Study on Pompeii Potteries The Role of CalciumHydroxide on the Surface Treatment
Daniele Chiriu1 Pier Carlo Ricci1 Andrea Polcaro2 Paolo Braconi2
David Lanzi2 and Davide Nadali3
1Dipartimento di Fisica Universita di Cagliari sp n 8 Km 0700 Monserrato 09042 Cagliari Italy2Dipartimento di Lettere-Lingue Letterature e Civiltarsquo Antiche E Moderne Universita di Perugia Via Armonica 306123 Perugia Italy3Dipartimento di Scienze dellrsquoAntichita Sapienza Universita di Roma Via dei Volsci 122 00185 Roma Italy
Correspondence should be addressed to Pier Carlo Ricci carloriccidsfunicait
Received 28 October 2014 Accepted 17 December 2014 Published 31 December 2014
Academic Editor Petre Makreski
Copyright copy 2014 Daniele Chiriu et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
Pottery samples from the Pompeii archaeological site were investigated by IR Raman spectroscopy and EDAX measurements Theanalysis of the Raman spectra of the surfaces reveals the presence calcium hydroxide (peak at about 780 cmminus1) while the calciumcarbonate is totally absent The comparative studies on the carbonation effect of the surfaces were performed on laboratory grownsamples of calcium hydroxide The samples were treated at high temperature and exposed to different ambient conditions and theanalysis suggests that the original surfaces of Roman pottery were scattered by calcium hydroxide (limewash) before the cookingprocess in the furnaceThe result of this surface treatment not only permits a vitrification of the surfaces but also seems to reduce thecontent of CO
2
in the furnace atmosphere and then obtain a more oxidant ambient during the cooking of the potteryThese resultsgive new insights on the real degree of knowledge of the Romans about the art of ceramics andmore generally about chemistry andtechnologies
1 Introduction
Nowadays the use of technological experimental techniquesin the field of cultural heritage is widely accepted anddiffused The amount of information that a joint approachbetween physics chemistry and archeology is sensiblyincreased and the efforts in this direction are always growingThe problem that is emerging with the diffusion of tech-nologies is the needed of ldquopurerdquo sample intending the studyof samples that were not altered after their recovery Thistrivial consideration increases its importance when we aredealing with samples that were found decades or centuriesago when the treatment for restoration was not so accurateand they were not deeply studied with particular regard totheir influence on the same samples with time In this senseone example is the use of Paraloid Paraloid is an acrylicresin which used a stabilizing of the samples that intensify thecolors and the brilliance of the surfaces and at the same time
decreases the effect of environmental at the surface Howeverthe use of Paraloid in some sense decreases the possibilitiesto perform further analysis on the treated samples In thissense the use of untreated samples ismandatory to gather newinformation in cultural heritage in particular in well-knownarchaeological excavations [1 2]
This paper displays the results of studies on differentsamples founded during the excavations guided by Peru-giarsquos University among 2004 and 2008 for the ldquoRegio VIrdquoproject (Figure 1) in the framework of the project ldquotimethrough colorsrdquo funded by the Italian Ministry of Universityand Scientific Research within the national grant ldquoFuturoin Ricercardquo 2012 Studies on productionrsquos scraps come toknow some technical details related to the so-called ldquoPro-ductionrsquos Archaeologyrdquo These technical details specificallyconcern the heat treatmentrsquos temperature of ceramic waresthe composition of clay the type of coating and the typeof ambient generated during the heat treatment (oxidative
Hindawi Publishing CorporationJournal of SpectroscopyVolume 2014 Article ID 435026 10 pageshttpdxdoiorg1011552014435026
2 Journal of Spectroscopy
Figure 1 Comprehensive view of the archaeological site of Pompeii(Region VI)
Figure 2 Furnace situated below the triclinium of domus VII 159-10
or reductive) Part of the samples consists of productionrsquosscraps of two manufacturing centres now located below thefoundations of domusVI 5 9ndash19 and domusVII 15 9-10Theother part consists instead of plasters founded in differentstratigraphical units of domus VII 15 1-2 also known asldquoCasa del Marinaiordquo
During the 2004 excavations a furnace was found amongthe foundations of domus VI 5 9ndash19 (furnace VI) This fur-nace was built with a twin praefurnium and a quadrangularcombustion roomThis manufacturing centre dates back to aperiod between the end of the IIIrd century bC and the halfof the IInd century bC as evidenced by productionrsquos scrapsThe production consists mainly of dolia large containerssome kinds of ldquoollardquo in common ware and pans in internalred slip ware
The furnace situated below the triclinium of domus VII15 9-10 (furnace VII) produced instead amphora cookingware common ware and internal red slip ware (cumanaetestae) All the samples can be dated at the beginning of theIInd century bC (Figure 2)
Studies on plasters take moves to verify the chemical andphysical transformations caused by the thermal shock due toVesuviursquos eruption of 79 AD Plasters were founded in 2007on a trench inside the second atrium (amb I) of the so-calledldquoCasa del Marinaiordquo
In this paper we report the Raman spectra the vibra-tional analysis and the EDAX measurements on the abovementioned archeological samples and for comparison withsamples grown and treated specifically in laboratory
Being applied in archaeology only in the recent yearsRaman spectroscopy is becoming increasingly important
as an analytical tool in conservation science [17 18] Itsrelevance is given by the intrinsic properties of the techniqueactually Raman spectra are obtained by excitation with lowenergy radiation by contrast with common ldquoarchaeologyrdquoexperimental techniques such as Mossbauer spectroscopyand Electronic Spin Resonance Raman spectroscopy is com-pletely not destructive and does not need any pretreatmentof the samples Moreover thanks to the advances in thetechnology devices in the recent years it is possible to collectexcellent experimental data in situ by means of opticalfiber coupled devices with small and compact dispersiveapparatusThepossibilities to utilize an excitationwavelengthat 1064 nm and collect an efficient Raman signal are of partic-ular relevance in untreated samples where the luminescencesignal often overlaps and masks the weak Raman signals
A deep scientific study by means of nondestructive andtechnologically advanced techniques on untreated potterysamples from the archeological excavation of Pompeii cangive new light on the pottery manufacturing methods ofRomans and more in general about the art of ceramics inRomanrsquos age
2 Materials and Methods
Raman scattering measurements were carried out in backscattering geometry with the 1064 nm line of an NdYAGlaser Measurements were performed in air at room tem-perature with a compact spectrometer BWTEK i-RamanEx integrated system with a spectral resolution of about9 cmminus1 Chemical analysis was carried out by using EDAXmicroanalysis system of a Dual Beam FEI Nova
Different samples originating to mention two furnaces(furnace VI and Furnace VII) in Pompeii were analyzed Forsake of clarity and brevity we choose as representative ofthe different samples the fragments denoted by VII59B11 andVI59B7Z for the furnaces VII and VI respectively (Figures3(a) and 3(b)) However if it is not explicitly indicated nodifferences in the measurements performed were observedwith respect to other samples with the same provenienceor inside the same sample itself Moreover the sample659A14730 (Figure 3(c)) a clear waste of production wasused as comparative sample
Raman analysis interested also two different plasterrsquossamples
(i) the first sample (sample HT) was a IVth style paintingexposed to the heat of the eruption This sample wasoriginally situated on the US 1 at 35003 meters asl
(ii) the second sample (sample LT) was instead a Ist stylepainting dated to the IIIrd century bC and notexposed to the heat of the eruption This sample wasin fact situated on the US 22 at 33803ndash33863 metersasl and was covered by 14 meters of ground duringthe eruption
3 Experimental Results
The internal and external faces of the VI 59B7Z samplewere analyzed byRaman spectroscopy EDAXmeasurements
Journal of Spectroscopy 3
(a) (b) (c)
Figure 3 Images of the samples VII59B11 (a) VI59B7Z (b) and 659A14730 (c)
450 300
1200 1000 800 600 400
ExternalInternal
VI59B7Z
Inte
nsity
(au
)
Raman shift (cmminus1)
(a)
450600
1200 1000 800 600 400
ExternalInternal
Inte
nsity
(au
)
A A AR R
Raman shift (cmminus1)
(b)
Figure 4 Raman spectra of the external and internal surface of samples VI59B7Z (a) and VII59B11The inset in the (a) section is an enlargedview of the external surfaces of sample VI59B7Z The inset in the (b) section reports the Raman spectrum form the cross section of sampleVII59B11 The peaks are identified as TiO
2
in the anatase (indicated with A) and rutile phase (R)
and SEM images the Raman Figure 4(a) reports the Ramanspectra a large band between 600 and 900 cmminus1 centered atabout 780 cmminus1 is present in both the spectra and no otherpeaks are easily distinguishable in the spectrum relative tointernal surface On the contrary the Raman spectrum ofthe red external surface of the sample VI 59B7Z present alsopeaks at 226 292 and 411 cmminus1 assignable to the hematitephase of the iron oxide (inset Figure 4(a)) [19] Actually theuse of iron oxides in different polymorph as red pigmentsis widely stated [18 20 21] The Romans achieved differentcolours from deep red to purple through the grinding ofhematite crystals The particle size affects the colour wherevery fine particles on a nanometer scale gave purple
According to [22 23] the large peaks at 780 cmminus1 can beassigned to the presence of calcium oxide and calcium hydrox-ideAs a confirmation the EDAXanalysis (Figure 5)was takenalong the different surfaces the peaks of calcium and Ironare well evident several elements have also been detected inthe samples probably arising from natural minerals presentin the proximity of the excavation site such as quartz (SiO
2
)feldspars leucite (KAlSi
2
O6
) and kaolinite (Al2
Si2
O5
(OH)4
)[24 25]
To better observe differences between the clay and thesurface of the pottery the samples were analyzed also inthe cracks of the surfaces and in cross section the Ramanspectrum does not reveal any presence of calcium hydroxideand the EDAX analysis reveals a small and reduced presenceof calcium while the relative presence of different elementsremains almost unaltered (Table 1)
In the sample VII59B11 (furnace VII) the Raman spectrataken along the cross section randomly present peaks at395 450 517 and 635 cmminus1 (see inset in Figure 4(b)) Threeof them are easily assignable to the presence of TiO
2
inthe anatase phase while the peak at 450 cmminus1 and theenlargement of the band at 635 cmminus1 suggest the presenceof TiO
2
in the rutile phase [26 27] It is worth noting thatthese elements are present only as tracewith respect to jumbleand the relative high intensity of the Raman signal is dueto the high efficiency of these materials and phases [26 27]In most of the other samples these peaks were not observedsuggesting the random presence of titanium oxide in thestarting material Again the Raman signal arising from thesurfaces is dominated by the large by assigned to the presenceof calcium oxidehydroxide (Figure 4(b))
4 Journal of Spectroscopy
Table 1
(a)
Element Wt At 119870-ratio 119885 119860 119865
C K 1599 2876 00481 10720 02805 10005O K 3812 5146 00780 10531 01943 10003Mg K 123 109 00053 10085 04310 10012Al K 160 128 00088 09784 05614 10019Si K 304 234 00208 10079 06754 10019K K 037 020 00032 09572 08983 10257Ca K 1809 975 01643 09789 09245 10034Fe K 1015 392 00886 08913 09776 10024Pb L 1141 119 00719 09181 10189 10000Total 10000 10000
(b)
Element Wt At 119870-ratio 119885 119860 119865
C K 1526 2515 00331 10540 02058 10004O K 4131 5110 01138 10355 02661 10003Mg K 150 122 00082 09920 05523 10044Al K 683 501 00448 09625 06778 10055Si K 1460 1029 01061 09900 07328 10011K K 209 106 00183 09395 09214 10117Ca K 705 348 00638 09608 09391 10027Fe K 619 219 00537 08717 09939 10017Pb L 516 049 00315 05993 10185 10000Total 10000 10000
C
Ca
Si
MgFe
Fe
K
AlPb
O
200 400 600 800
(a)
C
Ca
Si
MgFe Fe
K
Al
Pb
O
200 400 600 800
(b)
Figure 5 EDAX spectra from VI59B7Z sample taken on the surface (a) and cross section (b)
Journal of Spectroscopy 5
4 Discussion
The presence of the calcium oxide and hydroxide on theinternal and external surfaces of the samples as well as thecontemporary absence in the analysis of the cross sectionsand in the cracks strongly suggests that the calciumhydroxidewas not accidental on the surface but on the contrary it wasspread intentionally over both the surfaces of the potteries
On the other hand the use of limewash as binder of differ-ent pigments is widely proved and accepted in antiquities andin particular in ancient Roman walls [21 28 29] Accordingto Vitruvius intonaco is a set of finishing layers composedof lime and very fine-grained sand In this technique thecalcareous rock (mainly constituted by calcium carbonate(CaCO
3
)) is first selected in base to their purity (smallimpurity can vary the final color of the powder) then washeated in oven at high temperature (more than 1000∘C) Inthese conditions the calcium carbonate degrades in calciumoxide and carbon dioxide [21]
CaCO3(S) + heat 997888rarr CaO
(S) + CO2(G) (1)
Then the calcium oxide was mixed with water formingcalcium hydroxide
CaO3(S) +H2O 997888rarr Ca (OH)
2
(2)
Finally this compound (calcium oxidehydroxide) wasmixed again with calcium carbonate to obtain the so-calledintonaco that was applied to the wall in order to obtaina smooth polished surface that resembles marble To thiscompound often mineral pigments were added to formdifferent color on the wall Different works based on Ramanspectroscopy reveal the ill resolved double at 710ndash790 cmminus1due to the calcium oxidehydroxide plus a narrow band at1085 cmminus1 from the calcium carbonate
Some general and additional information can be deducedfrom the study of the Raman spectra of the intonaco actuallythe presence of the band from calcium carbonate is a clearindication that the samples were treated at high temperatureactually as previously stated at high temperature (above550∘C) calcium carbonate passes in calcium oxide (plusgaseous CO
2
) that being highly hygroscopic forms naturallythe calcium oxidehydroxide (CaO(OH)) In general whenthe samples were treated at relative low temperature boththe Raman signals from calcium carbonate and calciumoxidehydroxide are present as in the case of Roman muralpaints being the mural paint not thermal treated On thecontrary in our samples the absence of the band of carbonateas reported in Figures 4(a) and 4(b) can be used as anindication of a thermal treatment of the pottery samples athigh temperature
An interesting proof of the above mentioned heat effectis evident in the Raman spectra of the mural samples (casadel marinaio) Both of them refer to mural paintings fromPompeii but only the first of them (sampleHT)was in contactwith the high temperature generated by Vesuviusrsquos eruptionand the Raman signal from this sample does not presentthe peak at 1085 cmminus1 while the second sample (sample LT)pertains to a wall that was about three meters under the
Raman shift (cmminus1)
Inte
nsity
(au
)
1086 cmminus1
1200 1150 1100 1050 1000
Not exposed to eruptionExposed to eruption
Figure 6 Raman spectra taken on mural samples from casadel marinaio (Pompeii) exposed and not exposed to Vesuviusrsquoseruption The band position relative to the strongest Raman bandfrom the calcium carbonate is evidenced
ground level at the time of the eruption so the temperaturewas much lower and the calcium carbonate over the muralpainting was preserved (Figure 6)
On the contrary in the pottery samples from Pompeii(see the spectra from the VII59B11 VI 59B7Z samples asrepresentative in Figure 4) the band at 1085 cmminus1 is alwaysabsent in all the measurements performed suggesting thatthe limewash was spread over the pottery before the heattreatment in the furnace As further indication of this hypoth-esiswe report theRaman spectrumof the sample 659 A14730a clear waste of production (Figure 7) Again the band at780 cmminus1 is evident while the band of calcium carbonate isabsentThe spectrum of the jumble registered in cross sectiondoes not reveal any peak of this phase suggesting again thatthe limewash (calcium oxidehydroxide) was spread over thesurface before the heating treatment
It can be interesting to try to answer the question whichis the function of the calcium oxidehydroxide and why itwas spread over the surface of the pottery before the heattreatment
One hypothesis can be related to the same reason of themural painting that is to smooth the surfaces and to use theintonaco as a binder of the inorganic pigment (that need athermal treatment)
A secondhypothesis can be associated to an improvementto the normal cooking process of the pottery Actually theaddition of calcium oxidehydroxide creates a layer overthe surfaces that during the heat treatment remains highlyoxygenatedThe oxygen preserves the surfaces from carbona-ceous waste that blacken the final good moreover the oxygenpermits to obtain a relative higher temperature at the surfacesfavoring the vitrification process of the aluminosilicates
6 Journal of Spectroscopy
Raman shift (cmminus1)
1400 1200 1000 800 600 400
Cross sectionExternal
659 A14730
Inte
nsity
(au
)
Figure 7 Raman spectrumof the sample 659A14730 a clearwaste ofproduction of the furnace VII taken along the internal and externalsurfaces
the hardening of the clay and decreasing the porosity of thesurfaces [30 31]
The high oxygenated ambient of these samples is indi-rectly suggested from the presence of TiO
2
in the anataseforms Actually at temperature higher than 600∘C theanatase phase naturally transforms to the more stable rutilephase however highly oxygenated environmental conditionsincrease the temperature threshold for the phase transforma-tion up to 1000∘C [26]
As experimental proof of the thesis just illustrated withthe help of deconvolutions with lorentzian profiles it ispossible to analyze the Raman spectra in order to identify adegree of carbonation of the samples and then deep inside tothe absorption process of CO
2
during the heat treatment ofthe pottery and justify the use of calcium hydroxide as getterof the carbon dioxide produced during the heat treatmentAs indicated in [32 33] the method of the carbonic dioxidesequestration (CDS) is well kwon and used especially inthe case of the mineral carbonation of calcined calciumhydroxide (limewash) as indicated in the reaction
Ca (OH)2(S) + CO2 997888rarr CaCO
3(S) +H2O (3)
In the case of heat treated pottery thementioned reactiontakes place during the cooling process when the formationof calcium carbonate is allowed Calcium carbonate canassume different crystalline phases as indicated by [11 34]The principal structures are indicated in Table 2 with Ramanband and assignations
Moreover if the time of cooling is too fast it is possible tofind a mixture of mentioned phases with an high probabilityto obtain the compound in amorphous conditions [12 33 35]
The deconvolution illustrates the effective position ofthe experimental Raman bands in the spectra collectedon the ancient potteries (Figure 8 reports as example
the deconvolution from the sample 659 A14730 waste of pro-duction) Raman bands are centered at 705 cmminus1 787 cmminus1863 cmminus1 1137 cmminus1 and 1549 cmminus1 An assignation of thepeaks at 705 cmminus1 863 cmminus1 and 1137 cmminus1 is possible withthe indications of Table 2 while the band at 787 cmminus1 and1550 cmminus1 can be assigned to calcium oxidehydroxide andvibration of hydroxyl molecule (O-H out of plane bendingmode) respectively [15 16]
The band at 705 cmminus1 in particular could be assigned toAragonite phase of calcium carbonate The band at 863 cmminus1can be assigned to the ]
2
mode of (CO3
)2minus which is Ramanforbidden in the free ion but remains weak after coupling tothe cations in the lattice [8 34] The broad band at 1137 cmminus1can be assigned to the ]
1
mode due to the symmetricstretching vibration of the carbonate groups [15 16]
The presence in the spectrum of the bands assigned toAragonite and carbonate groupsweakly bonded to the cationsis significant for the happened sequestration of CO
2
by thesamples during the heat treatment
To better understand this phenomenon it is possible toexplain each singular step of the process of carbonationin clays by using experimental archeological methods andreproducing the behavior of the sample
Figure 9(a) shows the Raman spectrum of amorphouscalcium hydroxide Ca(OH)
2
obtained heating calcite pow-ders at the temperature of 1000∘C for 1 h with a ramp oftemperature of 2∘Cmin and after it reached the ambienttemperature mixed with water No other peaks assignableto other stable or metastable crystallographic phases werefound
The bands at 796 cmminus1 913 cmminus1 1187 cmminus1 and1650 cmminus1 are associated to calcium hydroxide and water asindicated by [23 34] In particular the band at 913 cmminus1 couldbe assigned to O-H out of plane bending mode according toBuzgar and Apopei [34]
After 24 h of exposition to the content of CO2
presentin the air at ambient temperature the carbonation process
Journal of Spectroscopy 7
Table 2 (a) Fundamental vibrational modes of the carbonates according to [3 4] (b) Raman bands in some carbonates and hydroxyl-carbonates
Figure 9 Raman spectrum of calcium hydroxide obtained heating at 1000∘C CaCO3
powders
takes place and in the spectrum shown in Figure 9(b) it ispossible to observe the presence of different bands associatedto the carbon dioxide sequestration The band at 913 cmminus1disappears (the band was present in the spectrum taken atthe beginning of the process Figure 9(a)) while it is possibleto observe the presence of the band at 863 cmminus1 which couldbe associated to the mode ]
2
of the carbonate ions weaklybonded to the cations In addition a new band at 740 cmminus1can be observed and assigned to the ]
3
symmetric CO3
2minus
bendingmode inVaterite suggesting favorable conditions forthis metastable form (120583-CaCO
3
) [13]By wetting the same calcium hydroxide powders used in
the previous experiment the ldquolimewashrdquo was realized with thepurpose to reproduce the ancient technique probably used inPompeii The limewash was mixed with hematite and used tocover the surface of two samples of clay indicated as A andB differentiated by the presence of calcite into the mixture(sample A) and no presence of calcite (samples B) into
8 Journal of Spectroscopy
(A) (B)
Figure 10 Laboratory samples sample A calcite in the mixture ofthe clay sample B absence of calcite in the clay Both the sampleswere covered with Fe
Figure 11 Raman spectrumwith deconvolutions of samples (a) and(b)
the mixture (Figure 10) Each sample was treated at 1000∘Cwith the same temperature treatment used in the previouscalcite sample As shown in Figure 10 the samples B present adifferent color in the limewash covered surface
Figure 11 reports the Raman spectra of the samples A andB with the relative deconvolutions with lorentzian profiles Itis possible to observe the presence of the bands assigned tocalcium hydroxide as indicated previously the presence ofthe band around 860 cmminus1 due to CO
3
2minus weakly bonded tothe cations and the presence of the band at 705 cmminus1 typicalfor the ]
4
frequency mode of carbonate in Aragonite phase[9]
Figure 12 reports the Raman spectrum of the sampleA collected in a cross section of the sample not exposedto the atmosphere at high temperature In this case the
Raman shift (cmminus1)
Inte
nsity
(au
)
18002000 1600 1400 1200 1000 800 600 400 200
Correlation factor (R) = 0993
Figure 12 Raman spectrum of the cross section of sample A
calcite present into the clay mixture has been transformedin calcium oxidehydroxide due to the high temperature andthe residual humidity of the clay From the analysis of theRaman spectrum it is possible to observe the phenomenonof carbonation as indicated by the absence of the band at705 cmminus1 (Aragonite phase) and a slow contribution of theband at 860 cmminus1 is shown (associated to the presence ofcarbonate ions weakly bonded to the cations) [9]
These results seems to indicate an high degree of knowl-edge of the cooking process of the pottery in the Romanage and in particular the use of calcium hydroxide as a toolto reduce the content of CO
2
in the furnace atmosphereand then obtain a more oxidant ambient and reach highertemperature close to the at the pottery surfaces
5 Conclusions
In this study a characterization of different type of potterysamples and painted fragments of wall belonging to Pompeiihas been performed by means of EDS microanalysis andRaman spectroscopy The principal results obtained concernthe use of calcium hydroxide above the surface of analyzedsamples before cooking the clay This technique of surfacetreatment seems to be not justified only for the use of avitrification additive or sealant but through this study it ispossible to suggest that calcium hydroxide could be used asldquogetterrdquo of CO
2
during the heat treatment The result of thisoperation is to reduce the content of CO
2
in the furnaceatmosphere and then obtain a more oxidant ambient whencooking the pottery In these conditions as illustrated in thisstudy the metallic oxides used as pigments on the surfaceor contained in the clay mixture could be preserved in thehigher state of oxidation providing a better esthetical result(in terms of color)
In any case these findings give new light on the potterymanufacturing techniques of Romans and in particular opennew questions about the real degree of knowledge of the
Journal of Spectroscopy 9
Romans about the art of ceramics and more general aboutchemistry and technologies
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This study has been supported by the Italian Ministryof University and Scientific Research (MIUR) within thenational grant ldquoFuturo in Ricercardquo 2012 TIME THROUGHCOLOURS Analysis of painted artifacts in their archaeolog-ical historical and sociological contexts (RBFR12405A 002)
References
[1] S P Koob ldquoThe use of Paraloid B-72 as an adhesive itsapplication for archaeological ceramics and other materialsrdquoStudies in Conservation vol 31 no 1 pp 7ndash14 1986
[2] S Chapman and D Mason ldquoLiterature review the use ofParaloid B-72 as a surface consolidant for stained glassrdquo JournalofTheAmerican Institute for Conservation vol 42 no 2 pp 381ndash392 2003
[3] L Burgio and R J H Clark ldquoLibrary of FT-Raman spectraof pigments minerals pigment media and varnishes andsupplement to existing library of Raman spectra of pigmentswith visible excitationrdquo Spectrochimica Acta Part A Molecularand Biomolecular Spectroscopy vol 57 no 7 pp 1491ndash1521 2001
[4] F A Cotton Chemical Applications of Group Theory Wiley-Interscience Richardson Tex USA 3rd edition 1990
[5] S Gunasekaran G Anbalagan and S Pandi ldquoRaman andinfrared spectra of carbonates of calcite structurerdquo Journal ofRaman Spectroscopy vol 37 no 9 pp 892ndash899 2006
[6] N Koura S Kohara K Takeuchi et al ldquoAlkali carbonatesRaman spectroscopy ab initio calculations and structurerdquoJournal of Molecular Structure vol 382 no 3 pp 163ndash169 1996
[7] E Mattei G de Vivo A de Santis C Gaetani C Pelosiand U Santamaria ldquoRaman spectroscopic analysis of azuriteblackeningrdquo Journal of Raman Spectroscopy vol 39 no 2 pp302ndash306 2008
[8] E B Scheetz and B W White ldquoVibrational spectra of thealkaline earth double carbonatesrdquo American Mineralogist vol62 pp 36ndash50 1977
[9] J E Parker S P Thompson A R Lennie J Potter andC C Tang ldquoA study of the aragonite-calcite transformationusingRaman spectroscopy synchrotron powder diffraction andscanning electron microscopyrdquo CrystEngComm vol 12 no 5pp 1590ndash1599 2010
[10] D Krishnamurti ldquoThe Raman spectra of aragonite strontianiteand witheriterdquo Proceedings of the Indian Academy of Sciences Avol 51 no 6 pp 285ndash295 1960
[11] J Urmos S K Sharma and F T Mackenzie ldquoCharacterizationof some biogenic carbonates with Raman spectroscopyrdquo Amer-ican Mineralogist vol 76 no 3-4 pp 641ndash646 1991
[12] M Charles R Jeanloz and R J Hemley ldquoSpectroscopic andx-ray diffraction studies of metastable crystalline-amorphoustransitions in Ca(OH)
2
and serpentinerdquo Geophysical Mono-graph Series vol 67 pp 485ndash492 1992
[13] R W Gauldie S K Sharma and E Volk ldquoMicro-Ramanspectral study of vaterite and aragonite otoliths of the cohosalmon Oncorhynchus kisutchrdquo Comparative Biochemistry andPhysiology A vol 118 no 3 pp 753ndash757 1997
[14] R L Frost W N Martens L Rintoul E Mahmutagic andJ T Kloprogge ldquoRaman spectroscopic study of azurite andmalachite at 298 and 77 Krdquo Journal of Raman Spectroscopy vol33 no 4 pp 252ndash259 2002
[15] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons New York NY USA1997
[16] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons Hoboken NJ USA6th edition 2009
[17] G D Smith and R J H Clark ldquoRaman microscopy inarchaeological sciencerdquo Journal of Archaeological Science vol 31no 8 pp 1137ndash1160 2004
[18] D Bersani and J M Madariaga ldquoApplications of Raman spec-troscopy in art and archaeologyrdquo Journal of Raman Spectroscopyvol 43 no 11 pp 1523ndash1528 2012
[19] L Stagi J A De Toro A Ardu et al ldquoSurface effects undervisible irradiation and heat treatment on the phase stability of120574-Fe2
O3
nanoparticles and 120574-Fe2
O3
-SiO2
core-shell nanostruc-turesrdquo The Journal of Physical Chemistry C vol 118 no 5 pp2857ndash2866 2014
[20] D Hradil T Grygar J Hradilova and P Bezdicka ldquoClay andiron oxide pigments in the history of paintingrdquo Applied ClayScience vol 22 no 5 pp 223ndash236 2003
[21] I Aliatis D Bersani E Campani et al ldquoPigments used inRoman wall paintings in the Vesuvian areardquo Journal of RamanSpectroscopy vol 41 no 11 pp 1537ndash1542 2010
[22] H GM Edwards DW Farwell D L A de Faria et al ldquoRamanspectroscopic study of 3000minusyearminusold human skeletal remainsfrom a sambaqui Santa Catarina Brazilrdquo Journal of RamanSpectroscopy vol 32 no 1 pp 17ndash22 2001
[23] T Y Kwon T Fujishima and Y Imai ldquoFT-Raman spectroscopyof calcium hydroxide medicament in root canalsrdquo InternationalEndodontic Journal vol 37 no 7 pp 489ndash493 2004
[24] R L Frost ldquoFourier transform Raman spectroscopy of kaolin-ite dickite and halloysiterdquo Clays amp Clay Minerals vol 43 no 2pp 191ndash195 1995
[25] I C Freestone ldquoApplications and potential of electron probemicro analysis in technological and provenance investigationsof ancient ceramicsrdquo Archaeometry vol 24 no 2 pp 99ndash1161982
[26] P C Ricci C M Carbonaro L Stagi et al ldquoAnatase-to-rutilephase transition in TiO
2
nanoparticles irradiated by visiblelightrdquo Journal of Physical Chemistry C vol 117 no 15 pp 7850ndash7857 2013
[27] P C Ricci A Casu M Salis R Corpino and A AneddaldquoOptically controlled phase variation of TiO
2
nanoparticlesrdquoJournal of Physical Chemistry C vol 114 no 34 pp 14441ndash144452010
[28] S Sanchez-Moral L Luque J-C Canaveras V Soler J Garcia-Guinea and A Aparicio ldquoLime-pozzolana mortars in Romancatacombs composition structures and restorationrdquo Cementand Concrete Research vol 35 no 8 pp 1555ndash1565 2005
[29] H G M Edwards and D W Farwell ldquoThe conservationalheritage of wall paintings and buildings an FT-Raman spectro-scopic study of prehistoric Roman mediaeval and Renaissance
10 Journal of Spectroscopy
lime substrates and mortarsrdquo Journal of Raman Spectroscopyvol 39 no 8 pp 985ndash992 2008
[30] C M Sinopoli Approaches to Archaeological CeramicsSpringer Boston Mass USA 1991
[31] R Newcomb Jr Ceramic WhitewaresmdashHistory Technology andApplications Pitman Publishing New York NY USA 1947
[32] W J J Huijgen and R N J Comans ldquoCarbon dioxide seques-tration by mineral carbonation literature reviewrdquo ECN ReportECN-C-03-016 ECN 2003
[33] W Gu D W Bousfield and C P Tripp ldquoFormation of calciumcarbonate particles by direct contact of Ca(OH)
[34] N Buzgar and A I Apopei ldquoThe Raman study of certaincarbonatesrdquo Geologie vol 15 pp 97ndash112 2009
[35] S Ekbundit K Leinenweber J L Yarger J S Robinson MVerhelst-Voorhees and G H Wolf ldquoNew high-pressure phaseand pressure-induced amorphization of Ca(OH)
2
grain sizeeffectrdquo Journal of Solid State Chemistry vol 126 no 2 pp 300ndash307 1996
Research ArticleRaman Study on Pompeii Potteries The Role of CalciumHydroxide on the Surface Treatment
Daniele Chiriu1 Pier Carlo Ricci1 Andrea Polcaro2 Paolo Braconi2
David Lanzi2 and Davide Nadali3
1Dipartimento di Fisica Universita di Cagliari sp n 8 Km 0700 Monserrato 09042 Cagliari Italy2Dipartimento di Lettere-Lingue Letterature e Civiltarsquo Antiche E Moderne Universita di Perugia Via Armonica 306123 Perugia Italy3Dipartimento di Scienze dellrsquoAntichita Sapienza Universita di Roma Via dei Volsci 122 00185 Roma Italy
Correspondence should be addressed to Pier Carlo Ricci carloriccidsfunicait
Received 28 October 2014 Accepted 17 December 2014 Published 31 December 2014
Academic Editor Petre Makreski
Copyright copy 2014 Daniele Chiriu et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
Pottery samples from the Pompeii archaeological site were investigated by IR Raman spectroscopy and EDAX measurements Theanalysis of the Raman spectra of the surfaces reveals the presence calcium hydroxide (peak at about 780 cmminus1) while the calciumcarbonate is totally absent The comparative studies on the carbonation effect of the surfaces were performed on laboratory grownsamples of calcium hydroxide The samples were treated at high temperature and exposed to different ambient conditions and theanalysis suggests that the original surfaces of Roman pottery were scattered by calcium hydroxide (limewash) before the cookingprocess in the furnaceThe result of this surface treatment not only permits a vitrification of the surfaces but also seems to reduce thecontent of CO
2
in the furnace atmosphere and then obtain a more oxidant ambient during the cooking of the potteryThese resultsgive new insights on the real degree of knowledge of the Romans about the art of ceramics andmore generally about chemistry andtechnologies
1 Introduction
Nowadays the use of technological experimental techniquesin the field of cultural heritage is widely accepted anddiffused The amount of information that a joint approachbetween physics chemistry and archeology is sensiblyincreased and the efforts in this direction are always growingThe problem that is emerging with the diffusion of tech-nologies is the needed of ldquopurerdquo sample intending the studyof samples that were not altered after their recovery Thistrivial consideration increases its importance when we aredealing with samples that were found decades or centuriesago when the treatment for restoration was not so accurateand they were not deeply studied with particular regard totheir influence on the same samples with time In this senseone example is the use of Paraloid Paraloid is an acrylicresin which used a stabilizing of the samples that intensify thecolors and the brilliance of the surfaces and at the same time
decreases the effect of environmental at the surface Howeverthe use of Paraloid in some sense decreases the possibilitiesto perform further analysis on the treated samples In thissense the use of untreated samples ismandatory to gather newinformation in cultural heritage in particular in well-knownarchaeological excavations [1 2]
This paper displays the results of studies on differentsamples founded during the excavations guided by Peru-giarsquos University among 2004 and 2008 for the ldquoRegio VIrdquoproject (Figure 1) in the framework of the project ldquotimethrough colorsrdquo funded by the Italian Ministry of Universityand Scientific Research within the national grant ldquoFuturoin Ricercardquo 2012 Studies on productionrsquos scraps come toknow some technical details related to the so-called ldquoPro-ductionrsquos Archaeologyrdquo These technical details specificallyconcern the heat treatmentrsquos temperature of ceramic waresthe composition of clay the type of coating and the typeof ambient generated during the heat treatment (oxidative
Hindawi Publishing CorporationJournal of SpectroscopyVolume 2014 Article ID 435026 10 pageshttpdxdoiorg1011552014435026
2 Journal of Spectroscopy
Figure 1 Comprehensive view of the archaeological site of Pompeii(Region VI)
Figure 2 Furnace situated below the triclinium of domus VII 159-10
or reductive) Part of the samples consists of productionrsquosscraps of two manufacturing centres now located below thefoundations of domusVI 5 9ndash19 and domusVII 15 9-10Theother part consists instead of plasters founded in differentstratigraphical units of domus VII 15 1-2 also known asldquoCasa del Marinaiordquo
During the 2004 excavations a furnace was found amongthe foundations of domus VI 5 9ndash19 (furnace VI) This fur-nace was built with a twin praefurnium and a quadrangularcombustion roomThis manufacturing centre dates back to aperiod between the end of the IIIrd century bC and the halfof the IInd century bC as evidenced by productionrsquos scrapsThe production consists mainly of dolia large containerssome kinds of ldquoollardquo in common ware and pans in internalred slip ware
The furnace situated below the triclinium of domus VII15 9-10 (furnace VII) produced instead amphora cookingware common ware and internal red slip ware (cumanaetestae) All the samples can be dated at the beginning of theIInd century bC (Figure 2)
Studies on plasters take moves to verify the chemical andphysical transformations caused by the thermal shock due toVesuviursquos eruption of 79 AD Plasters were founded in 2007on a trench inside the second atrium (amb I) of the so-calledldquoCasa del Marinaiordquo
In this paper we report the Raman spectra the vibra-tional analysis and the EDAX measurements on the abovementioned archeological samples and for comparison withsamples grown and treated specifically in laboratory
Being applied in archaeology only in the recent yearsRaman spectroscopy is becoming increasingly important
as an analytical tool in conservation science [17 18] Itsrelevance is given by the intrinsic properties of the techniqueactually Raman spectra are obtained by excitation with lowenergy radiation by contrast with common ldquoarchaeologyrdquoexperimental techniques such as Mossbauer spectroscopyand Electronic Spin Resonance Raman spectroscopy is com-pletely not destructive and does not need any pretreatmentof the samples Moreover thanks to the advances in thetechnology devices in the recent years it is possible to collectexcellent experimental data in situ by means of opticalfiber coupled devices with small and compact dispersiveapparatusThepossibilities to utilize an excitationwavelengthat 1064 nm and collect an efficient Raman signal are of partic-ular relevance in untreated samples where the luminescencesignal often overlaps and masks the weak Raman signals
A deep scientific study by means of nondestructive andtechnologically advanced techniques on untreated potterysamples from the archeological excavation of Pompeii cangive new light on the pottery manufacturing methods ofRomans and more in general about the art of ceramics inRomanrsquos age
2 Materials and Methods
Raman scattering measurements were carried out in backscattering geometry with the 1064 nm line of an NdYAGlaser Measurements were performed in air at room tem-perature with a compact spectrometer BWTEK i-RamanEx integrated system with a spectral resolution of about9 cmminus1 Chemical analysis was carried out by using EDAXmicroanalysis system of a Dual Beam FEI Nova
Different samples originating to mention two furnaces(furnace VI and Furnace VII) in Pompeii were analyzed Forsake of clarity and brevity we choose as representative ofthe different samples the fragments denoted by VII59B11 andVI59B7Z for the furnaces VII and VI respectively (Figures3(a) and 3(b)) However if it is not explicitly indicated nodifferences in the measurements performed were observedwith respect to other samples with the same provenienceor inside the same sample itself Moreover the sample659A14730 (Figure 3(c)) a clear waste of production wasused as comparative sample
Raman analysis interested also two different plasterrsquossamples
(i) the first sample (sample HT) was a IVth style paintingexposed to the heat of the eruption This sample wasoriginally situated on the US 1 at 35003 meters asl
(ii) the second sample (sample LT) was instead a Ist stylepainting dated to the IIIrd century bC and notexposed to the heat of the eruption This sample wasin fact situated on the US 22 at 33803ndash33863 metersasl and was covered by 14 meters of ground duringthe eruption
3 Experimental Results
The internal and external faces of the VI 59B7Z samplewere analyzed byRaman spectroscopy EDAXmeasurements
Journal of Spectroscopy 3
(a) (b) (c)
Figure 3 Images of the samples VII59B11 (a) VI59B7Z (b) and 659A14730 (c)
450 300
1200 1000 800 600 400
ExternalInternal
VI59B7Z
Inte
nsity
(au
)
Raman shift (cmminus1)
(a)
450600
1200 1000 800 600 400
ExternalInternal
Inte
nsity
(au
)
A A AR R
Raman shift (cmminus1)
(b)
Figure 4 Raman spectra of the external and internal surface of samples VI59B7Z (a) and VII59B11The inset in the (a) section is an enlargedview of the external surfaces of sample VI59B7Z The inset in the (b) section reports the Raman spectrum form the cross section of sampleVII59B11 The peaks are identified as TiO
2
in the anatase (indicated with A) and rutile phase (R)
and SEM images the Raman Figure 4(a) reports the Ramanspectra a large band between 600 and 900 cmminus1 centered atabout 780 cmminus1 is present in both the spectra and no otherpeaks are easily distinguishable in the spectrum relative tointernal surface On the contrary the Raman spectrum ofthe red external surface of the sample VI 59B7Z present alsopeaks at 226 292 and 411 cmminus1 assignable to the hematitephase of the iron oxide (inset Figure 4(a)) [19] Actually theuse of iron oxides in different polymorph as red pigmentsis widely stated [18 20 21] The Romans achieved differentcolours from deep red to purple through the grinding ofhematite crystals The particle size affects the colour wherevery fine particles on a nanometer scale gave purple
According to [22 23] the large peaks at 780 cmminus1 can beassigned to the presence of calcium oxide and calcium hydrox-ideAs a confirmation the EDAXanalysis (Figure 5)was takenalong the different surfaces the peaks of calcium and Ironare well evident several elements have also been detected inthe samples probably arising from natural minerals presentin the proximity of the excavation site such as quartz (SiO
2
)feldspars leucite (KAlSi
2
O6
) and kaolinite (Al2
Si2
O5
(OH)4
)[24 25]
To better observe differences between the clay and thesurface of the pottery the samples were analyzed also inthe cracks of the surfaces and in cross section the Ramanspectrum does not reveal any presence of calcium hydroxideand the EDAX analysis reveals a small and reduced presenceof calcium while the relative presence of different elementsremains almost unaltered (Table 1)
In the sample VII59B11 (furnace VII) the Raman spectrataken along the cross section randomly present peaks at395 450 517 and 635 cmminus1 (see inset in Figure 4(b)) Threeof them are easily assignable to the presence of TiO
2
inthe anatase phase while the peak at 450 cmminus1 and theenlargement of the band at 635 cmminus1 suggest the presenceof TiO
2
in the rutile phase [26 27] It is worth noting thatthese elements are present only as tracewith respect to jumbleand the relative high intensity of the Raman signal is dueto the high efficiency of these materials and phases [26 27]In most of the other samples these peaks were not observedsuggesting the random presence of titanium oxide in thestarting material Again the Raman signal arising from thesurfaces is dominated by the large by assigned to the presenceof calcium oxidehydroxide (Figure 4(b))
4 Journal of Spectroscopy
Table 1
(a)
Element Wt At 119870-ratio 119885 119860 119865
C K 1599 2876 00481 10720 02805 10005O K 3812 5146 00780 10531 01943 10003Mg K 123 109 00053 10085 04310 10012Al K 160 128 00088 09784 05614 10019Si K 304 234 00208 10079 06754 10019K K 037 020 00032 09572 08983 10257Ca K 1809 975 01643 09789 09245 10034Fe K 1015 392 00886 08913 09776 10024Pb L 1141 119 00719 09181 10189 10000Total 10000 10000
(b)
Element Wt At 119870-ratio 119885 119860 119865
C K 1526 2515 00331 10540 02058 10004O K 4131 5110 01138 10355 02661 10003Mg K 150 122 00082 09920 05523 10044Al K 683 501 00448 09625 06778 10055Si K 1460 1029 01061 09900 07328 10011K K 209 106 00183 09395 09214 10117Ca K 705 348 00638 09608 09391 10027Fe K 619 219 00537 08717 09939 10017Pb L 516 049 00315 05993 10185 10000Total 10000 10000
C
Ca
Si
MgFe
Fe
K
AlPb
O
200 400 600 800
(a)
C
Ca
Si
MgFe Fe
K
Al
Pb
O
200 400 600 800
(b)
Figure 5 EDAX spectra from VI59B7Z sample taken on the surface (a) and cross section (b)
Journal of Spectroscopy 5
4 Discussion
The presence of the calcium oxide and hydroxide on theinternal and external surfaces of the samples as well as thecontemporary absence in the analysis of the cross sectionsand in the cracks strongly suggests that the calciumhydroxidewas not accidental on the surface but on the contrary it wasspread intentionally over both the surfaces of the potteries
On the other hand the use of limewash as binder of differ-ent pigments is widely proved and accepted in antiquities andin particular in ancient Roman walls [21 28 29] Accordingto Vitruvius intonaco is a set of finishing layers composedof lime and very fine-grained sand In this technique thecalcareous rock (mainly constituted by calcium carbonate(CaCO
3
)) is first selected in base to their purity (smallimpurity can vary the final color of the powder) then washeated in oven at high temperature (more than 1000∘C) Inthese conditions the calcium carbonate degrades in calciumoxide and carbon dioxide [21]
CaCO3(S) + heat 997888rarr CaO
(S) + CO2(G) (1)
Then the calcium oxide was mixed with water formingcalcium hydroxide
CaO3(S) +H2O 997888rarr Ca (OH)
2
(2)
Finally this compound (calcium oxidehydroxide) wasmixed again with calcium carbonate to obtain the so-calledintonaco that was applied to the wall in order to obtaina smooth polished surface that resembles marble To thiscompound often mineral pigments were added to formdifferent color on the wall Different works based on Ramanspectroscopy reveal the ill resolved double at 710ndash790 cmminus1due to the calcium oxidehydroxide plus a narrow band at1085 cmminus1 from the calcium carbonate
Some general and additional information can be deducedfrom the study of the Raman spectra of the intonaco actuallythe presence of the band from calcium carbonate is a clearindication that the samples were treated at high temperatureactually as previously stated at high temperature (above550∘C) calcium carbonate passes in calcium oxide (plusgaseous CO
2
) that being highly hygroscopic forms naturallythe calcium oxidehydroxide (CaO(OH)) In general whenthe samples were treated at relative low temperature boththe Raman signals from calcium carbonate and calciumoxidehydroxide are present as in the case of Roman muralpaints being the mural paint not thermal treated On thecontrary in our samples the absence of the band of carbonateas reported in Figures 4(a) and 4(b) can be used as anindication of a thermal treatment of the pottery samples athigh temperature
An interesting proof of the above mentioned heat effectis evident in the Raman spectra of the mural samples (casadel marinaio) Both of them refer to mural paintings fromPompeii but only the first of them (sampleHT)was in contactwith the high temperature generated by Vesuviusrsquos eruptionand the Raman signal from this sample does not presentthe peak at 1085 cmminus1 while the second sample (sample LT)pertains to a wall that was about three meters under the
Raman shift (cmminus1)
Inte
nsity
(au
)
1086 cmminus1
1200 1150 1100 1050 1000
Not exposed to eruptionExposed to eruption
Figure 6 Raman spectra taken on mural samples from casadel marinaio (Pompeii) exposed and not exposed to Vesuviusrsquoseruption The band position relative to the strongest Raman bandfrom the calcium carbonate is evidenced
ground level at the time of the eruption so the temperaturewas much lower and the calcium carbonate over the muralpainting was preserved (Figure 6)
On the contrary in the pottery samples from Pompeii(see the spectra from the VII59B11 VI 59B7Z samples asrepresentative in Figure 4) the band at 1085 cmminus1 is alwaysabsent in all the measurements performed suggesting thatthe limewash was spread over the pottery before the heattreatment in the furnace As further indication of this hypoth-esiswe report theRaman spectrumof the sample 659 A14730a clear waste of production (Figure 7) Again the band at780 cmminus1 is evident while the band of calcium carbonate isabsentThe spectrum of the jumble registered in cross sectiondoes not reveal any peak of this phase suggesting again thatthe limewash (calcium oxidehydroxide) was spread over thesurface before the heating treatment
It can be interesting to try to answer the question whichis the function of the calcium oxidehydroxide and why itwas spread over the surface of the pottery before the heattreatment
One hypothesis can be related to the same reason of themural painting that is to smooth the surfaces and to use theintonaco as a binder of the inorganic pigment (that need athermal treatment)
A secondhypothesis can be associated to an improvementto the normal cooking process of the pottery Actually theaddition of calcium oxidehydroxide creates a layer overthe surfaces that during the heat treatment remains highlyoxygenatedThe oxygen preserves the surfaces from carbona-ceous waste that blacken the final good moreover the oxygenpermits to obtain a relative higher temperature at the surfacesfavoring the vitrification process of the aluminosilicates
6 Journal of Spectroscopy
Raman shift (cmminus1)
1400 1200 1000 800 600 400
Cross sectionExternal
659 A14730
Inte
nsity
(au
)
Figure 7 Raman spectrumof the sample 659A14730 a clearwaste ofproduction of the furnace VII taken along the internal and externalsurfaces
the hardening of the clay and decreasing the porosity of thesurfaces [30 31]
The high oxygenated ambient of these samples is indi-rectly suggested from the presence of TiO
2
in the anataseforms Actually at temperature higher than 600∘C theanatase phase naturally transforms to the more stable rutilephase however highly oxygenated environmental conditionsincrease the temperature threshold for the phase transforma-tion up to 1000∘C [26]
As experimental proof of the thesis just illustrated withthe help of deconvolutions with lorentzian profiles it ispossible to analyze the Raman spectra in order to identify adegree of carbonation of the samples and then deep inside tothe absorption process of CO
2
during the heat treatment ofthe pottery and justify the use of calcium hydroxide as getterof the carbon dioxide produced during the heat treatmentAs indicated in [32 33] the method of the carbonic dioxidesequestration (CDS) is well kwon and used especially inthe case of the mineral carbonation of calcined calciumhydroxide (limewash) as indicated in the reaction
Ca (OH)2(S) + CO2 997888rarr CaCO
3(S) +H2O (3)
In the case of heat treated pottery thementioned reactiontakes place during the cooling process when the formationof calcium carbonate is allowed Calcium carbonate canassume different crystalline phases as indicated by [11 34]The principal structures are indicated in Table 2 with Ramanband and assignations
Moreover if the time of cooling is too fast it is possible tofind a mixture of mentioned phases with an high probabilityto obtain the compound in amorphous conditions [12 33 35]
The deconvolution illustrates the effective position ofthe experimental Raman bands in the spectra collectedon the ancient potteries (Figure 8 reports as example
the deconvolution from the sample 659 A14730 waste of pro-duction) Raman bands are centered at 705 cmminus1 787 cmminus1863 cmminus1 1137 cmminus1 and 1549 cmminus1 An assignation of thepeaks at 705 cmminus1 863 cmminus1 and 1137 cmminus1 is possible withthe indications of Table 2 while the band at 787 cmminus1 and1550 cmminus1 can be assigned to calcium oxidehydroxide andvibration of hydroxyl molecule (O-H out of plane bendingmode) respectively [15 16]
The band at 705 cmminus1 in particular could be assigned toAragonite phase of calcium carbonate The band at 863 cmminus1can be assigned to the ]
2
mode of (CO3
)2minus which is Ramanforbidden in the free ion but remains weak after coupling tothe cations in the lattice [8 34] The broad band at 1137 cmminus1can be assigned to the ]
1
mode due to the symmetricstretching vibration of the carbonate groups [15 16]
The presence in the spectrum of the bands assigned toAragonite and carbonate groupsweakly bonded to the cationsis significant for the happened sequestration of CO
2
by thesamples during the heat treatment
To better understand this phenomenon it is possible toexplain each singular step of the process of carbonationin clays by using experimental archeological methods andreproducing the behavior of the sample
Figure 9(a) shows the Raman spectrum of amorphouscalcium hydroxide Ca(OH)
2
obtained heating calcite pow-ders at the temperature of 1000∘C for 1 h with a ramp oftemperature of 2∘Cmin and after it reached the ambienttemperature mixed with water No other peaks assignableto other stable or metastable crystallographic phases werefound
The bands at 796 cmminus1 913 cmminus1 1187 cmminus1 and1650 cmminus1 are associated to calcium hydroxide and water asindicated by [23 34] In particular the band at 913 cmminus1 couldbe assigned to O-H out of plane bending mode according toBuzgar and Apopei [34]
After 24 h of exposition to the content of CO2
presentin the air at ambient temperature the carbonation process
Journal of Spectroscopy 7
Table 2 (a) Fundamental vibrational modes of the carbonates according to [3 4] (b) Raman bands in some carbonates and hydroxyl-carbonates
Figure 9 Raman spectrum of calcium hydroxide obtained heating at 1000∘C CaCO3
powders
takes place and in the spectrum shown in Figure 9(b) it ispossible to observe the presence of different bands associatedto the carbon dioxide sequestration The band at 913 cmminus1disappears (the band was present in the spectrum taken atthe beginning of the process Figure 9(a)) while it is possibleto observe the presence of the band at 863 cmminus1 which couldbe associated to the mode ]
2
of the carbonate ions weaklybonded to the cations In addition a new band at 740 cmminus1can be observed and assigned to the ]
3
symmetric CO3
2minus
bendingmode inVaterite suggesting favorable conditions forthis metastable form (120583-CaCO
3
) [13]By wetting the same calcium hydroxide powders used in
the previous experiment the ldquolimewashrdquo was realized with thepurpose to reproduce the ancient technique probably used inPompeii The limewash was mixed with hematite and used tocover the surface of two samples of clay indicated as A andB differentiated by the presence of calcite into the mixture(sample A) and no presence of calcite (samples B) into
8 Journal of Spectroscopy
(A) (B)
Figure 10 Laboratory samples sample A calcite in the mixture ofthe clay sample B absence of calcite in the clay Both the sampleswere covered with Fe
Figure 11 Raman spectrumwith deconvolutions of samples (a) and(b)
the mixture (Figure 10) Each sample was treated at 1000∘Cwith the same temperature treatment used in the previouscalcite sample As shown in Figure 10 the samples B present adifferent color in the limewash covered surface
Figure 11 reports the Raman spectra of the samples A andB with the relative deconvolutions with lorentzian profiles Itis possible to observe the presence of the bands assigned tocalcium hydroxide as indicated previously the presence ofthe band around 860 cmminus1 due to CO
3
2minus weakly bonded tothe cations and the presence of the band at 705 cmminus1 typicalfor the ]
4
frequency mode of carbonate in Aragonite phase[9]
Figure 12 reports the Raman spectrum of the sampleA collected in a cross section of the sample not exposedto the atmosphere at high temperature In this case the
Raman shift (cmminus1)
Inte
nsity
(au
)
18002000 1600 1400 1200 1000 800 600 400 200
Correlation factor (R) = 0993
Figure 12 Raman spectrum of the cross section of sample A
calcite present into the clay mixture has been transformedin calcium oxidehydroxide due to the high temperature andthe residual humidity of the clay From the analysis of theRaman spectrum it is possible to observe the phenomenonof carbonation as indicated by the absence of the band at705 cmminus1 (Aragonite phase) and a slow contribution of theband at 860 cmminus1 is shown (associated to the presence ofcarbonate ions weakly bonded to the cations) [9]
These results seems to indicate an high degree of knowl-edge of the cooking process of the pottery in the Romanage and in particular the use of calcium hydroxide as a toolto reduce the content of CO
2
in the furnace atmosphereand then obtain a more oxidant ambient and reach highertemperature close to the at the pottery surfaces
5 Conclusions
In this study a characterization of different type of potterysamples and painted fragments of wall belonging to Pompeiihas been performed by means of EDS microanalysis andRaman spectroscopy The principal results obtained concernthe use of calcium hydroxide above the surface of analyzedsamples before cooking the clay This technique of surfacetreatment seems to be not justified only for the use of avitrification additive or sealant but through this study it ispossible to suggest that calcium hydroxide could be used asldquogetterrdquo of CO
2
during the heat treatment The result of thisoperation is to reduce the content of CO
2
in the furnaceatmosphere and then obtain a more oxidant ambient whencooking the pottery In these conditions as illustrated in thisstudy the metallic oxides used as pigments on the surfaceor contained in the clay mixture could be preserved in thehigher state of oxidation providing a better esthetical result(in terms of color)
In any case these findings give new light on the potterymanufacturing techniques of Romans and in particular opennew questions about the real degree of knowledge of the
Journal of Spectroscopy 9
Romans about the art of ceramics and more general aboutchemistry and technologies
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This study has been supported by the Italian Ministryof University and Scientific Research (MIUR) within thenational grant ldquoFuturo in Ricercardquo 2012 TIME THROUGHCOLOURS Analysis of painted artifacts in their archaeolog-ical historical and sociological contexts (RBFR12405A 002)
References
[1] S P Koob ldquoThe use of Paraloid B-72 as an adhesive itsapplication for archaeological ceramics and other materialsrdquoStudies in Conservation vol 31 no 1 pp 7ndash14 1986
[2] S Chapman and D Mason ldquoLiterature review the use ofParaloid B-72 as a surface consolidant for stained glassrdquo JournalofTheAmerican Institute for Conservation vol 42 no 2 pp 381ndash392 2003
[3] L Burgio and R J H Clark ldquoLibrary of FT-Raman spectraof pigments minerals pigment media and varnishes andsupplement to existing library of Raman spectra of pigmentswith visible excitationrdquo Spectrochimica Acta Part A Molecularand Biomolecular Spectroscopy vol 57 no 7 pp 1491ndash1521 2001
[4] F A Cotton Chemical Applications of Group Theory Wiley-Interscience Richardson Tex USA 3rd edition 1990
[5] S Gunasekaran G Anbalagan and S Pandi ldquoRaman andinfrared spectra of carbonates of calcite structurerdquo Journal ofRaman Spectroscopy vol 37 no 9 pp 892ndash899 2006
[6] N Koura S Kohara K Takeuchi et al ldquoAlkali carbonatesRaman spectroscopy ab initio calculations and structurerdquoJournal of Molecular Structure vol 382 no 3 pp 163ndash169 1996
[7] E Mattei G de Vivo A de Santis C Gaetani C Pelosiand U Santamaria ldquoRaman spectroscopic analysis of azuriteblackeningrdquo Journal of Raman Spectroscopy vol 39 no 2 pp302ndash306 2008
[8] E B Scheetz and B W White ldquoVibrational spectra of thealkaline earth double carbonatesrdquo American Mineralogist vol62 pp 36ndash50 1977
[9] J E Parker S P Thompson A R Lennie J Potter andC C Tang ldquoA study of the aragonite-calcite transformationusingRaman spectroscopy synchrotron powder diffraction andscanning electron microscopyrdquo CrystEngComm vol 12 no 5pp 1590ndash1599 2010
[10] D Krishnamurti ldquoThe Raman spectra of aragonite strontianiteand witheriterdquo Proceedings of the Indian Academy of Sciences Avol 51 no 6 pp 285ndash295 1960
[11] J Urmos S K Sharma and F T Mackenzie ldquoCharacterizationof some biogenic carbonates with Raman spectroscopyrdquo Amer-ican Mineralogist vol 76 no 3-4 pp 641ndash646 1991
[12] M Charles R Jeanloz and R J Hemley ldquoSpectroscopic andx-ray diffraction studies of metastable crystalline-amorphoustransitions in Ca(OH)
2
and serpentinerdquo Geophysical Mono-graph Series vol 67 pp 485ndash492 1992
[13] R W Gauldie S K Sharma and E Volk ldquoMicro-Ramanspectral study of vaterite and aragonite otoliths of the cohosalmon Oncorhynchus kisutchrdquo Comparative Biochemistry andPhysiology A vol 118 no 3 pp 753ndash757 1997
[14] R L Frost W N Martens L Rintoul E Mahmutagic andJ T Kloprogge ldquoRaman spectroscopic study of azurite andmalachite at 298 and 77 Krdquo Journal of Raman Spectroscopy vol33 no 4 pp 252ndash259 2002
[15] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons New York NY USA1997
[16] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons Hoboken NJ USA6th edition 2009
[17] G D Smith and R J H Clark ldquoRaman microscopy inarchaeological sciencerdquo Journal of Archaeological Science vol 31no 8 pp 1137ndash1160 2004
[18] D Bersani and J M Madariaga ldquoApplications of Raman spec-troscopy in art and archaeologyrdquo Journal of Raman Spectroscopyvol 43 no 11 pp 1523ndash1528 2012
[19] L Stagi J A De Toro A Ardu et al ldquoSurface effects undervisible irradiation and heat treatment on the phase stability of120574-Fe2
O3
nanoparticles and 120574-Fe2
O3
-SiO2
core-shell nanostruc-turesrdquo The Journal of Physical Chemistry C vol 118 no 5 pp2857ndash2866 2014
[20] D Hradil T Grygar J Hradilova and P Bezdicka ldquoClay andiron oxide pigments in the history of paintingrdquo Applied ClayScience vol 22 no 5 pp 223ndash236 2003
[21] I Aliatis D Bersani E Campani et al ldquoPigments used inRoman wall paintings in the Vesuvian areardquo Journal of RamanSpectroscopy vol 41 no 11 pp 1537ndash1542 2010
[22] H GM Edwards DW Farwell D L A de Faria et al ldquoRamanspectroscopic study of 3000minusyearminusold human skeletal remainsfrom a sambaqui Santa Catarina Brazilrdquo Journal of RamanSpectroscopy vol 32 no 1 pp 17ndash22 2001
[23] T Y Kwon T Fujishima and Y Imai ldquoFT-Raman spectroscopyof calcium hydroxide medicament in root canalsrdquo InternationalEndodontic Journal vol 37 no 7 pp 489ndash493 2004
[24] R L Frost ldquoFourier transform Raman spectroscopy of kaolin-ite dickite and halloysiterdquo Clays amp Clay Minerals vol 43 no 2pp 191ndash195 1995
[25] I C Freestone ldquoApplications and potential of electron probemicro analysis in technological and provenance investigationsof ancient ceramicsrdquo Archaeometry vol 24 no 2 pp 99ndash1161982
[26] P C Ricci C M Carbonaro L Stagi et al ldquoAnatase-to-rutilephase transition in TiO
2
nanoparticles irradiated by visiblelightrdquo Journal of Physical Chemistry C vol 117 no 15 pp 7850ndash7857 2013
[27] P C Ricci A Casu M Salis R Corpino and A AneddaldquoOptically controlled phase variation of TiO
2
nanoparticlesrdquoJournal of Physical Chemistry C vol 114 no 34 pp 14441ndash144452010
[28] S Sanchez-Moral L Luque J-C Canaveras V Soler J Garcia-Guinea and A Aparicio ldquoLime-pozzolana mortars in Romancatacombs composition structures and restorationrdquo Cementand Concrete Research vol 35 no 8 pp 1555ndash1565 2005
[29] H G M Edwards and D W Farwell ldquoThe conservationalheritage of wall paintings and buildings an FT-Raman spectro-scopic study of prehistoric Roman mediaeval and Renaissance
10 Journal of Spectroscopy
lime substrates and mortarsrdquo Journal of Raman Spectroscopyvol 39 no 8 pp 985ndash992 2008
[30] C M Sinopoli Approaches to Archaeological CeramicsSpringer Boston Mass USA 1991
[31] R Newcomb Jr Ceramic WhitewaresmdashHistory Technology andApplications Pitman Publishing New York NY USA 1947
[32] W J J Huijgen and R N J Comans ldquoCarbon dioxide seques-tration by mineral carbonation literature reviewrdquo ECN ReportECN-C-03-016 ECN 2003
[33] W Gu D W Bousfield and C P Tripp ldquoFormation of calciumcarbonate particles by direct contact of Ca(OH)
[34] N Buzgar and A I Apopei ldquoThe Raman study of certaincarbonatesrdquo Geologie vol 15 pp 97ndash112 2009
[35] S Ekbundit K Leinenweber J L Yarger J S Robinson MVerhelst-Voorhees and G H Wolf ldquoNew high-pressure phaseand pressure-induced amorphization of Ca(OH)
2
grain sizeeffectrdquo Journal of Solid State Chemistry vol 126 no 2 pp 300ndash307 1996
Figure 1 Comprehensive view of the archaeological site of Pompeii(Region VI)
Figure 2 Furnace situated below the triclinium of domus VII 159-10
or reductive) Part of the samples consists of productionrsquosscraps of two manufacturing centres now located below thefoundations of domusVI 5 9ndash19 and domusVII 15 9-10Theother part consists instead of plasters founded in differentstratigraphical units of domus VII 15 1-2 also known asldquoCasa del Marinaiordquo
During the 2004 excavations a furnace was found amongthe foundations of domus VI 5 9ndash19 (furnace VI) This fur-nace was built with a twin praefurnium and a quadrangularcombustion roomThis manufacturing centre dates back to aperiod between the end of the IIIrd century bC and the halfof the IInd century bC as evidenced by productionrsquos scrapsThe production consists mainly of dolia large containerssome kinds of ldquoollardquo in common ware and pans in internalred slip ware
The furnace situated below the triclinium of domus VII15 9-10 (furnace VII) produced instead amphora cookingware common ware and internal red slip ware (cumanaetestae) All the samples can be dated at the beginning of theIInd century bC (Figure 2)
Studies on plasters take moves to verify the chemical andphysical transformations caused by the thermal shock due toVesuviursquos eruption of 79 AD Plasters were founded in 2007on a trench inside the second atrium (amb I) of the so-calledldquoCasa del Marinaiordquo
In this paper we report the Raman spectra the vibra-tional analysis and the EDAX measurements on the abovementioned archeological samples and for comparison withsamples grown and treated specifically in laboratory
Being applied in archaeology only in the recent yearsRaman spectroscopy is becoming increasingly important
as an analytical tool in conservation science [17 18] Itsrelevance is given by the intrinsic properties of the techniqueactually Raman spectra are obtained by excitation with lowenergy radiation by contrast with common ldquoarchaeologyrdquoexperimental techniques such as Mossbauer spectroscopyand Electronic Spin Resonance Raman spectroscopy is com-pletely not destructive and does not need any pretreatmentof the samples Moreover thanks to the advances in thetechnology devices in the recent years it is possible to collectexcellent experimental data in situ by means of opticalfiber coupled devices with small and compact dispersiveapparatusThepossibilities to utilize an excitationwavelengthat 1064 nm and collect an efficient Raman signal are of partic-ular relevance in untreated samples where the luminescencesignal often overlaps and masks the weak Raman signals
A deep scientific study by means of nondestructive andtechnologically advanced techniques on untreated potterysamples from the archeological excavation of Pompeii cangive new light on the pottery manufacturing methods ofRomans and more in general about the art of ceramics inRomanrsquos age
2 Materials and Methods
Raman scattering measurements were carried out in backscattering geometry with the 1064 nm line of an NdYAGlaser Measurements were performed in air at room tem-perature with a compact spectrometer BWTEK i-RamanEx integrated system with a spectral resolution of about9 cmminus1 Chemical analysis was carried out by using EDAXmicroanalysis system of a Dual Beam FEI Nova
Different samples originating to mention two furnaces(furnace VI and Furnace VII) in Pompeii were analyzed Forsake of clarity and brevity we choose as representative ofthe different samples the fragments denoted by VII59B11 andVI59B7Z for the furnaces VII and VI respectively (Figures3(a) and 3(b)) However if it is not explicitly indicated nodifferences in the measurements performed were observedwith respect to other samples with the same provenienceor inside the same sample itself Moreover the sample659A14730 (Figure 3(c)) a clear waste of production wasused as comparative sample
Raman analysis interested also two different plasterrsquossamples
(i) the first sample (sample HT) was a IVth style paintingexposed to the heat of the eruption This sample wasoriginally situated on the US 1 at 35003 meters asl
(ii) the second sample (sample LT) was instead a Ist stylepainting dated to the IIIrd century bC and notexposed to the heat of the eruption This sample wasin fact situated on the US 22 at 33803ndash33863 metersasl and was covered by 14 meters of ground duringthe eruption
3 Experimental Results
The internal and external faces of the VI 59B7Z samplewere analyzed byRaman spectroscopy EDAXmeasurements
Journal of Spectroscopy 3
(a) (b) (c)
Figure 3 Images of the samples VII59B11 (a) VI59B7Z (b) and 659A14730 (c)
450 300
1200 1000 800 600 400
ExternalInternal
VI59B7Z
Inte
nsity
(au
)
Raman shift (cmminus1)
(a)
450600
1200 1000 800 600 400
ExternalInternal
Inte
nsity
(au
)
A A AR R
Raman shift (cmminus1)
(b)
Figure 4 Raman spectra of the external and internal surface of samples VI59B7Z (a) and VII59B11The inset in the (a) section is an enlargedview of the external surfaces of sample VI59B7Z The inset in the (b) section reports the Raman spectrum form the cross section of sampleVII59B11 The peaks are identified as TiO
2
in the anatase (indicated with A) and rutile phase (R)
and SEM images the Raman Figure 4(a) reports the Ramanspectra a large band between 600 and 900 cmminus1 centered atabout 780 cmminus1 is present in both the spectra and no otherpeaks are easily distinguishable in the spectrum relative tointernal surface On the contrary the Raman spectrum ofthe red external surface of the sample VI 59B7Z present alsopeaks at 226 292 and 411 cmminus1 assignable to the hematitephase of the iron oxide (inset Figure 4(a)) [19] Actually theuse of iron oxides in different polymorph as red pigmentsis widely stated [18 20 21] The Romans achieved differentcolours from deep red to purple through the grinding ofhematite crystals The particle size affects the colour wherevery fine particles on a nanometer scale gave purple
According to [22 23] the large peaks at 780 cmminus1 can beassigned to the presence of calcium oxide and calcium hydrox-ideAs a confirmation the EDAXanalysis (Figure 5)was takenalong the different surfaces the peaks of calcium and Ironare well evident several elements have also been detected inthe samples probably arising from natural minerals presentin the proximity of the excavation site such as quartz (SiO
2
)feldspars leucite (KAlSi
2
O6
) and kaolinite (Al2
Si2
O5
(OH)4
)[24 25]
To better observe differences between the clay and thesurface of the pottery the samples were analyzed also inthe cracks of the surfaces and in cross section the Ramanspectrum does not reveal any presence of calcium hydroxideand the EDAX analysis reveals a small and reduced presenceof calcium while the relative presence of different elementsremains almost unaltered (Table 1)
In the sample VII59B11 (furnace VII) the Raman spectrataken along the cross section randomly present peaks at395 450 517 and 635 cmminus1 (see inset in Figure 4(b)) Threeof them are easily assignable to the presence of TiO
2
inthe anatase phase while the peak at 450 cmminus1 and theenlargement of the band at 635 cmminus1 suggest the presenceof TiO
2
in the rutile phase [26 27] It is worth noting thatthese elements are present only as tracewith respect to jumbleand the relative high intensity of the Raman signal is dueto the high efficiency of these materials and phases [26 27]In most of the other samples these peaks were not observedsuggesting the random presence of titanium oxide in thestarting material Again the Raman signal arising from thesurfaces is dominated by the large by assigned to the presenceof calcium oxidehydroxide (Figure 4(b))
4 Journal of Spectroscopy
Table 1
(a)
Element Wt At 119870-ratio 119885 119860 119865
C K 1599 2876 00481 10720 02805 10005O K 3812 5146 00780 10531 01943 10003Mg K 123 109 00053 10085 04310 10012Al K 160 128 00088 09784 05614 10019Si K 304 234 00208 10079 06754 10019K K 037 020 00032 09572 08983 10257Ca K 1809 975 01643 09789 09245 10034Fe K 1015 392 00886 08913 09776 10024Pb L 1141 119 00719 09181 10189 10000Total 10000 10000
(b)
Element Wt At 119870-ratio 119885 119860 119865
C K 1526 2515 00331 10540 02058 10004O K 4131 5110 01138 10355 02661 10003Mg K 150 122 00082 09920 05523 10044Al K 683 501 00448 09625 06778 10055Si K 1460 1029 01061 09900 07328 10011K K 209 106 00183 09395 09214 10117Ca K 705 348 00638 09608 09391 10027Fe K 619 219 00537 08717 09939 10017Pb L 516 049 00315 05993 10185 10000Total 10000 10000
C
Ca
Si
MgFe
Fe
K
AlPb
O
200 400 600 800
(a)
C
Ca
Si
MgFe Fe
K
Al
Pb
O
200 400 600 800
(b)
Figure 5 EDAX spectra from VI59B7Z sample taken on the surface (a) and cross section (b)
Journal of Spectroscopy 5
4 Discussion
The presence of the calcium oxide and hydroxide on theinternal and external surfaces of the samples as well as thecontemporary absence in the analysis of the cross sectionsand in the cracks strongly suggests that the calciumhydroxidewas not accidental on the surface but on the contrary it wasspread intentionally over both the surfaces of the potteries
On the other hand the use of limewash as binder of differ-ent pigments is widely proved and accepted in antiquities andin particular in ancient Roman walls [21 28 29] Accordingto Vitruvius intonaco is a set of finishing layers composedof lime and very fine-grained sand In this technique thecalcareous rock (mainly constituted by calcium carbonate(CaCO
3
)) is first selected in base to their purity (smallimpurity can vary the final color of the powder) then washeated in oven at high temperature (more than 1000∘C) Inthese conditions the calcium carbonate degrades in calciumoxide and carbon dioxide [21]
CaCO3(S) + heat 997888rarr CaO
(S) + CO2(G) (1)
Then the calcium oxide was mixed with water formingcalcium hydroxide
CaO3(S) +H2O 997888rarr Ca (OH)
2
(2)
Finally this compound (calcium oxidehydroxide) wasmixed again with calcium carbonate to obtain the so-calledintonaco that was applied to the wall in order to obtaina smooth polished surface that resembles marble To thiscompound often mineral pigments were added to formdifferent color on the wall Different works based on Ramanspectroscopy reveal the ill resolved double at 710ndash790 cmminus1due to the calcium oxidehydroxide plus a narrow band at1085 cmminus1 from the calcium carbonate
Some general and additional information can be deducedfrom the study of the Raman spectra of the intonaco actuallythe presence of the band from calcium carbonate is a clearindication that the samples were treated at high temperatureactually as previously stated at high temperature (above550∘C) calcium carbonate passes in calcium oxide (plusgaseous CO
2
) that being highly hygroscopic forms naturallythe calcium oxidehydroxide (CaO(OH)) In general whenthe samples were treated at relative low temperature boththe Raman signals from calcium carbonate and calciumoxidehydroxide are present as in the case of Roman muralpaints being the mural paint not thermal treated On thecontrary in our samples the absence of the band of carbonateas reported in Figures 4(a) and 4(b) can be used as anindication of a thermal treatment of the pottery samples athigh temperature
An interesting proof of the above mentioned heat effectis evident in the Raman spectra of the mural samples (casadel marinaio) Both of them refer to mural paintings fromPompeii but only the first of them (sampleHT)was in contactwith the high temperature generated by Vesuviusrsquos eruptionand the Raman signal from this sample does not presentthe peak at 1085 cmminus1 while the second sample (sample LT)pertains to a wall that was about three meters under the
Raman shift (cmminus1)
Inte
nsity
(au
)
1086 cmminus1
1200 1150 1100 1050 1000
Not exposed to eruptionExposed to eruption
Figure 6 Raman spectra taken on mural samples from casadel marinaio (Pompeii) exposed and not exposed to Vesuviusrsquoseruption The band position relative to the strongest Raman bandfrom the calcium carbonate is evidenced
ground level at the time of the eruption so the temperaturewas much lower and the calcium carbonate over the muralpainting was preserved (Figure 6)
On the contrary in the pottery samples from Pompeii(see the spectra from the VII59B11 VI 59B7Z samples asrepresentative in Figure 4) the band at 1085 cmminus1 is alwaysabsent in all the measurements performed suggesting thatthe limewash was spread over the pottery before the heattreatment in the furnace As further indication of this hypoth-esiswe report theRaman spectrumof the sample 659 A14730a clear waste of production (Figure 7) Again the band at780 cmminus1 is evident while the band of calcium carbonate isabsentThe spectrum of the jumble registered in cross sectiondoes not reveal any peak of this phase suggesting again thatthe limewash (calcium oxidehydroxide) was spread over thesurface before the heating treatment
It can be interesting to try to answer the question whichis the function of the calcium oxidehydroxide and why itwas spread over the surface of the pottery before the heattreatment
One hypothesis can be related to the same reason of themural painting that is to smooth the surfaces and to use theintonaco as a binder of the inorganic pigment (that need athermal treatment)
A secondhypothesis can be associated to an improvementto the normal cooking process of the pottery Actually theaddition of calcium oxidehydroxide creates a layer overthe surfaces that during the heat treatment remains highlyoxygenatedThe oxygen preserves the surfaces from carbona-ceous waste that blacken the final good moreover the oxygenpermits to obtain a relative higher temperature at the surfacesfavoring the vitrification process of the aluminosilicates
6 Journal of Spectroscopy
Raman shift (cmminus1)
1400 1200 1000 800 600 400
Cross sectionExternal
659 A14730
Inte
nsity
(au
)
Figure 7 Raman spectrumof the sample 659A14730 a clearwaste ofproduction of the furnace VII taken along the internal and externalsurfaces
the hardening of the clay and decreasing the porosity of thesurfaces [30 31]
The high oxygenated ambient of these samples is indi-rectly suggested from the presence of TiO
2
in the anataseforms Actually at temperature higher than 600∘C theanatase phase naturally transforms to the more stable rutilephase however highly oxygenated environmental conditionsincrease the temperature threshold for the phase transforma-tion up to 1000∘C [26]
As experimental proof of the thesis just illustrated withthe help of deconvolutions with lorentzian profiles it ispossible to analyze the Raman spectra in order to identify adegree of carbonation of the samples and then deep inside tothe absorption process of CO
2
during the heat treatment ofthe pottery and justify the use of calcium hydroxide as getterof the carbon dioxide produced during the heat treatmentAs indicated in [32 33] the method of the carbonic dioxidesequestration (CDS) is well kwon and used especially inthe case of the mineral carbonation of calcined calciumhydroxide (limewash) as indicated in the reaction
Ca (OH)2(S) + CO2 997888rarr CaCO
3(S) +H2O (3)
In the case of heat treated pottery thementioned reactiontakes place during the cooling process when the formationof calcium carbonate is allowed Calcium carbonate canassume different crystalline phases as indicated by [11 34]The principal structures are indicated in Table 2 with Ramanband and assignations
Moreover if the time of cooling is too fast it is possible tofind a mixture of mentioned phases with an high probabilityto obtain the compound in amorphous conditions [12 33 35]
The deconvolution illustrates the effective position ofthe experimental Raman bands in the spectra collectedon the ancient potteries (Figure 8 reports as example
the deconvolution from the sample 659 A14730 waste of pro-duction) Raman bands are centered at 705 cmminus1 787 cmminus1863 cmminus1 1137 cmminus1 and 1549 cmminus1 An assignation of thepeaks at 705 cmminus1 863 cmminus1 and 1137 cmminus1 is possible withthe indications of Table 2 while the band at 787 cmminus1 and1550 cmminus1 can be assigned to calcium oxidehydroxide andvibration of hydroxyl molecule (O-H out of plane bendingmode) respectively [15 16]
The band at 705 cmminus1 in particular could be assigned toAragonite phase of calcium carbonate The band at 863 cmminus1can be assigned to the ]
2
mode of (CO3
)2minus which is Ramanforbidden in the free ion but remains weak after coupling tothe cations in the lattice [8 34] The broad band at 1137 cmminus1can be assigned to the ]
1
mode due to the symmetricstretching vibration of the carbonate groups [15 16]
The presence in the spectrum of the bands assigned toAragonite and carbonate groupsweakly bonded to the cationsis significant for the happened sequestration of CO
2
by thesamples during the heat treatment
To better understand this phenomenon it is possible toexplain each singular step of the process of carbonationin clays by using experimental archeological methods andreproducing the behavior of the sample
Figure 9(a) shows the Raman spectrum of amorphouscalcium hydroxide Ca(OH)
2
obtained heating calcite pow-ders at the temperature of 1000∘C for 1 h with a ramp oftemperature of 2∘Cmin and after it reached the ambienttemperature mixed with water No other peaks assignableto other stable or metastable crystallographic phases werefound
The bands at 796 cmminus1 913 cmminus1 1187 cmminus1 and1650 cmminus1 are associated to calcium hydroxide and water asindicated by [23 34] In particular the band at 913 cmminus1 couldbe assigned to O-H out of plane bending mode according toBuzgar and Apopei [34]
After 24 h of exposition to the content of CO2
presentin the air at ambient temperature the carbonation process
Journal of Spectroscopy 7
Table 2 (a) Fundamental vibrational modes of the carbonates according to [3 4] (b) Raman bands in some carbonates and hydroxyl-carbonates
Figure 9 Raman spectrum of calcium hydroxide obtained heating at 1000∘C CaCO3
powders
takes place and in the spectrum shown in Figure 9(b) it ispossible to observe the presence of different bands associatedto the carbon dioxide sequestration The band at 913 cmminus1disappears (the band was present in the spectrum taken atthe beginning of the process Figure 9(a)) while it is possibleto observe the presence of the band at 863 cmminus1 which couldbe associated to the mode ]
2
of the carbonate ions weaklybonded to the cations In addition a new band at 740 cmminus1can be observed and assigned to the ]
3
symmetric CO3
2minus
bendingmode inVaterite suggesting favorable conditions forthis metastable form (120583-CaCO
3
) [13]By wetting the same calcium hydroxide powders used in
the previous experiment the ldquolimewashrdquo was realized with thepurpose to reproduce the ancient technique probably used inPompeii The limewash was mixed with hematite and used tocover the surface of two samples of clay indicated as A andB differentiated by the presence of calcite into the mixture(sample A) and no presence of calcite (samples B) into
8 Journal of Spectroscopy
(A) (B)
Figure 10 Laboratory samples sample A calcite in the mixture ofthe clay sample B absence of calcite in the clay Both the sampleswere covered with Fe
Figure 11 Raman spectrumwith deconvolutions of samples (a) and(b)
the mixture (Figure 10) Each sample was treated at 1000∘Cwith the same temperature treatment used in the previouscalcite sample As shown in Figure 10 the samples B present adifferent color in the limewash covered surface
Figure 11 reports the Raman spectra of the samples A andB with the relative deconvolutions with lorentzian profiles Itis possible to observe the presence of the bands assigned tocalcium hydroxide as indicated previously the presence ofthe band around 860 cmminus1 due to CO
3
2minus weakly bonded tothe cations and the presence of the band at 705 cmminus1 typicalfor the ]
4
frequency mode of carbonate in Aragonite phase[9]
Figure 12 reports the Raman spectrum of the sampleA collected in a cross section of the sample not exposedto the atmosphere at high temperature In this case the
Raman shift (cmminus1)
Inte
nsity
(au
)
18002000 1600 1400 1200 1000 800 600 400 200
Correlation factor (R) = 0993
Figure 12 Raman spectrum of the cross section of sample A
calcite present into the clay mixture has been transformedin calcium oxidehydroxide due to the high temperature andthe residual humidity of the clay From the analysis of theRaman spectrum it is possible to observe the phenomenonof carbonation as indicated by the absence of the band at705 cmminus1 (Aragonite phase) and a slow contribution of theband at 860 cmminus1 is shown (associated to the presence ofcarbonate ions weakly bonded to the cations) [9]
These results seems to indicate an high degree of knowl-edge of the cooking process of the pottery in the Romanage and in particular the use of calcium hydroxide as a toolto reduce the content of CO
2
in the furnace atmosphereand then obtain a more oxidant ambient and reach highertemperature close to the at the pottery surfaces
5 Conclusions
In this study a characterization of different type of potterysamples and painted fragments of wall belonging to Pompeiihas been performed by means of EDS microanalysis andRaman spectroscopy The principal results obtained concernthe use of calcium hydroxide above the surface of analyzedsamples before cooking the clay This technique of surfacetreatment seems to be not justified only for the use of avitrification additive or sealant but through this study it ispossible to suggest that calcium hydroxide could be used asldquogetterrdquo of CO
2
during the heat treatment The result of thisoperation is to reduce the content of CO
2
in the furnaceatmosphere and then obtain a more oxidant ambient whencooking the pottery In these conditions as illustrated in thisstudy the metallic oxides used as pigments on the surfaceor contained in the clay mixture could be preserved in thehigher state of oxidation providing a better esthetical result(in terms of color)
In any case these findings give new light on the potterymanufacturing techniques of Romans and in particular opennew questions about the real degree of knowledge of the
Journal of Spectroscopy 9
Romans about the art of ceramics and more general aboutchemistry and technologies
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This study has been supported by the Italian Ministryof University and Scientific Research (MIUR) within thenational grant ldquoFuturo in Ricercardquo 2012 TIME THROUGHCOLOURS Analysis of painted artifacts in their archaeolog-ical historical and sociological contexts (RBFR12405A 002)
References
[1] S P Koob ldquoThe use of Paraloid B-72 as an adhesive itsapplication for archaeological ceramics and other materialsrdquoStudies in Conservation vol 31 no 1 pp 7ndash14 1986
[2] S Chapman and D Mason ldquoLiterature review the use ofParaloid B-72 as a surface consolidant for stained glassrdquo JournalofTheAmerican Institute for Conservation vol 42 no 2 pp 381ndash392 2003
[3] L Burgio and R J H Clark ldquoLibrary of FT-Raman spectraof pigments minerals pigment media and varnishes andsupplement to existing library of Raman spectra of pigmentswith visible excitationrdquo Spectrochimica Acta Part A Molecularand Biomolecular Spectroscopy vol 57 no 7 pp 1491ndash1521 2001
[4] F A Cotton Chemical Applications of Group Theory Wiley-Interscience Richardson Tex USA 3rd edition 1990
[5] S Gunasekaran G Anbalagan and S Pandi ldquoRaman andinfrared spectra of carbonates of calcite structurerdquo Journal ofRaman Spectroscopy vol 37 no 9 pp 892ndash899 2006
[6] N Koura S Kohara K Takeuchi et al ldquoAlkali carbonatesRaman spectroscopy ab initio calculations and structurerdquoJournal of Molecular Structure vol 382 no 3 pp 163ndash169 1996
[7] E Mattei G de Vivo A de Santis C Gaetani C Pelosiand U Santamaria ldquoRaman spectroscopic analysis of azuriteblackeningrdquo Journal of Raman Spectroscopy vol 39 no 2 pp302ndash306 2008
[8] E B Scheetz and B W White ldquoVibrational spectra of thealkaline earth double carbonatesrdquo American Mineralogist vol62 pp 36ndash50 1977
[9] J E Parker S P Thompson A R Lennie J Potter andC C Tang ldquoA study of the aragonite-calcite transformationusingRaman spectroscopy synchrotron powder diffraction andscanning electron microscopyrdquo CrystEngComm vol 12 no 5pp 1590ndash1599 2010
[10] D Krishnamurti ldquoThe Raman spectra of aragonite strontianiteand witheriterdquo Proceedings of the Indian Academy of Sciences Avol 51 no 6 pp 285ndash295 1960
[11] J Urmos S K Sharma and F T Mackenzie ldquoCharacterizationof some biogenic carbonates with Raman spectroscopyrdquo Amer-ican Mineralogist vol 76 no 3-4 pp 641ndash646 1991
[12] M Charles R Jeanloz and R J Hemley ldquoSpectroscopic andx-ray diffraction studies of metastable crystalline-amorphoustransitions in Ca(OH)
2
and serpentinerdquo Geophysical Mono-graph Series vol 67 pp 485ndash492 1992
[13] R W Gauldie S K Sharma and E Volk ldquoMicro-Ramanspectral study of vaterite and aragonite otoliths of the cohosalmon Oncorhynchus kisutchrdquo Comparative Biochemistry andPhysiology A vol 118 no 3 pp 753ndash757 1997
[14] R L Frost W N Martens L Rintoul E Mahmutagic andJ T Kloprogge ldquoRaman spectroscopic study of azurite andmalachite at 298 and 77 Krdquo Journal of Raman Spectroscopy vol33 no 4 pp 252ndash259 2002
[15] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons New York NY USA1997
[16] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons Hoboken NJ USA6th edition 2009
[17] G D Smith and R J H Clark ldquoRaman microscopy inarchaeological sciencerdquo Journal of Archaeological Science vol 31no 8 pp 1137ndash1160 2004
[18] D Bersani and J M Madariaga ldquoApplications of Raman spec-troscopy in art and archaeologyrdquo Journal of Raman Spectroscopyvol 43 no 11 pp 1523ndash1528 2012
[19] L Stagi J A De Toro A Ardu et al ldquoSurface effects undervisible irradiation and heat treatment on the phase stability of120574-Fe2
O3
nanoparticles and 120574-Fe2
O3
-SiO2
core-shell nanostruc-turesrdquo The Journal of Physical Chemistry C vol 118 no 5 pp2857ndash2866 2014
[20] D Hradil T Grygar J Hradilova and P Bezdicka ldquoClay andiron oxide pigments in the history of paintingrdquo Applied ClayScience vol 22 no 5 pp 223ndash236 2003
[21] I Aliatis D Bersani E Campani et al ldquoPigments used inRoman wall paintings in the Vesuvian areardquo Journal of RamanSpectroscopy vol 41 no 11 pp 1537ndash1542 2010
[22] H GM Edwards DW Farwell D L A de Faria et al ldquoRamanspectroscopic study of 3000minusyearminusold human skeletal remainsfrom a sambaqui Santa Catarina Brazilrdquo Journal of RamanSpectroscopy vol 32 no 1 pp 17ndash22 2001
[23] T Y Kwon T Fujishima and Y Imai ldquoFT-Raman spectroscopyof calcium hydroxide medicament in root canalsrdquo InternationalEndodontic Journal vol 37 no 7 pp 489ndash493 2004
[24] R L Frost ldquoFourier transform Raman spectroscopy of kaolin-ite dickite and halloysiterdquo Clays amp Clay Minerals vol 43 no 2pp 191ndash195 1995
[25] I C Freestone ldquoApplications and potential of electron probemicro analysis in technological and provenance investigationsof ancient ceramicsrdquo Archaeometry vol 24 no 2 pp 99ndash1161982
[26] P C Ricci C M Carbonaro L Stagi et al ldquoAnatase-to-rutilephase transition in TiO
2
nanoparticles irradiated by visiblelightrdquo Journal of Physical Chemistry C vol 117 no 15 pp 7850ndash7857 2013
[27] P C Ricci A Casu M Salis R Corpino and A AneddaldquoOptically controlled phase variation of TiO
2
nanoparticlesrdquoJournal of Physical Chemistry C vol 114 no 34 pp 14441ndash144452010
[28] S Sanchez-Moral L Luque J-C Canaveras V Soler J Garcia-Guinea and A Aparicio ldquoLime-pozzolana mortars in Romancatacombs composition structures and restorationrdquo Cementand Concrete Research vol 35 no 8 pp 1555ndash1565 2005
[29] H G M Edwards and D W Farwell ldquoThe conservationalheritage of wall paintings and buildings an FT-Raman spectro-scopic study of prehistoric Roman mediaeval and Renaissance
10 Journal of Spectroscopy
lime substrates and mortarsrdquo Journal of Raman Spectroscopyvol 39 no 8 pp 985ndash992 2008
[30] C M Sinopoli Approaches to Archaeological CeramicsSpringer Boston Mass USA 1991
[31] R Newcomb Jr Ceramic WhitewaresmdashHistory Technology andApplications Pitman Publishing New York NY USA 1947
[32] W J J Huijgen and R N J Comans ldquoCarbon dioxide seques-tration by mineral carbonation literature reviewrdquo ECN ReportECN-C-03-016 ECN 2003
[33] W Gu D W Bousfield and C P Tripp ldquoFormation of calciumcarbonate particles by direct contact of Ca(OH)
[34] N Buzgar and A I Apopei ldquoThe Raman study of certaincarbonatesrdquo Geologie vol 15 pp 97ndash112 2009
[35] S Ekbundit K Leinenweber J L Yarger J S Robinson MVerhelst-Voorhees and G H Wolf ldquoNew high-pressure phaseand pressure-induced amorphization of Ca(OH)
2
grain sizeeffectrdquo Journal of Solid State Chemistry vol 126 no 2 pp 300ndash307 1996
Figure 3 Images of the samples VII59B11 (a) VI59B7Z (b) and 659A14730 (c)
450 300
1200 1000 800 600 400
ExternalInternal
VI59B7Z
Inte
nsity
(au
)
Raman shift (cmminus1)
(a)
450600
1200 1000 800 600 400
ExternalInternal
Inte
nsity
(au
)
A A AR R
Raman shift (cmminus1)
(b)
Figure 4 Raman spectra of the external and internal surface of samples VI59B7Z (a) and VII59B11The inset in the (a) section is an enlargedview of the external surfaces of sample VI59B7Z The inset in the (b) section reports the Raman spectrum form the cross section of sampleVII59B11 The peaks are identified as TiO
2
in the anatase (indicated with A) and rutile phase (R)
and SEM images the Raman Figure 4(a) reports the Ramanspectra a large band between 600 and 900 cmminus1 centered atabout 780 cmminus1 is present in both the spectra and no otherpeaks are easily distinguishable in the spectrum relative tointernal surface On the contrary the Raman spectrum ofthe red external surface of the sample VI 59B7Z present alsopeaks at 226 292 and 411 cmminus1 assignable to the hematitephase of the iron oxide (inset Figure 4(a)) [19] Actually theuse of iron oxides in different polymorph as red pigmentsis widely stated [18 20 21] The Romans achieved differentcolours from deep red to purple through the grinding ofhematite crystals The particle size affects the colour wherevery fine particles on a nanometer scale gave purple
According to [22 23] the large peaks at 780 cmminus1 can beassigned to the presence of calcium oxide and calcium hydrox-ideAs a confirmation the EDAXanalysis (Figure 5)was takenalong the different surfaces the peaks of calcium and Ironare well evident several elements have also been detected inthe samples probably arising from natural minerals presentin the proximity of the excavation site such as quartz (SiO
2
)feldspars leucite (KAlSi
2
O6
) and kaolinite (Al2
Si2
O5
(OH)4
)[24 25]
To better observe differences between the clay and thesurface of the pottery the samples were analyzed also inthe cracks of the surfaces and in cross section the Ramanspectrum does not reveal any presence of calcium hydroxideand the EDAX analysis reveals a small and reduced presenceof calcium while the relative presence of different elementsremains almost unaltered (Table 1)
In the sample VII59B11 (furnace VII) the Raman spectrataken along the cross section randomly present peaks at395 450 517 and 635 cmminus1 (see inset in Figure 4(b)) Threeof them are easily assignable to the presence of TiO
2
inthe anatase phase while the peak at 450 cmminus1 and theenlargement of the band at 635 cmminus1 suggest the presenceof TiO
2
in the rutile phase [26 27] It is worth noting thatthese elements are present only as tracewith respect to jumbleand the relative high intensity of the Raman signal is dueto the high efficiency of these materials and phases [26 27]In most of the other samples these peaks were not observedsuggesting the random presence of titanium oxide in thestarting material Again the Raman signal arising from thesurfaces is dominated by the large by assigned to the presenceof calcium oxidehydroxide (Figure 4(b))
4 Journal of Spectroscopy
Table 1
(a)
Element Wt At 119870-ratio 119885 119860 119865
C K 1599 2876 00481 10720 02805 10005O K 3812 5146 00780 10531 01943 10003Mg K 123 109 00053 10085 04310 10012Al K 160 128 00088 09784 05614 10019Si K 304 234 00208 10079 06754 10019K K 037 020 00032 09572 08983 10257Ca K 1809 975 01643 09789 09245 10034Fe K 1015 392 00886 08913 09776 10024Pb L 1141 119 00719 09181 10189 10000Total 10000 10000
(b)
Element Wt At 119870-ratio 119885 119860 119865
C K 1526 2515 00331 10540 02058 10004O K 4131 5110 01138 10355 02661 10003Mg K 150 122 00082 09920 05523 10044Al K 683 501 00448 09625 06778 10055Si K 1460 1029 01061 09900 07328 10011K K 209 106 00183 09395 09214 10117Ca K 705 348 00638 09608 09391 10027Fe K 619 219 00537 08717 09939 10017Pb L 516 049 00315 05993 10185 10000Total 10000 10000
C
Ca
Si
MgFe
Fe
K
AlPb
O
200 400 600 800
(a)
C
Ca
Si
MgFe Fe
K
Al
Pb
O
200 400 600 800
(b)
Figure 5 EDAX spectra from VI59B7Z sample taken on the surface (a) and cross section (b)
Journal of Spectroscopy 5
4 Discussion
The presence of the calcium oxide and hydroxide on theinternal and external surfaces of the samples as well as thecontemporary absence in the analysis of the cross sectionsand in the cracks strongly suggests that the calciumhydroxidewas not accidental on the surface but on the contrary it wasspread intentionally over both the surfaces of the potteries
On the other hand the use of limewash as binder of differ-ent pigments is widely proved and accepted in antiquities andin particular in ancient Roman walls [21 28 29] Accordingto Vitruvius intonaco is a set of finishing layers composedof lime and very fine-grained sand In this technique thecalcareous rock (mainly constituted by calcium carbonate(CaCO
3
)) is first selected in base to their purity (smallimpurity can vary the final color of the powder) then washeated in oven at high temperature (more than 1000∘C) Inthese conditions the calcium carbonate degrades in calciumoxide and carbon dioxide [21]
CaCO3(S) + heat 997888rarr CaO
(S) + CO2(G) (1)
Then the calcium oxide was mixed with water formingcalcium hydroxide
CaO3(S) +H2O 997888rarr Ca (OH)
2
(2)
Finally this compound (calcium oxidehydroxide) wasmixed again with calcium carbonate to obtain the so-calledintonaco that was applied to the wall in order to obtaina smooth polished surface that resembles marble To thiscompound often mineral pigments were added to formdifferent color on the wall Different works based on Ramanspectroscopy reveal the ill resolved double at 710ndash790 cmminus1due to the calcium oxidehydroxide plus a narrow band at1085 cmminus1 from the calcium carbonate
Some general and additional information can be deducedfrom the study of the Raman spectra of the intonaco actuallythe presence of the band from calcium carbonate is a clearindication that the samples were treated at high temperatureactually as previously stated at high temperature (above550∘C) calcium carbonate passes in calcium oxide (plusgaseous CO
2
) that being highly hygroscopic forms naturallythe calcium oxidehydroxide (CaO(OH)) In general whenthe samples were treated at relative low temperature boththe Raman signals from calcium carbonate and calciumoxidehydroxide are present as in the case of Roman muralpaints being the mural paint not thermal treated On thecontrary in our samples the absence of the band of carbonateas reported in Figures 4(a) and 4(b) can be used as anindication of a thermal treatment of the pottery samples athigh temperature
An interesting proof of the above mentioned heat effectis evident in the Raman spectra of the mural samples (casadel marinaio) Both of them refer to mural paintings fromPompeii but only the first of them (sampleHT)was in contactwith the high temperature generated by Vesuviusrsquos eruptionand the Raman signal from this sample does not presentthe peak at 1085 cmminus1 while the second sample (sample LT)pertains to a wall that was about three meters under the
Raman shift (cmminus1)
Inte
nsity
(au
)
1086 cmminus1
1200 1150 1100 1050 1000
Not exposed to eruptionExposed to eruption
Figure 6 Raman spectra taken on mural samples from casadel marinaio (Pompeii) exposed and not exposed to Vesuviusrsquoseruption The band position relative to the strongest Raman bandfrom the calcium carbonate is evidenced
ground level at the time of the eruption so the temperaturewas much lower and the calcium carbonate over the muralpainting was preserved (Figure 6)
On the contrary in the pottery samples from Pompeii(see the spectra from the VII59B11 VI 59B7Z samples asrepresentative in Figure 4) the band at 1085 cmminus1 is alwaysabsent in all the measurements performed suggesting thatthe limewash was spread over the pottery before the heattreatment in the furnace As further indication of this hypoth-esiswe report theRaman spectrumof the sample 659 A14730a clear waste of production (Figure 7) Again the band at780 cmminus1 is evident while the band of calcium carbonate isabsentThe spectrum of the jumble registered in cross sectiondoes not reveal any peak of this phase suggesting again thatthe limewash (calcium oxidehydroxide) was spread over thesurface before the heating treatment
It can be interesting to try to answer the question whichis the function of the calcium oxidehydroxide and why itwas spread over the surface of the pottery before the heattreatment
One hypothesis can be related to the same reason of themural painting that is to smooth the surfaces and to use theintonaco as a binder of the inorganic pigment (that need athermal treatment)
A secondhypothesis can be associated to an improvementto the normal cooking process of the pottery Actually theaddition of calcium oxidehydroxide creates a layer overthe surfaces that during the heat treatment remains highlyoxygenatedThe oxygen preserves the surfaces from carbona-ceous waste that blacken the final good moreover the oxygenpermits to obtain a relative higher temperature at the surfacesfavoring the vitrification process of the aluminosilicates
6 Journal of Spectroscopy
Raman shift (cmminus1)
1400 1200 1000 800 600 400
Cross sectionExternal
659 A14730
Inte
nsity
(au
)
Figure 7 Raman spectrumof the sample 659A14730 a clearwaste ofproduction of the furnace VII taken along the internal and externalsurfaces
the hardening of the clay and decreasing the porosity of thesurfaces [30 31]
The high oxygenated ambient of these samples is indi-rectly suggested from the presence of TiO
2
in the anataseforms Actually at temperature higher than 600∘C theanatase phase naturally transforms to the more stable rutilephase however highly oxygenated environmental conditionsincrease the temperature threshold for the phase transforma-tion up to 1000∘C [26]
As experimental proof of the thesis just illustrated withthe help of deconvolutions with lorentzian profiles it ispossible to analyze the Raman spectra in order to identify adegree of carbonation of the samples and then deep inside tothe absorption process of CO
2
during the heat treatment ofthe pottery and justify the use of calcium hydroxide as getterof the carbon dioxide produced during the heat treatmentAs indicated in [32 33] the method of the carbonic dioxidesequestration (CDS) is well kwon and used especially inthe case of the mineral carbonation of calcined calciumhydroxide (limewash) as indicated in the reaction
Ca (OH)2(S) + CO2 997888rarr CaCO
3(S) +H2O (3)
In the case of heat treated pottery thementioned reactiontakes place during the cooling process when the formationof calcium carbonate is allowed Calcium carbonate canassume different crystalline phases as indicated by [11 34]The principal structures are indicated in Table 2 with Ramanband and assignations
Moreover if the time of cooling is too fast it is possible tofind a mixture of mentioned phases with an high probabilityto obtain the compound in amorphous conditions [12 33 35]
The deconvolution illustrates the effective position ofthe experimental Raman bands in the spectra collectedon the ancient potteries (Figure 8 reports as example
the deconvolution from the sample 659 A14730 waste of pro-duction) Raman bands are centered at 705 cmminus1 787 cmminus1863 cmminus1 1137 cmminus1 and 1549 cmminus1 An assignation of thepeaks at 705 cmminus1 863 cmminus1 and 1137 cmminus1 is possible withthe indications of Table 2 while the band at 787 cmminus1 and1550 cmminus1 can be assigned to calcium oxidehydroxide andvibration of hydroxyl molecule (O-H out of plane bendingmode) respectively [15 16]
The band at 705 cmminus1 in particular could be assigned toAragonite phase of calcium carbonate The band at 863 cmminus1can be assigned to the ]
2
mode of (CO3
)2minus which is Ramanforbidden in the free ion but remains weak after coupling tothe cations in the lattice [8 34] The broad band at 1137 cmminus1can be assigned to the ]
1
mode due to the symmetricstretching vibration of the carbonate groups [15 16]
The presence in the spectrum of the bands assigned toAragonite and carbonate groupsweakly bonded to the cationsis significant for the happened sequestration of CO
2
by thesamples during the heat treatment
To better understand this phenomenon it is possible toexplain each singular step of the process of carbonationin clays by using experimental archeological methods andreproducing the behavior of the sample
Figure 9(a) shows the Raman spectrum of amorphouscalcium hydroxide Ca(OH)
2
obtained heating calcite pow-ders at the temperature of 1000∘C for 1 h with a ramp oftemperature of 2∘Cmin and after it reached the ambienttemperature mixed with water No other peaks assignableto other stable or metastable crystallographic phases werefound
The bands at 796 cmminus1 913 cmminus1 1187 cmminus1 and1650 cmminus1 are associated to calcium hydroxide and water asindicated by [23 34] In particular the band at 913 cmminus1 couldbe assigned to O-H out of plane bending mode according toBuzgar and Apopei [34]
After 24 h of exposition to the content of CO2
presentin the air at ambient temperature the carbonation process
Journal of Spectroscopy 7
Table 2 (a) Fundamental vibrational modes of the carbonates according to [3 4] (b) Raman bands in some carbonates and hydroxyl-carbonates
Figure 9 Raman spectrum of calcium hydroxide obtained heating at 1000∘C CaCO3
powders
takes place and in the spectrum shown in Figure 9(b) it ispossible to observe the presence of different bands associatedto the carbon dioxide sequestration The band at 913 cmminus1disappears (the band was present in the spectrum taken atthe beginning of the process Figure 9(a)) while it is possibleto observe the presence of the band at 863 cmminus1 which couldbe associated to the mode ]
2
of the carbonate ions weaklybonded to the cations In addition a new band at 740 cmminus1can be observed and assigned to the ]
3
symmetric CO3
2minus
bendingmode inVaterite suggesting favorable conditions forthis metastable form (120583-CaCO
3
) [13]By wetting the same calcium hydroxide powders used in
the previous experiment the ldquolimewashrdquo was realized with thepurpose to reproduce the ancient technique probably used inPompeii The limewash was mixed with hematite and used tocover the surface of two samples of clay indicated as A andB differentiated by the presence of calcite into the mixture(sample A) and no presence of calcite (samples B) into
8 Journal of Spectroscopy
(A) (B)
Figure 10 Laboratory samples sample A calcite in the mixture ofthe clay sample B absence of calcite in the clay Both the sampleswere covered with Fe
Figure 11 Raman spectrumwith deconvolutions of samples (a) and(b)
the mixture (Figure 10) Each sample was treated at 1000∘Cwith the same temperature treatment used in the previouscalcite sample As shown in Figure 10 the samples B present adifferent color in the limewash covered surface
Figure 11 reports the Raman spectra of the samples A andB with the relative deconvolutions with lorentzian profiles Itis possible to observe the presence of the bands assigned tocalcium hydroxide as indicated previously the presence ofthe band around 860 cmminus1 due to CO
3
2minus weakly bonded tothe cations and the presence of the band at 705 cmminus1 typicalfor the ]
4
frequency mode of carbonate in Aragonite phase[9]
Figure 12 reports the Raman spectrum of the sampleA collected in a cross section of the sample not exposedto the atmosphere at high temperature In this case the
Raman shift (cmminus1)
Inte
nsity
(au
)
18002000 1600 1400 1200 1000 800 600 400 200
Correlation factor (R) = 0993
Figure 12 Raman spectrum of the cross section of sample A
calcite present into the clay mixture has been transformedin calcium oxidehydroxide due to the high temperature andthe residual humidity of the clay From the analysis of theRaman spectrum it is possible to observe the phenomenonof carbonation as indicated by the absence of the band at705 cmminus1 (Aragonite phase) and a slow contribution of theband at 860 cmminus1 is shown (associated to the presence ofcarbonate ions weakly bonded to the cations) [9]
These results seems to indicate an high degree of knowl-edge of the cooking process of the pottery in the Romanage and in particular the use of calcium hydroxide as a toolto reduce the content of CO
2
in the furnace atmosphereand then obtain a more oxidant ambient and reach highertemperature close to the at the pottery surfaces
5 Conclusions
In this study a characterization of different type of potterysamples and painted fragments of wall belonging to Pompeiihas been performed by means of EDS microanalysis andRaman spectroscopy The principal results obtained concernthe use of calcium hydroxide above the surface of analyzedsamples before cooking the clay This technique of surfacetreatment seems to be not justified only for the use of avitrification additive or sealant but through this study it ispossible to suggest that calcium hydroxide could be used asldquogetterrdquo of CO
2
during the heat treatment The result of thisoperation is to reduce the content of CO
2
in the furnaceatmosphere and then obtain a more oxidant ambient whencooking the pottery In these conditions as illustrated in thisstudy the metallic oxides used as pigments on the surfaceor contained in the clay mixture could be preserved in thehigher state of oxidation providing a better esthetical result(in terms of color)
In any case these findings give new light on the potterymanufacturing techniques of Romans and in particular opennew questions about the real degree of knowledge of the
Journal of Spectroscopy 9
Romans about the art of ceramics and more general aboutchemistry and technologies
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This study has been supported by the Italian Ministryof University and Scientific Research (MIUR) within thenational grant ldquoFuturo in Ricercardquo 2012 TIME THROUGHCOLOURS Analysis of painted artifacts in their archaeolog-ical historical and sociological contexts (RBFR12405A 002)
References
[1] S P Koob ldquoThe use of Paraloid B-72 as an adhesive itsapplication for archaeological ceramics and other materialsrdquoStudies in Conservation vol 31 no 1 pp 7ndash14 1986
[2] S Chapman and D Mason ldquoLiterature review the use ofParaloid B-72 as a surface consolidant for stained glassrdquo JournalofTheAmerican Institute for Conservation vol 42 no 2 pp 381ndash392 2003
[3] L Burgio and R J H Clark ldquoLibrary of FT-Raman spectraof pigments minerals pigment media and varnishes andsupplement to existing library of Raman spectra of pigmentswith visible excitationrdquo Spectrochimica Acta Part A Molecularand Biomolecular Spectroscopy vol 57 no 7 pp 1491ndash1521 2001
[4] F A Cotton Chemical Applications of Group Theory Wiley-Interscience Richardson Tex USA 3rd edition 1990
[5] S Gunasekaran G Anbalagan and S Pandi ldquoRaman andinfrared spectra of carbonates of calcite structurerdquo Journal ofRaman Spectroscopy vol 37 no 9 pp 892ndash899 2006
[6] N Koura S Kohara K Takeuchi et al ldquoAlkali carbonatesRaman spectroscopy ab initio calculations and structurerdquoJournal of Molecular Structure vol 382 no 3 pp 163ndash169 1996
[7] E Mattei G de Vivo A de Santis C Gaetani C Pelosiand U Santamaria ldquoRaman spectroscopic analysis of azuriteblackeningrdquo Journal of Raman Spectroscopy vol 39 no 2 pp302ndash306 2008
[8] E B Scheetz and B W White ldquoVibrational spectra of thealkaline earth double carbonatesrdquo American Mineralogist vol62 pp 36ndash50 1977
[9] J E Parker S P Thompson A R Lennie J Potter andC C Tang ldquoA study of the aragonite-calcite transformationusingRaman spectroscopy synchrotron powder diffraction andscanning electron microscopyrdquo CrystEngComm vol 12 no 5pp 1590ndash1599 2010
[10] D Krishnamurti ldquoThe Raman spectra of aragonite strontianiteand witheriterdquo Proceedings of the Indian Academy of Sciences Avol 51 no 6 pp 285ndash295 1960
[11] J Urmos S K Sharma and F T Mackenzie ldquoCharacterizationof some biogenic carbonates with Raman spectroscopyrdquo Amer-ican Mineralogist vol 76 no 3-4 pp 641ndash646 1991
[12] M Charles R Jeanloz and R J Hemley ldquoSpectroscopic andx-ray diffraction studies of metastable crystalline-amorphoustransitions in Ca(OH)
2
and serpentinerdquo Geophysical Mono-graph Series vol 67 pp 485ndash492 1992
[13] R W Gauldie S K Sharma and E Volk ldquoMicro-Ramanspectral study of vaterite and aragonite otoliths of the cohosalmon Oncorhynchus kisutchrdquo Comparative Biochemistry andPhysiology A vol 118 no 3 pp 753ndash757 1997
[14] R L Frost W N Martens L Rintoul E Mahmutagic andJ T Kloprogge ldquoRaman spectroscopic study of azurite andmalachite at 298 and 77 Krdquo Journal of Raman Spectroscopy vol33 no 4 pp 252ndash259 2002
[15] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons New York NY USA1997
[16] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons Hoboken NJ USA6th edition 2009
[17] G D Smith and R J H Clark ldquoRaman microscopy inarchaeological sciencerdquo Journal of Archaeological Science vol 31no 8 pp 1137ndash1160 2004
[18] D Bersani and J M Madariaga ldquoApplications of Raman spec-troscopy in art and archaeologyrdquo Journal of Raman Spectroscopyvol 43 no 11 pp 1523ndash1528 2012
[19] L Stagi J A De Toro A Ardu et al ldquoSurface effects undervisible irradiation and heat treatment on the phase stability of120574-Fe2
O3
nanoparticles and 120574-Fe2
O3
-SiO2
core-shell nanostruc-turesrdquo The Journal of Physical Chemistry C vol 118 no 5 pp2857ndash2866 2014
[20] D Hradil T Grygar J Hradilova and P Bezdicka ldquoClay andiron oxide pigments in the history of paintingrdquo Applied ClayScience vol 22 no 5 pp 223ndash236 2003
[21] I Aliatis D Bersani E Campani et al ldquoPigments used inRoman wall paintings in the Vesuvian areardquo Journal of RamanSpectroscopy vol 41 no 11 pp 1537ndash1542 2010
[22] H GM Edwards DW Farwell D L A de Faria et al ldquoRamanspectroscopic study of 3000minusyearminusold human skeletal remainsfrom a sambaqui Santa Catarina Brazilrdquo Journal of RamanSpectroscopy vol 32 no 1 pp 17ndash22 2001
[23] T Y Kwon T Fujishima and Y Imai ldquoFT-Raman spectroscopyof calcium hydroxide medicament in root canalsrdquo InternationalEndodontic Journal vol 37 no 7 pp 489ndash493 2004
[24] R L Frost ldquoFourier transform Raman spectroscopy of kaolin-ite dickite and halloysiterdquo Clays amp Clay Minerals vol 43 no 2pp 191ndash195 1995
[25] I C Freestone ldquoApplications and potential of electron probemicro analysis in technological and provenance investigationsof ancient ceramicsrdquo Archaeometry vol 24 no 2 pp 99ndash1161982
[26] P C Ricci C M Carbonaro L Stagi et al ldquoAnatase-to-rutilephase transition in TiO
2
nanoparticles irradiated by visiblelightrdquo Journal of Physical Chemistry C vol 117 no 15 pp 7850ndash7857 2013
[27] P C Ricci A Casu M Salis R Corpino and A AneddaldquoOptically controlled phase variation of TiO
2
nanoparticlesrdquoJournal of Physical Chemistry C vol 114 no 34 pp 14441ndash144452010
[28] S Sanchez-Moral L Luque J-C Canaveras V Soler J Garcia-Guinea and A Aparicio ldquoLime-pozzolana mortars in Romancatacombs composition structures and restorationrdquo Cementand Concrete Research vol 35 no 8 pp 1555ndash1565 2005
[29] H G M Edwards and D W Farwell ldquoThe conservationalheritage of wall paintings and buildings an FT-Raman spectro-scopic study of prehistoric Roman mediaeval and Renaissance
10 Journal of Spectroscopy
lime substrates and mortarsrdquo Journal of Raman Spectroscopyvol 39 no 8 pp 985ndash992 2008
[30] C M Sinopoli Approaches to Archaeological CeramicsSpringer Boston Mass USA 1991
[31] R Newcomb Jr Ceramic WhitewaresmdashHistory Technology andApplications Pitman Publishing New York NY USA 1947
[32] W J J Huijgen and R N J Comans ldquoCarbon dioxide seques-tration by mineral carbonation literature reviewrdquo ECN ReportECN-C-03-016 ECN 2003
[33] W Gu D W Bousfield and C P Tripp ldquoFormation of calciumcarbonate particles by direct contact of Ca(OH)
[34] N Buzgar and A I Apopei ldquoThe Raman study of certaincarbonatesrdquo Geologie vol 15 pp 97ndash112 2009
[35] S Ekbundit K Leinenweber J L Yarger J S Robinson MVerhelst-Voorhees and G H Wolf ldquoNew high-pressure phaseand pressure-induced amorphization of Ca(OH)
2
grain sizeeffectrdquo Journal of Solid State Chemistry vol 126 no 2 pp 300ndash307 1996
C K 1599 2876 00481 10720 02805 10005O K 3812 5146 00780 10531 01943 10003Mg K 123 109 00053 10085 04310 10012Al K 160 128 00088 09784 05614 10019Si K 304 234 00208 10079 06754 10019K K 037 020 00032 09572 08983 10257Ca K 1809 975 01643 09789 09245 10034Fe K 1015 392 00886 08913 09776 10024Pb L 1141 119 00719 09181 10189 10000Total 10000 10000
(b)
Element Wt At 119870-ratio 119885 119860 119865
C K 1526 2515 00331 10540 02058 10004O K 4131 5110 01138 10355 02661 10003Mg K 150 122 00082 09920 05523 10044Al K 683 501 00448 09625 06778 10055Si K 1460 1029 01061 09900 07328 10011K K 209 106 00183 09395 09214 10117Ca K 705 348 00638 09608 09391 10027Fe K 619 219 00537 08717 09939 10017Pb L 516 049 00315 05993 10185 10000Total 10000 10000
C
Ca
Si
MgFe
Fe
K
AlPb
O
200 400 600 800
(a)
C
Ca
Si
MgFe Fe
K
Al
Pb
O
200 400 600 800
(b)
Figure 5 EDAX spectra from VI59B7Z sample taken on the surface (a) and cross section (b)
Journal of Spectroscopy 5
4 Discussion
The presence of the calcium oxide and hydroxide on theinternal and external surfaces of the samples as well as thecontemporary absence in the analysis of the cross sectionsand in the cracks strongly suggests that the calciumhydroxidewas not accidental on the surface but on the contrary it wasspread intentionally over both the surfaces of the potteries
On the other hand the use of limewash as binder of differ-ent pigments is widely proved and accepted in antiquities andin particular in ancient Roman walls [21 28 29] Accordingto Vitruvius intonaco is a set of finishing layers composedof lime and very fine-grained sand In this technique thecalcareous rock (mainly constituted by calcium carbonate(CaCO
3
)) is first selected in base to their purity (smallimpurity can vary the final color of the powder) then washeated in oven at high temperature (more than 1000∘C) Inthese conditions the calcium carbonate degrades in calciumoxide and carbon dioxide [21]
CaCO3(S) + heat 997888rarr CaO
(S) + CO2(G) (1)
Then the calcium oxide was mixed with water formingcalcium hydroxide
CaO3(S) +H2O 997888rarr Ca (OH)
2
(2)
Finally this compound (calcium oxidehydroxide) wasmixed again with calcium carbonate to obtain the so-calledintonaco that was applied to the wall in order to obtaina smooth polished surface that resembles marble To thiscompound often mineral pigments were added to formdifferent color on the wall Different works based on Ramanspectroscopy reveal the ill resolved double at 710ndash790 cmminus1due to the calcium oxidehydroxide plus a narrow band at1085 cmminus1 from the calcium carbonate
Some general and additional information can be deducedfrom the study of the Raman spectra of the intonaco actuallythe presence of the band from calcium carbonate is a clearindication that the samples were treated at high temperatureactually as previously stated at high temperature (above550∘C) calcium carbonate passes in calcium oxide (plusgaseous CO
2
) that being highly hygroscopic forms naturallythe calcium oxidehydroxide (CaO(OH)) In general whenthe samples were treated at relative low temperature boththe Raman signals from calcium carbonate and calciumoxidehydroxide are present as in the case of Roman muralpaints being the mural paint not thermal treated On thecontrary in our samples the absence of the band of carbonateas reported in Figures 4(a) and 4(b) can be used as anindication of a thermal treatment of the pottery samples athigh temperature
An interesting proof of the above mentioned heat effectis evident in the Raman spectra of the mural samples (casadel marinaio) Both of them refer to mural paintings fromPompeii but only the first of them (sampleHT)was in contactwith the high temperature generated by Vesuviusrsquos eruptionand the Raman signal from this sample does not presentthe peak at 1085 cmminus1 while the second sample (sample LT)pertains to a wall that was about three meters under the
Raman shift (cmminus1)
Inte
nsity
(au
)
1086 cmminus1
1200 1150 1100 1050 1000
Not exposed to eruptionExposed to eruption
Figure 6 Raman spectra taken on mural samples from casadel marinaio (Pompeii) exposed and not exposed to Vesuviusrsquoseruption The band position relative to the strongest Raman bandfrom the calcium carbonate is evidenced
ground level at the time of the eruption so the temperaturewas much lower and the calcium carbonate over the muralpainting was preserved (Figure 6)
On the contrary in the pottery samples from Pompeii(see the spectra from the VII59B11 VI 59B7Z samples asrepresentative in Figure 4) the band at 1085 cmminus1 is alwaysabsent in all the measurements performed suggesting thatthe limewash was spread over the pottery before the heattreatment in the furnace As further indication of this hypoth-esiswe report theRaman spectrumof the sample 659 A14730a clear waste of production (Figure 7) Again the band at780 cmminus1 is evident while the band of calcium carbonate isabsentThe spectrum of the jumble registered in cross sectiondoes not reveal any peak of this phase suggesting again thatthe limewash (calcium oxidehydroxide) was spread over thesurface before the heating treatment
It can be interesting to try to answer the question whichis the function of the calcium oxidehydroxide and why itwas spread over the surface of the pottery before the heattreatment
One hypothesis can be related to the same reason of themural painting that is to smooth the surfaces and to use theintonaco as a binder of the inorganic pigment (that need athermal treatment)
A secondhypothesis can be associated to an improvementto the normal cooking process of the pottery Actually theaddition of calcium oxidehydroxide creates a layer overthe surfaces that during the heat treatment remains highlyoxygenatedThe oxygen preserves the surfaces from carbona-ceous waste that blacken the final good moreover the oxygenpermits to obtain a relative higher temperature at the surfacesfavoring the vitrification process of the aluminosilicates
6 Journal of Spectroscopy
Raman shift (cmminus1)
1400 1200 1000 800 600 400
Cross sectionExternal
659 A14730
Inte
nsity
(au
)
Figure 7 Raman spectrumof the sample 659A14730 a clearwaste ofproduction of the furnace VII taken along the internal and externalsurfaces
the hardening of the clay and decreasing the porosity of thesurfaces [30 31]
The high oxygenated ambient of these samples is indi-rectly suggested from the presence of TiO
2
in the anataseforms Actually at temperature higher than 600∘C theanatase phase naturally transforms to the more stable rutilephase however highly oxygenated environmental conditionsincrease the temperature threshold for the phase transforma-tion up to 1000∘C [26]
As experimental proof of the thesis just illustrated withthe help of deconvolutions with lorentzian profiles it ispossible to analyze the Raman spectra in order to identify adegree of carbonation of the samples and then deep inside tothe absorption process of CO
2
during the heat treatment ofthe pottery and justify the use of calcium hydroxide as getterof the carbon dioxide produced during the heat treatmentAs indicated in [32 33] the method of the carbonic dioxidesequestration (CDS) is well kwon and used especially inthe case of the mineral carbonation of calcined calciumhydroxide (limewash) as indicated in the reaction
Ca (OH)2(S) + CO2 997888rarr CaCO
3(S) +H2O (3)
In the case of heat treated pottery thementioned reactiontakes place during the cooling process when the formationof calcium carbonate is allowed Calcium carbonate canassume different crystalline phases as indicated by [11 34]The principal structures are indicated in Table 2 with Ramanband and assignations
Moreover if the time of cooling is too fast it is possible tofind a mixture of mentioned phases with an high probabilityto obtain the compound in amorphous conditions [12 33 35]
The deconvolution illustrates the effective position ofthe experimental Raman bands in the spectra collectedon the ancient potteries (Figure 8 reports as example
the deconvolution from the sample 659 A14730 waste of pro-duction) Raman bands are centered at 705 cmminus1 787 cmminus1863 cmminus1 1137 cmminus1 and 1549 cmminus1 An assignation of thepeaks at 705 cmminus1 863 cmminus1 and 1137 cmminus1 is possible withthe indications of Table 2 while the band at 787 cmminus1 and1550 cmminus1 can be assigned to calcium oxidehydroxide andvibration of hydroxyl molecule (O-H out of plane bendingmode) respectively [15 16]
The band at 705 cmminus1 in particular could be assigned toAragonite phase of calcium carbonate The band at 863 cmminus1can be assigned to the ]
2
mode of (CO3
)2minus which is Ramanforbidden in the free ion but remains weak after coupling tothe cations in the lattice [8 34] The broad band at 1137 cmminus1can be assigned to the ]
1
mode due to the symmetricstretching vibration of the carbonate groups [15 16]
The presence in the spectrum of the bands assigned toAragonite and carbonate groupsweakly bonded to the cationsis significant for the happened sequestration of CO
2
by thesamples during the heat treatment
To better understand this phenomenon it is possible toexplain each singular step of the process of carbonationin clays by using experimental archeological methods andreproducing the behavior of the sample
Figure 9(a) shows the Raman spectrum of amorphouscalcium hydroxide Ca(OH)
2
obtained heating calcite pow-ders at the temperature of 1000∘C for 1 h with a ramp oftemperature of 2∘Cmin and after it reached the ambienttemperature mixed with water No other peaks assignableto other stable or metastable crystallographic phases werefound
The bands at 796 cmminus1 913 cmminus1 1187 cmminus1 and1650 cmminus1 are associated to calcium hydroxide and water asindicated by [23 34] In particular the band at 913 cmminus1 couldbe assigned to O-H out of plane bending mode according toBuzgar and Apopei [34]
After 24 h of exposition to the content of CO2
presentin the air at ambient temperature the carbonation process
Journal of Spectroscopy 7
Table 2 (a) Fundamental vibrational modes of the carbonates according to [3 4] (b) Raman bands in some carbonates and hydroxyl-carbonates
Figure 9 Raman spectrum of calcium hydroxide obtained heating at 1000∘C CaCO3
powders
takes place and in the spectrum shown in Figure 9(b) it ispossible to observe the presence of different bands associatedto the carbon dioxide sequestration The band at 913 cmminus1disappears (the band was present in the spectrum taken atthe beginning of the process Figure 9(a)) while it is possibleto observe the presence of the band at 863 cmminus1 which couldbe associated to the mode ]
2
of the carbonate ions weaklybonded to the cations In addition a new band at 740 cmminus1can be observed and assigned to the ]
3
symmetric CO3
2minus
bendingmode inVaterite suggesting favorable conditions forthis metastable form (120583-CaCO
3
) [13]By wetting the same calcium hydroxide powders used in
the previous experiment the ldquolimewashrdquo was realized with thepurpose to reproduce the ancient technique probably used inPompeii The limewash was mixed with hematite and used tocover the surface of two samples of clay indicated as A andB differentiated by the presence of calcite into the mixture(sample A) and no presence of calcite (samples B) into
8 Journal of Spectroscopy
(A) (B)
Figure 10 Laboratory samples sample A calcite in the mixture ofthe clay sample B absence of calcite in the clay Both the sampleswere covered with Fe
Figure 11 Raman spectrumwith deconvolutions of samples (a) and(b)
the mixture (Figure 10) Each sample was treated at 1000∘Cwith the same temperature treatment used in the previouscalcite sample As shown in Figure 10 the samples B present adifferent color in the limewash covered surface
Figure 11 reports the Raman spectra of the samples A andB with the relative deconvolutions with lorentzian profiles Itis possible to observe the presence of the bands assigned tocalcium hydroxide as indicated previously the presence ofthe band around 860 cmminus1 due to CO
3
2minus weakly bonded tothe cations and the presence of the band at 705 cmminus1 typicalfor the ]
4
frequency mode of carbonate in Aragonite phase[9]
Figure 12 reports the Raman spectrum of the sampleA collected in a cross section of the sample not exposedto the atmosphere at high temperature In this case the
Raman shift (cmminus1)
Inte
nsity
(au
)
18002000 1600 1400 1200 1000 800 600 400 200
Correlation factor (R) = 0993
Figure 12 Raman spectrum of the cross section of sample A
calcite present into the clay mixture has been transformedin calcium oxidehydroxide due to the high temperature andthe residual humidity of the clay From the analysis of theRaman spectrum it is possible to observe the phenomenonof carbonation as indicated by the absence of the band at705 cmminus1 (Aragonite phase) and a slow contribution of theband at 860 cmminus1 is shown (associated to the presence ofcarbonate ions weakly bonded to the cations) [9]
These results seems to indicate an high degree of knowl-edge of the cooking process of the pottery in the Romanage and in particular the use of calcium hydroxide as a toolto reduce the content of CO
2
in the furnace atmosphereand then obtain a more oxidant ambient and reach highertemperature close to the at the pottery surfaces
5 Conclusions
In this study a characterization of different type of potterysamples and painted fragments of wall belonging to Pompeiihas been performed by means of EDS microanalysis andRaman spectroscopy The principal results obtained concernthe use of calcium hydroxide above the surface of analyzedsamples before cooking the clay This technique of surfacetreatment seems to be not justified only for the use of avitrification additive or sealant but through this study it ispossible to suggest that calcium hydroxide could be used asldquogetterrdquo of CO
2
during the heat treatment The result of thisoperation is to reduce the content of CO
2
in the furnaceatmosphere and then obtain a more oxidant ambient whencooking the pottery In these conditions as illustrated in thisstudy the metallic oxides used as pigments on the surfaceor contained in the clay mixture could be preserved in thehigher state of oxidation providing a better esthetical result(in terms of color)
In any case these findings give new light on the potterymanufacturing techniques of Romans and in particular opennew questions about the real degree of knowledge of the
Journal of Spectroscopy 9
Romans about the art of ceramics and more general aboutchemistry and technologies
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This study has been supported by the Italian Ministryof University and Scientific Research (MIUR) within thenational grant ldquoFuturo in Ricercardquo 2012 TIME THROUGHCOLOURS Analysis of painted artifacts in their archaeolog-ical historical and sociological contexts (RBFR12405A 002)
References
[1] S P Koob ldquoThe use of Paraloid B-72 as an adhesive itsapplication for archaeological ceramics and other materialsrdquoStudies in Conservation vol 31 no 1 pp 7ndash14 1986
[2] S Chapman and D Mason ldquoLiterature review the use ofParaloid B-72 as a surface consolidant for stained glassrdquo JournalofTheAmerican Institute for Conservation vol 42 no 2 pp 381ndash392 2003
[3] L Burgio and R J H Clark ldquoLibrary of FT-Raman spectraof pigments minerals pigment media and varnishes andsupplement to existing library of Raman spectra of pigmentswith visible excitationrdquo Spectrochimica Acta Part A Molecularand Biomolecular Spectroscopy vol 57 no 7 pp 1491ndash1521 2001
[4] F A Cotton Chemical Applications of Group Theory Wiley-Interscience Richardson Tex USA 3rd edition 1990
[5] S Gunasekaran G Anbalagan and S Pandi ldquoRaman andinfrared spectra of carbonates of calcite structurerdquo Journal ofRaman Spectroscopy vol 37 no 9 pp 892ndash899 2006
[6] N Koura S Kohara K Takeuchi et al ldquoAlkali carbonatesRaman spectroscopy ab initio calculations and structurerdquoJournal of Molecular Structure vol 382 no 3 pp 163ndash169 1996
[7] E Mattei G de Vivo A de Santis C Gaetani C Pelosiand U Santamaria ldquoRaman spectroscopic analysis of azuriteblackeningrdquo Journal of Raman Spectroscopy vol 39 no 2 pp302ndash306 2008
[8] E B Scheetz and B W White ldquoVibrational spectra of thealkaline earth double carbonatesrdquo American Mineralogist vol62 pp 36ndash50 1977
[9] J E Parker S P Thompson A R Lennie J Potter andC C Tang ldquoA study of the aragonite-calcite transformationusingRaman spectroscopy synchrotron powder diffraction andscanning electron microscopyrdquo CrystEngComm vol 12 no 5pp 1590ndash1599 2010
[10] D Krishnamurti ldquoThe Raman spectra of aragonite strontianiteand witheriterdquo Proceedings of the Indian Academy of Sciences Avol 51 no 6 pp 285ndash295 1960
[11] J Urmos S K Sharma and F T Mackenzie ldquoCharacterizationof some biogenic carbonates with Raman spectroscopyrdquo Amer-ican Mineralogist vol 76 no 3-4 pp 641ndash646 1991
[12] M Charles R Jeanloz and R J Hemley ldquoSpectroscopic andx-ray diffraction studies of metastable crystalline-amorphoustransitions in Ca(OH)
2
and serpentinerdquo Geophysical Mono-graph Series vol 67 pp 485ndash492 1992
[13] R W Gauldie S K Sharma and E Volk ldquoMicro-Ramanspectral study of vaterite and aragonite otoliths of the cohosalmon Oncorhynchus kisutchrdquo Comparative Biochemistry andPhysiology A vol 118 no 3 pp 753ndash757 1997
[14] R L Frost W N Martens L Rintoul E Mahmutagic andJ T Kloprogge ldquoRaman spectroscopic study of azurite andmalachite at 298 and 77 Krdquo Journal of Raman Spectroscopy vol33 no 4 pp 252ndash259 2002
[15] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons New York NY USA1997
[16] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons Hoboken NJ USA6th edition 2009
[17] G D Smith and R J H Clark ldquoRaman microscopy inarchaeological sciencerdquo Journal of Archaeological Science vol 31no 8 pp 1137ndash1160 2004
[18] D Bersani and J M Madariaga ldquoApplications of Raman spec-troscopy in art and archaeologyrdquo Journal of Raman Spectroscopyvol 43 no 11 pp 1523ndash1528 2012
[19] L Stagi J A De Toro A Ardu et al ldquoSurface effects undervisible irradiation and heat treatment on the phase stability of120574-Fe2
O3
nanoparticles and 120574-Fe2
O3
-SiO2
core-shell nanostruc-turesrdquo The Journal of Physical Chemistry C vol 118 no 5 pp2857ndash2866 2014
[20] D Hradil T Grygar J Hradilova and P Bezdicka ldquoClay andiron oxide pigments in the history of paintingrdquo Applied ClayScience vol 22 no 5 pp 223ndash236 2003
[21] I Aliatis D Bersani E Campani et al ldquoPigments used inRoman wall paintings in the Vesuvian areardquo Journal of RamanSpectroscopy vol 41 no 11 pp 1537ndash1542 2010
[22] H GM Edwards DW Farwell D L A de Faria et al ldquoRamanspectroscopic study of 3000minusyearminusold human skeletal remainsfrom a sambaqui Santa Catarina Brazilrdquo Journal of RamanSpectroscopy vol 32 no 1 pp 17ndash22 2001
[23] T Y Kwon T Fujishima and Y Imai ldquoFT-Raman spectroscopyof calcium hydroxide medicament in root canalsrdquo InternationalEndodontic Journal vol 37 no 7 pp 489ndash493 2004
[24] R L Frost ldquoFourier transform Raman spectroscopy of kaolin-ite dickite and halloysiterdquo Clays amp Clay Minerals vol 43 no 2pp 191ndash195 1995
[25] I C Freestone ldquoApplications and potential of electron probemicro analysis in technological and provenance investigationsof ancient ceramicsrdquo Archaeometry vol 24 no 2 pp 99ndash1161982
[26] P C Ricci C M Carbonaro L Stagi et al ldquoAnatase-to-rutilephase transition in TiO
2
nanoparticles irradiated by visiblelightrdquo Journal of Physical Chemistry C vol 117 no 15 pp 7850ndash7857 2013
[27] P C Ricci A Casu M Salis R Corpino and A AneddaldquoOptically controlled phase variation of TiO
2
nanoparticlesrdquoJournal of Physical Chemistry C vol 114 no 34 pp 14441ndash144452010
[28] S Sanchez-Moral L Luque J-C Canaveras V Soler J Garcia-Guinea and A Aparicio ldquoLime-pozzolana mortars in Romancatacombs composition structures and restorationrdquo Cementand Concrete Research vol 35 no 8 pp 1555ndash1565 2005
[29] H G M Edwards and D W Farwell ldquoThe conservationalheritage of wall paintings and buildings an FT-Raman spectro-scopic study of prehistoric Roman mediaeval and Renaissance
10 Journal of Spectroscopy
lime substrates and mortarsrdquo Journal of Raman Spectroscopyvol 39 no 8 pp 985ndash992 2008
[30] C M Sinopoli Approaches to Archaeological CeramicsSpringer Boston Mass USA 1991
[31] R Newcomb Jr Ceramic WhitewaresmdashHistory Technology andApplications Pitman Publishing New York NY USA 1947
[32] W J J Huijgen and R N J Comans ldquoCarbon dioxide seques-tration by mineral carbonation literature reviewrdquo ECN ReportECN-C-03-016 ECN 2003
[33] W Gu D W Bousfield and C P Tripp ldquoFormation of calciumcarbonate particles by direct contact of Ca(OH)
[34] N Buzgar and A I Apopei ldquoThe Raman study of certaincarbonatesrdquo Geologie vol 15 pp 97ndash112 2009
[35] S Ekbundit K Leinenweber J L Yarger J S Robinson MVerhelst-Voorhees and G H Wolf ldquoNew high-pressure phaseand pressure-induced amorphization of Ca(OH)
2
grain sizeeffectrdquo Journal of Solid State Chemistry vol 126 no 2 pp 300ndash307 1996
The presence of the calcium oxide and hydroxide on theinternal and external surfaces of the samples as well as thecontemporary absence in the analysis of the cross sectionsand in the cracks strongly suggests that the calciumhydroxidewas not accidental on the surface but on the contrary it wasspread intentionally over both the surfaces of the potteries
On the other hand the use of limewash as binder of differ-ent pigments is widely proved and accepted in antiquities andin particular in ancient Roman walls [21 28 29] Accordingto Vitruvius intonaco is a set of finishing layers composedof lime and very fine-grained sand In this technique thecalcareous rock (mainly constituted by calcium carbonate(CaCO
3
)) is first selected in base to their purity (smallimpurity can vary the final color of the powder) then washeated in oven at high temperature (more than 1000∘C) Inthese conditions the calcium carbonate degrades in calciumoxide and carbon dioxide [21]
CaCO3(S) + heat 997888rarr CaO
(S) + CO2(G) (1)
Then the calcium oxide was mixed with water formingcalcium hydroxide
CaO3(S) +H2O 997888rarr Ca (OH)
2
(2)
Finally this compound (calcium oxidehydroxide) wasmixed again with calcium carbonate to obtain the so-calledintonaco that was applied to the wall in order to obtaina smooth polished surface that resembles marble To thiscompound often mineral pigments were added to formdifferent color on the wall Different works based on Ramanspectroscopy reveal the ill resolved double at 710ndash790 cmminus1due to the calcium oxidehydroxide plus a narrow band at1085 cmminus1 from the calcium carbonate
Some general and additional information can be deducedfrom the study of the Raman spectra of the intonaco actuallythe presence of the band from calcium carbonate is a clearindication that the samples were treated at high temperatureactually as previously stated at high temperature (above550∘C) calcium carbonate passes in calcium oxide (plusgaseous CO
2
) that being highly hygroscopic forms naturallythe calcium oxidehydroxide (CaO(OH)) In general whenthe samples were treated at relative low temperature boththe Raman signals from calcium carbonate and calciumoxidehydroxide are present as in the case of Roman muralpaints being the mural paint not thermal treated On thecontrary in our samples the absence of the band of carbonateas reported in Figures 4(a) and 4(b) can be used as anindication of a thermal treatment of the pottery samples athigh temperature
An interesting proof of the above mentioned heat effectis evident in the Raman spectra of the mural samples (casadel marinaio) Both of them refer to mural paintings fromPompeii but only the first of them (sampleHT)was in contactwith the high temperature generated by Vesuviusrsquos eruptionand the Raman signal from this sample does not presentthe peak at 1085 cmminus1 while the second sample (sample LT)pertains to a wall that was about three meters under the
Raman shift (cmminus1)
Inte
nsity
(au
)
1086 cmminus1
1200 1150 1100 1050 1000
Not exposed to eruptionExposed to eruption
Figure 6 Raman spectra taken on mural samples from casadel marinaio (Pompeii) exposed and not exposed to Vesuviusrsquoseruption The band position relative to the strongest Raman bandfrom the calcium carbonate is evidenced
ground level at the time of the eruption so the temperaturewas much lower and the calcium carbonate over the muralpainting was preserved (Figure 6)
On the contrary in the pottery samples from Pompeii(see the spectra from the VII59B11 VI 59B7Z samples asrepresentative in Figure 4) the band at 1085 cmminus1 is alwaysabsent in all the measurements performed suggesting thatthe limewash was spread over the pottery before the heattreatment in the furnace As further indication of this hypoth-esiswe report theRaman spectrumof the sample 659 A14730a clear waste of production (Figure 7) Again the band at780 cmminus1 is evident while the band of calcium carbonate isabsentThe spectrum of the jumble registered in cross sectiondoes not reveal any peak of this phase suggesting again thatthe limewash (calcium oxidehydroxide) was spread over thesurface before the heating treatment
It can be interesting to try to answer the question whichis the function of the calcium oxidehydroxide and why itwas spread over the surface of the pottery before the heattreatment
One hypothesis can be related to the same reason of themural painting that is to smooth the surfaces and to use theintonaco as a binder of the inorganic pigment (that need athermal treatment)
A secondhypothesis can be associated to an improvementto the normal cooking process of the pottery Actually theaddition of calcium oxidehydroxide creates a layer overthe surfaces that during the heat treatment remains highlyoxygenatedThe oxygen preserves the surfaces from carbona-ceous waste that blacken the final good moreover the oxygenpermits to obtain a relative higher temperature at the surfacesfavoring the vitrification process of the aluminosilicates
6 Journal of Spectroscopy
Raman shift (cmminus1)
1400 1200 1000 800 600 400
Cross sectionExternal
659 A14730
Inte
nsity
(au
)
Figure 7 Raman spectrumof the sample 659A14730 a clearwaste ofproduction of the furnace VII taken along the internal and externalsurfaces
the hardening of the clay and decreasing the porosity of thesurfaces [30 31]
The high oxygenated ambient of these samples is indi-rectly suggested from the presence of TiO
2
in the anataseforms Actually at temperature higher than 600∘C theanatase phase naturally transforms to the more stable rutilephase however highly oxygenated environmental conditionsincrease the temperature threshold for the phase transforma-tion up to 1000∘C [26]
As experimental proof of the thesis just illustrated withthe help of deconvolutions with lorentzian profiles it ispossible to analyze the Raman spectra in order to identify adegree of carbonation of the samples and then deep inside tothe absorption process of CO
2
during the heat treatment ofthe pottery and justify the use of calcium hydroxide as getterof the carbon dioxide produced during the heat treatmentAs indicated in [32 33] the method of the carbonic dioxidesequestration (CDS) is well kwon and used especially inthe case of the mineral carbonation of calcined calciumhydroxide (limewash) as indicated in the reaction
Ca (OH)2(S) + CO2 997888rarr CaCO
3(S) +H2O (3)
In the case of heat treated pottery thementioned reactiontakes place during the cooling process when the formationof calcium carbonate is allowed Calcium carbonate canassume different crystalline phases as indicated by [11 34]The principal structures are indicated in Table 2 with Ramanband and assignations
Moreover if the time of cooling is too fast it is possible tofind a mixture of mentioned phases with an high probabilityto obtain the compound in amorphous conditions [12 33 35]
The deconvolution illustrates the effective position ofthe experimental Raman bands in the spectra collectedon the ancient potteries (Figure 8 reports as example
the deconvolution from the sample 659 A14730 waste of pro-duction) Raman bands are centered at 705 cmminus1 787 cmminus1863 cmminus1 1137 cmminus1 and 1549 cmminus1 An assignation of thepeaks at 705 cmminus1 863 cmminus1 and 1137 cmminus1 is possible withthe indications of Table 2 while the band at 787 cmminus1 and1550 cmminus1 can be assigned to calcium oxidehydroxide andvibration of hydroxyl molecule (O-H out of plane bendingmode) respectively [15 16]
The band at 705 cmminus1 in particular could be assigned toAragonite phase of calcium carbonate The band at 863 cmminus1can be assigned to the ]
2
mode of (CO3
)2minus which is Ramanforbidden in the free ion but remains weak after coupling tothe cations in the lattice [8 34] The broad band at 1137 cmminus1can be assigned to the ]
1
mode due to the symmetricstretching vibration of the carbonate groups [15 16]
The presence in the spectrum of the bands assigned toAragonite and carbonate groupsweakly bonded to the cationsis significant for the happened sequestration of CO
2
by thesamples during the heat treatment
To better understand this phenomenon it is possible toexplain each singular step of the process of carbonationin clays by using experimental archeological methods andreproducing the behavior of the sample
Figure 9(a) shows the Raman spectrum of amorphouscalcium hydroxide Ca(OH)
2
obtained heating calcite pow-ders at the temperature of 1000∘C for 1 h with a ramp oftemperature of 2∘Cmin and after it reached the ambienttemperature mixed with water No other peaks assignableto other stable or metastable crystallographic phases werefound
The bands at 796 cmminus1 913 cmminus1 1187 cmminus1 and1650 cmminus1 are associated to calcium hydroxide and water asindicated by [23 34] In particular the band at 913 cmminus1 couldbe assigned to O-H out of plane bending mode according toBuzgar and Apopei [34]
After 24 h of exposition to the content of CO2
presentin the air at ambient temperature the carbonation process
Journal of Spectroscopy 7
Table 2 (a) Fundamental vibrational modes of the carbonates according to [3 4] (b) Raman bands in some carbonates and hydroxyl-carbonates
Figure 9 Raman spectrum of calcium hydroxide obtained heating at 1000∘C CaCO3
powders
takes place and in the spectrum shown in Figure 9(b) it ispossible to observe the presence of different bands associatedto the carbon dioxide sequestration The band at 913 cmminus1disappears (the band was present in the spectrum taken atthe beginning of the process Figure 9(a)) while it is possibleto observe the presence of the band at 863 cmminus1 which couldbe associated to the mode ]
2
of the carbonate ions weaklybonded to the cations In addition a new band at 740 cmminus1can be observed and assigned to the ]
3
symmetric CO3
2minus
bendingmode inVaterite suggesting favorable conditions forthis metastable form (120583-CaCO
3
) [13]By wetting the same calcium hydroxide powders used in
the previous experiment the ldquolimewashrdquo was realized with thepurpose to reproduce the ancient technique probably used inPompeii The limewash was mixed with hematite and used tocover the surface of two samples of clay indicated as A andB differentiated by the presence of calcite into the mixture(sample A) and no presence of calcite (samples B) into
8 Journal of Spectroscopy
(A) (B)
Figure 10 Laboratory samples sample A calcite in the mixture ofthe clay sample B absence of calcite in the clay Both the sampleswere covered with Fe
Figure 11 Raman spectrumwith deconvolutions of samples (a) and(b)
the mixture (Figure 10) Each sample was treated at 1000∘Cwith the same temperature treatment used in the previouscalcite sample As shown in Figure 10 the samples B present adifferent color in the limewash covered surface
Figure 11 reports the Raman spectra of the samples A andB with the relative deconvolutions with lorentzian profiles Itis possible to observe the presence of the bands assigned tocalcium hydroxide as indicated previously the presence ofthe band around 860 cmminus1 due to CO
3
2minus weakly bonded tothe cations and the presence of the band at 705 cmminus1 typicalfor the ]
4
frequency mode of carbonate in Aragonite phase[9]
Figure 12 reports the Raman spectrum of the sampleA collected in a cross section of the sample not exposedto the atmosphere at high temperature In this case the
Raman shift (cmminus1)
Inte
nsity
(au
)
18002000 1600 1400 1200 1000 800 600 400 200
Correlation factor (R) = 0993
Figure 12 Raman spectrum of the cross section of sample A
calcite present into the clay mixture has been transformedin calcium oxidehydroxide due to the high temperature andthe residual humidity of the clay From the analysis of theRaman spectrum it is possible to observe the phenomenonof carbonation as indicated by the absence of the band at705 cmminus1 (Aragonite phase) and a slow contribution of theband at 860 cmminus1 is shown (associated to the presence ofcarbonate ions weakly bonded to the cations) [9]
These results seems to indicate an high degree of knowl-edge of the cooking process of the pottery in the Romanage and in particular the use of calcium hydroxide as a toolto reduce the content of CO
2
in the furnace atmosphereand then obtain a more oxidant ambient and reach highertemperature close to the at the pottery surfaces
5 Conclusions
In this study a characterization of different type of potterysamples and painted fragments of wall belonging to Pompeiihas been performed by means of EDS microanalysis andRaman spectroscopy The principal results obtained concernthe use of calcium hydroxide above the surface of analyzedsamples before cooking the clay This technique of surfacetreatment seems to be not justified only for the use of avitrification additive or sealant but through this study it ispossible to suggest that calcium hydroxide could be used asldquogetterrdquo of CO
2
during the heat treatment The result of thisoperation is to reduce the content of CO
2
in the furnaceatmosphere and then obtain a more oxidant ambient whencooking the pottery In these conditions as illustrated in thisstudy the metallic oxides used as pigments on the surfaceor contained in the clay mixture could be preserved in thehigher state of oxidation providing a better esthetical result(in terms of color)
In any case these findings give new light on the potterymanufacturing techniques of Romans and in particular opennew questions about the real degree of knowledge of the
Journal of Spectroscopy 9
Romans about the art of ceramics and more general aboutchemistry and technologies
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This study has been supported by the Italian Ministryof University and Scientific Research (MIUR) within thenational grant ldquoFuturo in Ricercardquo 2012 TIME THROUGHCOLOURS Analysis of painted artifacts in their archaeolog-ical historical and sociological contexts (RBFR12405A 002)
References
[1] S P Koob ldquoThe use of Paraloid B-72 as an adhesive itsapplication for archaeological ceramics and other materialsrdquoStudies in Conservation vol 31 no 1 pp 7ndash14 1986
[2] S Chapman and D Mason ldquoLiterature review the use ofParaloid B-72 as a surface consolidant for stained glassrdquo JournalofTheAmerican Institute for Conservation vol 42 no 2 pp 381ndash392 2003
[3] L Burgio and R J H Clark ldquoLibrary of FT-Raman spectraof pigments minerals pigment media and varnishes andsupplement to existing library of Raman spectra of pigmentswith visible excitationrdquo Spectrochimica Acta Part A Molecularand Biomolecular Spectroscopy vol 57 no 7 pp 1491ndash1521 2001
[4] F A Cotton Chemical Applications of Group Theory Wiley-Interscience Richardson Tex USA 3rd edition 1990
[5] S Gunasekaran G Anbalagan and S Pandi ldquoRaman andinfrared spectra of carbonates of calcite structurerdquo Journal ofRaman Spectroscopy vol 37 no 9 pp 892ndash899 2006
[6] N Koura S Kohara K Takeuchi et al ldquoAlkali carbonatesRaman spectroscopy ab initio calculations and structurerdquoJournal of Molecular Structure vol 382 no 3 pp 163ndash169 1996
[7] E Mattei G de Vivo A de Santis C Gaetani C Pelosiand U Santamaria ldquoRaman spectroscopic analysis of azuriteblackeningrdquo Journal of Raman Spectroscopy vol 39 no 2 pp302ndash306 2008
[8] E B Scheetz and B W White ldquoVibrational spectra of thealkaline earth double carbonatesrdquo American Mineralogist vol62 pp 36ndash50 1977
[9] J E Parker S P Thompson A R Lennie J Potter andC C Tang ldquoA study of the aragonite-calcite transformationusingRaman spectroscopy synchrotron powder diffraction andscanning electron microscopyrdquo CrystEngComm vol 12 no 5pp 1590ndash1599 2010
[10] D Krishnamurti ldquoThe Raman spectra of aragonite strontianiteand witheriterdquo Proceedings of the Indian Academy of Sciences Avol 51 no 6 pp 285ndash295 1960
[11] J Urmos S K Sharma and F T Mackenzie ldquoCharacterizationof some biogenic carbonates with Raman spectroscopyrdquo Amer-ican Mineralogist vol 76 no 3-4 pp 641ndash646 1991
[12] M Charles R Jeanloz and R J Hemley ldquoSpectroscopic andx-ray diffraction studies of metastable crystalline-amorphoustransitions in Ca(OH)
2
and serpentinerdquo Geophysical Mono-graph Series vol 67 pp 485ndash492 1992
[13] R W Gauldie S K Sharma and E Volk ldquoMicro-Ramanspectral study of vaterite and aragonite otoliths of the cohosalmon Oncorhynchus kisutchrdquo Comparative Biochemistry andPhysiology A vol 118 no 3 pp 753ndash757 1997
[14] R L Frost W N Martens L Rintoul E Mahmutagic andJ T Kloprogge ldquoRaman spectroscopic study of azurite andmalachite at 298 and 77 Krdquo Journal of Raman Spectroscopy vol33 no 4 pp 252ndash259 2002
[15] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons New York NY USA1997
[16] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons Hoboken NJ USA6th edition 2009
[17] G D Smith and R J H Clark ldquoRaman microscopy inarchaeological sciencerdquo Journal of Archaeological Science vol 31no 8 pp 1137ndash1160 2004
[18] D Bersani and J M Madariaga ldquoApplications of Raman spec-troscopy in art and archaeologyrdquo Journal of Raman Spectroscopyvol 43 no 11 pp 1523ndash1528 2012
[19] L Stagi J A De Toro A Ardu et al ldquoSurface effects undervisible irradiation and heat treatment on the phase stability of120574-Fe2
O3
nanoparticles and 120574-Fe2
O3
-SiO2
core-shell nanostruc-turesrdquo The Journal of Physical Chemistry C vol 118 no 5 pp2857ndash2866 2014
[20] D Hradil T Grygar J Hradilova and P Bezdicka ldquoClay andiron oxide pigments in the history of paintingrdquo Applied ClayScience vol 22 no 5 pp 223ndash236 2003
[21] I Aliatis D Bersani E Campani et al ldquoPigments used inRoman wall paintings in the Vesuvian areardquo Journal of RamanSpectroscopy vol 41 no 11 pp 1537ndash1542 2010
[22] H GM Edwards DW Farwell D L A de Faria et al ldquoRamanspectroscopic study of 3000minusyearminusold human skeletal remainsfrom a sambaqui Santa Catarina Brazilrdquo Journal of RamanSpectroscopy vol 32 no 1 pp 17ndash22 2001
[23] T Y Kwon T Fujishima and Y Imai ldquoFT-Raman spectroscopyof calcium hydroxide medicament in root canalsrdquo InternationalEndodontic Journal vol 37 no 7 pp 489ndash493 2004
[24] R L Frost ldquoFourier transform Raman spectroscopy of kaolin-ite dickite and halloysiterdquo Clays amp Clay Minerals vol 43 no 2pp 191ndash195 1995
[25] I C Freestone ldquoApplications and potential of electron probemicro analysis in technological and provenance investigationsof ancient ceramicsrdquo Archaeometry vol 24 no 2 pp 99ndash1161982
[26] P C Ricci C M Carbonaro L Stagi et al ldquoAnatase-to-rutilephase transition in TiO
2
nanoparticles irradiated by visiblelightrdquo Journal of Physical Chemistry C vol 117 no 15 pp 7850ndash7857 2013
[27] P C Ricci A Casu M Salis R Corpino and A AneddaldquoOptically controlled phase variation of TiO
2
nanoparticlesrdquoJournal of Physical Chemistry C vol 114 no 34 pp 14441ndash144452010
[28] S Sanchez-Moral L Luque J-C Canaveras V Soler J Garcia-Guinea and A Aparicio ldquoLime-pozzolana mortars in Romancatacombs composition structures and restorationrdquo Cementand Concrete Research vol 35 no 8 pp 1555ndash1565 2005
[29] H G M Edwards and D W Farwell ldquoThe conservationalheritage of wall paintings and buildings an FT-Raman spectro-scopic study of prehistoric Roman mediaeval and Renaissance
10 Journal of Spectroscopy
lime substrates and mortarsrdquo Journal of Raman Spectroscopyvol 39 no 8 pp 985ndash992 2008
[30] C M Sinopoli Approaches to Archaeological CeramicsSpringer Boston Mass USA 1991
[31] R Newcomb Jr Ceramic WhitewaresmdashHistory Technology andApplications Pitman Publishing New York NY USA 1947
[32] W J J Huijgen and R N J Comans ldquoCarbon dioxide seques-tration by mineral carbonation literature reviewrdquo ECN ReportECN-C-03-016 ECN 2003
[33] W Gu D W Bousfield and C P Tripp ldquoFormation of calciumcarbonate particles by direct contact of Ca(OH)
[34] N Buzgar and A I Apopei ldquoThe Raman study of certaincarbonatesrdquo Geologie vol 15 pp 97ndash112 2009
[35] S Ekbundit K Leinenweber J L Yarger J S Robinson MVerhelst-Voorhees and G H Wolf ldquoNew high-pressure phaseand pressure-induced amorphization of Ca(OH)
2
grain sizeeffectrdquo Journal of Solid State Chemistry vol 126 no 2 pp 300ndash307 1996
Figure 7 Raman spectrumof the sample 659A14730 a clearwaste ofproduction of the furnace VII taken along the internal and externalsurfaces
the hardening of the clay and decreasing the porosity of thesurfaces [30 31]
The high oxygenated ambient of these samples is indi-rectly suggested from the presence of TiO
2
in the anataseforms Actually at temperature higher than 600∘C theanatase phase naturally transforms to the more stable rutilephase however highly oxygenated environmental conditionsincrease the temperature threshold for the phase transforma-tion up to 1000∘C [26]
As experimental proof of the thesis just illustrated withthe help of deconvolutions with lorentzian profiles it ispossible to analyze the Raman spectra in order to identify adegree of carbonation of the samples and then deep inside tothe absorption process of CO
2
during the heat treatment ofthe pottery and justify the use of calcium hydroxide as getterof the carbon dioxide produced during the heat treatmentAs indicated in [32 33] the method of the carbonic dioxidesequestration (CDS) is well kwon and used especially inthe case of the mineral carbonation of calcined calciumhydroxide (limewash) as indicated in the reaction
Ca (OH)2(S) + CO2 997888rarr CaCO
3(S) +H2O (3)
In the case of heat treated pottery thementioned reactiontakes place during the cooling process when the formationof calcium carbonate is allowed Calcium carbonate canassume different crystalline phases as indicated by [11 34]The principal structures are indicated in Table 2 with Ramanband and assignations
Moreover if the time of cooling is too fast it is possible tofind a mixture of mentioned phases with an high probabilityto obtain the compound in amorphous conditions [12 33 35]
The deconvolution illustrates the effective position ofthe experimental Raman bands in the spectra collectedon the ancient potteries (Figure 8 reports as example
the deconvolution from the sample 659 A14730 waste of pro-duction) Raman bands are centered at 705 cmminus1 787 cmminus1863 cmminus1 1137 cmminus1 and 1549 cmminus1 An assignation of thepeaks at 705 cmminus1 863 cmminus1 and 1137 cmminus1 is possible withthe indications of Table 2 while the band at 787 cmminus1 and1550 cmminus1 can be assigned to calcium oxidehydroxide andvibration of hydroxyl molecule (O-H out of plane bendingmode) respectively [15 16]
The band at 705 cmminus1 in particular could be assigned toAragonite phase of calcium carbonate The band at 863 cmminus1can be assigned to the ]
2
mode of (CO3
)2minus which is Ramanforbidden in the free ion but remains weak after coupling tothe cations in the lattice [8 34] The broad band at 1137 cmminus1can be assigned to the ]
1
mode due to the symmetricstretching vibration of the carbonate groups [15 16]
The presence in the spectrum of the bands assigned toAragonite and carbonate groupsweakly bonded to the cationsis significant for the happened sequestration of CO
2
by thesamples during the heat treatment
To better understand this phenomenon it is possible toexplain each singular step of the process of carbonationin clays by using experimental archeological methods andreproducing the behavior of the sample
Figure 9(a) shows the Raman spectrum of amorphouscalcium hydroxide Ca(OH)
2
obtained heating calcite pow-ders at the temperature of 1000∘C for 1 h with a ramp oftemperature of 2∘Cmin and after it reached the ambienttemperature mixed with water No other peaks assignableto other stable or metastable crystallographic phases werefound
The bands at 796 cmminus1 913 cmminus1 1187 cmminus1 and1650 cmminus1 are associated to calcium hydroxide and water asindicated by [23 34] In particular the band at 913 cmminus1 couldbe assigned to O-H out of plane bending mode according toBuzgar and Apopei [34]
After 24 h of exposition to the content of CO2
presentin the air at ambient temperature the carbonation process
Journal of Spectroscopy 7
Table 2 (a) Fundamental vibrational modes of the carbonates according to [3 4] (b) Raman bands in some carbonates and hydroxyl-carbonates
Figure 9 Raman spectrum of calcium hydroxide obtained heating at 1000∘C CaCO3
powders
takes place and in the spectrum shown in Figure 9(b) it ispossible to observe the presence of different bands associatedto the carbon dioxide sequestration The band at 913 cmminus1disappears (the band was present in the spectrum taken atthe beginning of the process Figure 9(a)) while it is possibleto observe the presence of the band at 863 cmminus1 which couldbe associated to the mode ]
2
of the carbonate ions weaklybonded to the cations In addition a new band at 740 cmminus1can be observed and assigned to the ]
3
symmetric CO3
2minus
bendingmode inVaterite suggesting favorable conditions forthis metastable form (120583-CaCO
3
) [13]By wetting the same calcium hydroxide powders used in
the previous experiment the ldquolimewashrdquo was realized with thepurpose to reproduce the ancient technique probably used inPompeii The limewash was mixed with hematite and used tocover the surface of two samples of clay indicated as A andB differentiated by the presence of calcite into the mixture(sample A) and no presence of calcite (samples B) into
8 Journal of Spectroscopy
(A) (B)
Figure 10 Laboratory samples sample A calcite in the mixture ofthe clay sample B absence of calcite in the clay Both the sampleswere covered with Fe
Figure 11 Raman spectrumwith deconvolutions of samples (a) and(b)
the mixture (Figure 10) Each sample was treated at 1000∘Cwith the same temperature treatment used in the previouscalcite sample As shown in Figure 10 the samples B present adifferent color in the limewash covered surface
Figure 11 reports the Raman spectra of the samples A andB with the relative deconvolutions with lorentzian profiles Itis possible to observe the presence of the bands assigned tocalcium hydroxide as indicated previously the presence ofthe band around 860 cmminus1 due to CO
3
2minus weakly bonded tothe cations and the presence of the band at 705 cmminus1 typicalfor the ]
4
frequency mode of carbonate in Aragonite phase[9]
Figure 12 reports the Raman spectrum of the sampleA collected in a cross section of the sample not exposedto the atmosphere at high temperature In this case the
Raman shift (cmminus1)
Inte
nsity
(au
)
18002000 1600 1400 1200 1000 800 600 400 200
Correlation factor (R) = 0993
Figure 12 Raman spectrum of the cross section of sample A
calcite present into the clay mixture has been transformedin calcium oxidehydroxide due to the high temperature andthe residual humidity of the clay From the analysis of theRaman spectrum it is possible to observe the phenomenonof carbonation as indicated by the absence of the band at705 cmminus1 (Aragonite phase) and a slow contribution of theband at 860 cmminus1 is shown (associated to the presence ofcarbonate ions weakly bonded to the cations) [9]
These results seems to indicate an high degree of knowl-edge of the cooking process of the pottery in the Romanage and in particular the use of calcium hydroxide as a toolto reduce the content of CO
2
in the furnace atmosphereand then obtain a more oxidant ambient and reach highertemperature close to the at the pottery surfaces
5 Conclusions
In this study a characterization of different type of potterysamples and painted fragments of wall belonging to Pompeiihas been performed by means of EDS microanalysis andRaman spectroscopy The principal results obtained concernthe use of calcium hydroxide above the surface of analyzedsamples before cooking the clay This technique of surfacetreatment seems to be not justified only for the use of avitrification additive or sealant but through this study it ispossible to suggest that calcium hydroxide could be used asldquogetterrdquo of CO
2
during the heat treatment The result of thisoperation is to reduce the content of CO
2
in the furnaceatmosphere and then obtain a more oxidant ambient whencooking the pottery In these conditions as illustrated in thisstudy the metallic oxides used as pigments on the surfaceor contained in the clay mixture could be preserved in thehigher state of oxidation providing a better esthetical result(in terms of color)
In any case these findings give new light on the potterymanufacturing techniques of Romans and in particular opennew questions about the real degree of knowledge of the
Journal of Spectroscopy 9
Romans about the art of ceramics and more general aboutchemistry and technologies
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This study has been supported by the Italian Ministryof University and Scientific Research (MIUR) within thenational grant ldquoFuturo in Ricercardquo 2012 TIME THROUGHCOLOURS Analysis of painted artifacts in their archaeolog-ical historical and sociological contexts (RBFR12405A 002)
References
[1] S P Koob ldquoThe use of Paraloid B-72 as an adhesive itsapplication for archaeological ceramics and other materialsrdquoStudies in Conservation vol 31 no 1 pp 7ndash14 1986
[2] S Chapman and D Mason ldquoLiterature review the use ofParaloid B-72 as a surface consolidant for stained glassrdquo JournalofTheAmerican Institute for Conservation vol 42 no 2 pp 381ndash392 2003
[3] L Burgio and R J H Clark ldquoLibrary of FT-Raman spectraof pigments minerals pigment media and varnishes andsupplement to existing library of Raman spectra of pigmentswith visible excitationrdquo Spectrochimica Acta Part A Molecularand Biomolecular Spectroscopy vol 57 no 7 pp 1491ndash1521 2001
[4] F A Cotton Chemical Applications of Group Theory Wiley-Interscience Richardson Tex USA 3rd edition 1990
[5] S Gunasekaran G Anbalagan and S Pandi ldquoRaman andinfrared spectra of carbonates of calcite structurerdquo Journal ofRaman Spectroscopy vol 37 no 9 pp 892ndash899 2006
[6] N Koura S Kohara K Takeuchi et al ldquoAlkali carbonatesRaman spectroscopy ab initio calculations and structurerdquoJournal of Molecular Structure vol 382 no 3 pp 163ndash169 1996
[7] E Mattei G de Vivo A de Santis C Gaetani C Pelosiand U Santamaria ldquoRaman spectroscopic analysis of azuriteblackeningrdquo Journal of Raman Spectroscopy vol 39 no 2 pp302ndash306 2008
[8] E B Scheetz and B W White ldquoVibrational spectra of thealkaline earth double carbonatesrdquo American Mineralogist vol62 pp 36ndash50 1977
[9] J E Parker S P Thompson A R Lennie J Potter andC C Tang ldquoA study of the aragonite-calcite transformationusingRaman spectroscopy synchrotron powder diffraction andscanning electron microscopyrdquo CrystEngComm vol 12 no 5pp 1590ndash1599 2010
[10] D Krishnamurti ldquoThe Raman spectra of aragonite strontianiteand witheriterdquo Proceedings of the Indian Academy of Sciences Avol 51 no 6 pp 285ndash295 1960
[11] J Urmos S K Sharma and F T Mackenzie ldquoCharacterizationof some biogenic carbonates with Raman spectroscopyrdquo Amer-ican Mineralogist vol 76 no 3-4 pp 641ndash646 1991
[12] M Charles R Jeanloz and R J Hemley ldquoSpectroscopic andx-ray diffraction studies of metastable crystalline-amorphoustransitions in Ca(OH)
2
and serpentinerdquo Geophysical Mono-graph Series vol 67 pp 485ndash492 1992
[13] R W Gauldie S K Sharma and E Volk ldquoMicro-Ramanspectral study of vaterite and aragonite otoliths of the cohosalmon Oncorhynchus kisutchrdquo Comparative Biochemistry andPhysiology A vol 118 no 3 pp 753ndash757 1997
[14] R L Frost W N Martens L Rintoul E Mahmutagic andJ T Kloprogge ldquoRaman spectroscopic study of azurite andmalachite at 298 and 77 Krdquo Journal of Raman Spectroscopy vol33 no 4 pp 252ndash259 2002
[15] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons New York NY USA1997
[16] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons Hoboken NJ USA6th edition 2009
[17] G D Smith and R J H Clark ldquoRaman microscopy inarchaeological sciencerdquo Journal of Archaeological Science vol 31no 8 pp 1137ndash1160 2004
[18] D Bersani and J M Madariaga ldquoApplications of Raman spec-troscopy in art and archaeologyrdquo Journal of Raman Spectroscopyvol 43 no 11 pp 1523ndash1528 2012
[19] L Stagi J A De Toro A Ardu et al ldquoSurface effects undervisible irradiation and heat treatment on the phase stability of120574-Fe2
O3
nanoparticles and 120574-Fe2
O3
-SiO2
core-shell nanostruc-turesrdquo The Journal of Physical Chemistry C vol 118 no 5 pp2857ndash2866 2014
[20] D Hradil T Grygar J Hradilova and P Bezdicka ldquoClay andiron oxide pigments in the history of paintingrdquo Applied ClayScience vol 22 no 5 pp 223ndash236 2003
[21] I Aliatis D Bersani E Campani et al ldquoPigments used inRoman wall paintings in the Vesuvian areardquo Journal of RamanSpectroscopy vol 41 no 11 pp 1537ndash1542 2010
[22] H GM Edwards DW Farwell D L A de Faria et al ldquoRamanspectroscopic study of 3000minusyearminusold human skeletal remainsfrom a sambaqui Santa Catarina Brazilrdquo Journal of RamanSpectroscopy vol 32 no 1 pp 17ndash22 2001
[23] T Y Kwon T Fujishima and Y Imai ldquoFT-Raman spectroscopyof calcium hydroxide medicament in root canalsrdquo InternationalEndodontic Journal vol 37 no 7 pp 489ndash493 2004
[24] R L Frost ldquoFourier transform Raman spectroscopy of kaolin-ite dickite and halloysiterdquo Clays amp Clay Minerals vol 43 no 2pp 191ndash195 1995
[25] I C Freestone ldquoApplications and potential of electron probemicro analysis in technological and provenance investigationsof ancient ceramicsrdquo Archaeometry vol 24 no 2 pp 99ndash1161982
[26] P C Ricci C M Carbonaro L Stagi et al ldquoAnatase-to-rutilephase transition in TiO
2
nanoparticles irradiated by visiblelightrdquo Journal of Physical Chemistry C vol 117 no 15 pp 7850ndash7857 2013
[27] P C Ricci A Casu M Salis R Corpino and A AneddaldquoOptically controlled phase variation of TiO
2
nanoparticlesrdquoJournal of Physical Chemistry C vol 114 no 34 pp 14441ndash144452010
[28] S Sanchez-Moral L Luque J-C Canaveras V Soler J Garcia-Guinea and A Aparicio ldquoLime-pozzolana mortars in Romancatacombs composition structures and restorationrdquo Cementand Concrete Research vol 35 no 8 pp 1555ndash1565 2005
[29] H G M Edwards and D W Farwell ldquoThe conservationalheritage of wall paintings and buildings an FT-Raman spectro-scopic study of prehistoric Roman mediaeval and Renaissance
10 Journal of Spectroscopy
lime substrates and mortarsrdquo Journal of Raman Spectroscopyvol 39 no 8 pp 985ndash992 2008
[30] C M Sinopoli Approaches to Archaeological CeramicsSpringer Boston Mass USA 1991
[31] R Newcomb Jr Ceramic WhitewaresmdashHistory Technology andApplications Pitman Publishing New York NY USA 1947
[32] W J J Huijgen and R N J Comans ldquoCarbon dioxide seques-tration by mineral carbonation literature reviewrdquo ECN ReportECN-C-03-016 ECN 2003
[33] W Gu D W Bousfield and C P Tripp ldquoFormation of calciumcarbonate particles by direct contact of Ca(OH)
[34] N Buzgar and A I Apopei ldquoThe Raman study of certaincarbonatesrdquo Geologie vol 15 pp 97ndash112 2009
[35] S Ekbundit K Leinenweber J L Yarger J S Robinson MVerhelst-Voorhees and G H Wolf ldquoNew high-pressure phaseand pressure-induced amorphization of Ca(OH)
2
grain sizeeffectrdquo Journal of Solid State Chemistry vol 126 no 2 pp 300ndash307 1996
Figure 9 Raman spectrum of calcium hydroxide obtained heating at 1000∘C CaCO3
powders
takes place and in the spectrum shown in Figure 9(b) it ispossible to observe the presence of different bands associatedto the carbon dioxide sequestration The band at 913 cmminus1disappears (the band was present in the spectrum taken atthe beginning of the process Figure 9(a)) while it is possibleto observe the presence of the band at 863 cmminus1 which couldbe associated to the mode ]
2
of the carbonate ions weaklybonded to the cations In addition a new band at 740 cmminus1can be observed and assigned to the ]
3
symmetric CO3
2minus
bendingmode inVaterite suggesting favorable conditions forthis metastable form (120583-CaCO
3
) [13]By wetting the same calcium hydroxide powders used in
the previous experiment the ldquolimewashrdquo was realized with thepurpose to reproduce the ancient technique probably used inPompeii The limewash was mixed with hematite and used tocover the surface of two samples of clay indicated as A andB differentiated by the presence of calcite into the mixture(sample A) and no presence of calcite (samples B) into
8 Journal of Spectroscopy
(A) (B)
Figure 10 Laboratory samples sample A calcite in the mixture ofthe clay sample B absence of calcite in the clay Both the sampleswere covered with Fe
Figure 11 Raman spectrumwith deconvolutions of samples (a) and(b)
the mixture (Figure 10) Each sample was treated at 1000∘Cwith the same temperature treatment used in the previouscalcite sample As shown in Figure 10 the samples B present adifferent color in the limewash covered surface
Figure 11 reports the Raman spectra of the samples A andB with the relative deconvolutions with lorentzian profiles Itis possible to observe the presence of the bands assigned tocalcium hydroxide as indicated previously the presence ofthe band around 860 cmminus1 due to CO
3
2minus weakly bonded tothe cations and the presence of the band at 705 cmminus1 typicalfor the ]
4
frequency mode of carbonate in Aragonite phase[9]
Figure 12 reports the Raman spectrum of the sampleA collected in a cross section of the sample not exposedto the atmosphere at high temperature In this case the
Raman shift (cmminus1)
Inte
nsity
(au
)
18002000 1600 1400 1200 1000 800 600 400 200
Correlation factor (R) = 0993
Figure 12 Raman spectrum of the cross section of sample A
calcite present into the clay mixture has been transformedin calcium oxidehydroxide due to the high temperature andthe residual humidity of the clay From the analysis of theRaman spectrum it is possible to observe the phenomenonof carbonation as indicated by the absence of the band at705 cmminus1 (Aragonite phase) and a slow contribution of theband at 860 cmminus1 is shown (associated to the presence ofcarbonate ions weakly bonded to the cations) [9]
These results seems to indicate an high degree of knowl-edge of the cooking process of the pottery in the Romanage and in particular the use of calcium hydroxide as a toolto reduce the content of CO
2
in the furnace atmosphereand then obtain a more oxidant ambient and reach highertemperature close to the at the pottery surfaces
5 Conclusions
In this study a characterization of different type of potterysamples and painted fragments of wall belonging to Pompeiihas been performed by means of EDS microanalysis andRaman spectroscopy The principal results obtained concernthe use of calcium hydroxide above the surface of analyzedsamples before cooking the clay This technique of surfacetreatment seems to be not justified only for the use of avitrification additive or sealant but through this study it ispossible to suggest that calcium hydroxide could be used asldquogetterrdquo of CO
2
during the heat treatment The result of thisoperation is to reduce the content of CO
2
in the furnaceatmosphere and then obtain a more oxidant ambient whencooking the pottery In these conditions as illustrated in thisstudy the metallic oxides used as pigments on the surfaceor contained in the clay mixture could be preserved in thehigher state of oxidation providing a better esthetical result(in terms of color)
In any case these findings give new light on the potterymanufacturing techniques of Romans and in particular opennew questions about the real degree of knowledge of the
Journal of Spectroscopy 9
Romans about the art of ceramics and more general aboutchemistry and technologies
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This study has been supported by the Italian Ministryof University and Scientific Research (MIUR) within thenational grant ldquoFuturo in Ricercardquo 2012 TIME THROUGHCOLOURS Analysis of painted artifacts in their archaeolog-ical historical and sociological contexts (RBFR12405A 002)
References
[1] S P Koob ldquoThe use of Paraloid B-72 as an adhesive itsapplication for archaeological ceramics and other materialsrdquoStudies in Conservation vol 31 no 1 pp 7ndash14 1986
[2] S Chapman and D Mason ldquoLiterature review the use ofParaloid B-72 as a surface consolidant for stained glassrdquo JournalofTheAmerican Institute for Conservation vol 42 no 2 pp 381ndash392 2003
[3] L Burgio and R J H Clark ldquoLibrary of FT-Raman spectraof pigments minerals pigment media and varnishes andsupplement to existing library of Raman spectra of pigmentswith visible excitationrdquo Spectrochimica Acta Part A Molecularand Biomolecular Spectroscopy vol 57 no 7 pp 1491ndash1521 2001
[4] F A Cotton Chemical Applications of Group Theory Wiley-Interscience Richardson Tex USA 3rd edition 1990
[5] S Gunasekaran G Anbalagan and S Pandi ldquoRaman andinfrared spectra of carbonates of calcite structurerdquo Journal ofRaman Spectroscopy vol 37 no 9 pp 892ndash899 2006
[6] N Koura S Kohara K Takeuchi et al ldquoAlkali carbonatesRaman spectroscopy ab initio calculations and structurerdquoJournal of Molecular Structure vol 382 no 3 pp 163ndash169 1996
[7] E Mattei G de Vivo A de Santis C Gaetani C Pelosiand U Santamaria ldquoRaman spectroscopic analysis of azuriteblackeningrdquo Journal of Raman Spectroscopy vol 39 no 2 pp302ndash306 2008
[8] E B Scheetz and B W White ldquoVibrational spectra of thealkaline earth double carbonatesrdquo American Mineralogist vol62 pp 36ndash50 1977
[9] J E Parker S P Thompson A R Lennie J Potter andC C Tang ldquoA study of the aragonite-calcite transformationusingRaman spectroscopy synchrotron powder diffraction andscanning electron microscopyrdquo CrystEngComm vol 12 no 5pp 1590ndash1599 2010
[10] D Krishnamurti ldquoThe Raman spectra of aragonite strontianiteand witheriterdquo Proceedings of the Indian Academy of Sciences Avol 51 no 6 pp 285ndash295 1960
[11] J Urmos S K Sharma and F T Mackenzie ldquoCharacterizationof some biogenic carbonates with Raman spectroscopyrdquo Amer-ican Mineralogist vol 76 no 3-4 pp 641ndash646 1991
[12] M Charles R Jeanloz and R J Hemley ldquoSpectroscopic andx-ray diffraction studies of metastable crystalline-amorphoustransitions in Ca(OH)
2
and serpentinerdquo Geophysical Mono-graph Series vol 67 pp 485ndash492 1992
[13] R W Gauldie S K Sharma and E Volk ldquoMicro-Ramanspectral study of vaterite and aragonite otoliths of the cohosalmon Oncorhynchus kisutchrdquo Comparative Biochemistry andPhysiology A vol 118 no 3 pp 753ndash757 1997
[14] R L Frost W N Martens L Rintoul E Mahmutagic andJ T Kloprogge ldquoRaman spectroscopic study of azurite andmalachite at 298 and 77 Krdquo Journal of Raman Spectroscopy vol33 no 4 pp 252ndash259 2002
[15] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons New York NY USA1997
[16] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons Hoboken NJ USA6th edition 2009
[17] G D Smith and R J H Clark ldquoRaman microscopy inarchaeological sciencerdquo Journal of Archaeological Science vol 31no 8 pp 1137ndash1160 2004
[18] D Bersani and J M Madariaga ldquoApplications of Raman spec-troscopy in art and archaeologyrdquo Journal of Raman Spectroscopyvol 43 no 11 pp 1523ndash1528 2012
[19] L Stagi J A De Toro A Ardu et al ldquoSurface effects undervisible irradiation and heat treatment on the phase stability of120574-Fe2
O3
nanoparticles and 120574-Fe2
O3
-SiO2
core-shell nanostruc-turesrdquo The Journal of Physical Chemistry C vol 118 no 5 pp2857ndash2866 2014
[20] D Hradil T Grygar J Hradilova and P Bezdicka ldquoClay andiron oxide pigments in the history of paintingrdquo Applied ClayScience vol 22 no 5 pp 223ndash236 2003
[21] I Aliatis D Bersani E Campani et al ldquoPigments used inRoman wall paintings in the Vesuvian areardquo Journal of RamanSpectroscopy vol 41 no 11 pp 1537ndash1542 2010
[22] H GM Edwards DW Farwell D L A de Faria et al ldquoRamanspectroscopic study of 3000minusyearminusold human skeletal remainsfrom a sambaqui Santa Catarina Brazilrdquo Journal of RamanSpectroscopy vol 32 no 1 pp 17ndash22 2001
[23] T Y Kwon T Fujishima and Y Imai ldquoFT-Raman spectroscopyof calcium hydroxide medicament in root canalsrdquo InternationalEndodontic Journal vol 37 no 7 pp 489ndash493 2004
[24] R L Frost ldquoFourier transform Raman spectroscopy of kaolin-ite dickite and halloysiterdquo Clays amp Clay Minerals vol 43 no 2pp 191ndash195 1995
[25] I C Freestone ldquoApplications and potential of electron probemicro analysis in technological and provenance investigationsof ancient ceramicsrdquo Archaeometry vol 24 no 2 pp 99ndash1161982
[26] P C Ricci C M Carbonaro L Stagi et al ldquoAnatase-to-rutilephase transition in TiO
2
nanoparticles irradiated by visiblelightrdquo Journal of Physical Chemistry C vol 117 no 15 pp 7850ndash7857 2013
[27] P C Ricci A Casu M Salis R Corpino and A AneddaldquoOptically controlled phase variation of TiO
2
nanoparticlesrdquoJournal of Physical Chemistry C vol 114 no 34 pp 14441ndash144452010
[28] S Sanchez-Moral L Luque J-C Canaveras V Soler J Garcia-Guinea and A Aparicio ldquoLime-pozzolana mortars in Romancatacombs composition structures and restorationrdquo Cementand Concrete Research vol 35 no 8 pp 1555ndash1565 2005
[29] H G M Edwards and D W Farwell ldquoThe conservationalheritage of wall paintings and buildings an FT-Raman spectro-scopic study of prehistoric Roman mediaeval and Renaissance
10 Journal of Spectroscopy
lime substrates and mortarsrdquo Journal of Raman Spectroscopyvol 39 no 8 pp 985ndash992 2008
[30] C M Sinopoli Approaches to Archaeological CeramicsSpringer Boston Mass USA 1991
[31] R Newcomb Jr Ceramic WhitewaresmdashHistory Technology andApplications Pitman Publishing New York NY USA 1947
[32] W J J Huijgen and R N J Comans ldquoCarbon dioxide seques-tration by mineral carbonation literature reviewrdquo ECN ReportECN-C-03-016 ECN 2003
[33] W Gu D W Bousfield and C P Tripp ldquoFormation of calciumcarbonate particles by direct contact of Ca(OH)
[34] N Buzgar and A I Apopei ldquoThe Raman study of certaincarbonatesrdquo Geologie vol 15 pp 97ndash112 2009
[35] S Ekbundit K Leinenweber J L Yarger J S Robinson MVerhelst-Voorhees and G H Wolf ldquoNew high-pressure phaseand pressure-induced amorphization of Ca(OH)
2
grain sizeeffectrdquo Journal of Solid State Chemistry vol 126 no 2 pp 300ndash307 1996
Figure 11 Raman spectrumwith deconvolutions of samples (a) and(b)
the mixture (Figure 10) Each sample was treated at 1000∘Cwith the same temperature treatment used in the previouscalcite sample As shown in Figure 10 the samples B present adifferent color in the limewash covered surface
Figure 11 reports the Raman spectra of the samples A andB with the relative deconvolutions with lorentzian profiles Itis possible to observe the presence of the bands assigned tocalcium hydroxide as indicated previously the presence ofthe band around 860 cmminus1 due to CO
3
2minus weakly bonded tothe cations and the presence of the band at 705 cmminus1 typicalfor the ]
4
frequency mode of carbonate in Aragonite phase[9]
Figure 12 reports the Raman spectrum of the sampleA collected in a cross section of the sample not exposedto the atmosphere at high temperature In this case the
Raman shift (cmminus1)
Inte
nsity
(au
)
18002000 1600 1400 1200 1000 800 600 400 200
Correlation factor (R) = 0993
Figure 12 Raman spectrum of the cross section of sample A
calcite present into the clay mixture has been transformedin calcium oxidehydroxide due to the high temperature andthe residual humidity of the clay From the analysis of theRaman spectrum it is possible to observe the phenomenonof carbonation as indicated by the absence of the band at705 cmminus1 (Aragonite phase) and a slow contribution of theband at 860 cmminus1 is shown (associated to the presence ofcarbonate ions weakly bonded to the cations) [9]
These results seems to indicate an high degree of knowl-edge of the cooking process of the pottery in the Romanage and in particular the use of calcium hydroxide as a toolto reduce the content of CO
2
in the furnace atmosphereand then obtain a more oxidant ambient and reach highertemperature close to the at the pottery surfaces
5 Conclusions
In this study a characterization of different type of potterysamples and painted fragments of wall belonging to Pompeiihas been performed by means of EDS microanalysis andRaman spectroscopy The principal results obtained concernthe use of calcium hydroxide above the surface of analyzedsamples before cooking the clay This technique of surfacetreatment seems to be not justified only for the use of avitrification additive or sealant but through this study it ispossible to suggest that calcium hydroxide could be used asldquogetterrdquo of CO
2
during the heat treatment The result of thisoperation is to reduce the content of CO
2
in the furnaceatmosphere and then obtain a more oxidant ambient whencooking the pottery In these conditions as illustrated in thisstudy the metallic oxides used as pigments on the surfaceor contained in the clay mixture could be preserved in thehigher state of oxidation providing a better esthetical result(in terms of color)
In any case these findings give new light on the potterymanufacturing techniques of Romans and in particular opennew questions about the real degree of knowledge of the
Journal of Spectroscopy 9
Romans about the art of ceramics and more general aboutchemistry and technologies
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This study has been supported by the Italian Ministryof University and Scientific Research (MIUR) within thenational grant ldquoFuturo in Ricercardquo 2012 TIME THROUGHCOLOURS Analysis of painted artifacts in their archaeolog-ical historical and sociological contexts (RBFR12405A 002)
References
[1] S P Koob ldquoThe use of Paraloid B-72 as an adhesive itsapplication for archaeological ceramics and other materialsrdquoStudies in Conservation vol 31 no 1 pp 7ndash14 1986
[2] S Chapman and D Mason ldquoLiterature review the use ofParaloid B-72 as a surface consolidant for stained glassrdquo JournalofTheAmerican Institute for Conservation vol 42 no 2 pp 381ndash392 2003
[3] L Burgio and R J H Clark ldquoLibrary of FT-Raman spectraof pigments minerals pigment media and varnishes andsupplement to existing library of Raman spectra of pigmentswith visible excitationrdquo Spectrochimica Acta Part A Molecularand Biomolecular Spectroscopy vol 57 no 7 pp 1491ndash1521 2001
[4] F A Cotton Chemical Applications of Group Theory Wiley-Interscience Richardson Tex USA 3rd edition 1990
[5] S Gunasekaran G Anbalagan and S Pandi ldquoRaman andinfrared spectra of carbonates of calcite structurerdquo Journal ofRaman Spectroscopy vol 37 no 9 pp 892ndash899 2006
[6] N Koura S Kohara K Takeuchi et al ldquoAlkali carbonatesRaman spectroscopy ab initio calculations and structurerdquoJournal of Molecular Structure vol 382 no 3 pp 163ndash169 1996
[7] E Mattei G de Vivo A de Santis C Gaetani C Pelosiand U Santamaria ldquoRaman spectroscopic analysis of azuriteblackeningrdquo Journal of Raman Spectroscopy vol 39 no 2 pp302ndash306 2008
[8] E B Scheetz and B W White ldquoVibrational spectra of thealkaline earth double carbonatesrdquo American Mineralogist vol62 pp 36ndash50 1977
[9] J E Parker S P Thompson A R Lennie J Potter andC C Tang ldquoA study of the aragonite-calcite transformationusingRaman spectroscopy synchrotron powder diffraction andscanning electron microscopyrdquo CrystEngComm vol 12 no 5pp 1590ndash1599 2010
[10] D Krishnamurti ldquoThe Raman spectra of aragonite strontianiteand witheriterdquo Proceedings of the Indian Academy of Sciences Avol 51 no 6 pp 285ndash295 1960
[11] J Urmos S K Sharma and F T Mackenzie ldquoCharacterizationof some biogenic carbonates with Raman spectroscopyrdquo Amer-ican Mineralogist vol 76 no 3-4 pp 641ndash646 1991
[12] M Charles R Jeanloz and R J Hemley ldquoSpectroscopic andx-ray diffraction studies of metastable crystalline-amorphoustransitions in Ca(OH)
2
and serpentinerdquo Geophysical Mono-graph Series vol 67 pp 485ndash492 1992
[13] R W Gauldie S K Sharma and E Volk ldquoMicro-Ramanspectral study of vaterite and aragonite otoliths of the cohosalmon Oncorhynchus kisutchrdquo Comparative Biochemistry andPhysiology A vol 118 no 3 pp 753ndash757 1997
[14] R L Frost W N Martens L Rintoul E Mahmutagic andJ T Kloprogge ldquoRaman spectroscopic study of azurite andmalachite at 298 and 77 Krdquo Journal of Raman Spectroscopy vol33 no 4 pp 252ndash259 2002
[15] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons New York NY USA1997
[16] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons Hoboken NJ USA6th edition 2009
[17] G D Smith and R J H Clark ldquoRaman microscopy inarchaeological sciencerdquo Journal of Archaeological Science vol 31no 8 pp 1137ndash1160 2004
[18] D Bersani and J M Madariaga ldquoApplications of Raman spec-troscopy in art and archaeologyrdquo Journal of Raman Spectroscopyvol 43 no 11 pp 1523ndash1528 2012
[19] L Stagi J A De Toro A Ardu et al ldquoSurface effects undervisible irradiation and heat treatment on the phase stability of120574-Fe2
O3
nanoparticles and 120574-Fe2
O3
-SiO2
core-shell nanostruc-turesrdquo The Journal of Physical Chemistry C vol 118 no 5 pp2857ndash2866 2014
[20] D Hradil T Grygar J Hradilova and P Bezdicka ldquoClay andiron oxide pigments in the history of paintingrdquo Applied ClayScience vol 22 no 5 pp 223ndash236 2003
[21] I Aliatis D Bersani E Campani et al ldquoPigments used inRoman wall paintings in the Vesuvian areardquo Journal of RamanSpectroscopy vol 41 no 11 pp 1537ndash1542 2010
[22] H GM Edwards DW Farwell D L A de Faria et al ldquoRamanspectroscopic study of 3000minusyearminusold human skeletal remainsfrom a sambaqui Santa Catarina Brazilrdquo Journal of RamanSpectroscopy vol 32 no 1 pp 17ndash22 2001
[23] T Y Kwon T Fujishima and Y Imai ldquoFT-Raman spectroscopyof calcium hydroxide medicament in root canalsrdquo InternationalEndodontic Journal vol 37 no 7 pp 489ndash493 2004
[24] R L Frost ldquoFourier transform Raman spectroscopy of kaolin-ite dickite and halloysiterdquo Clays amp Clay Minerals vol 43 no 2pp 191ndash195 1995
[25] I C Freestone ldquoApplications and potential of electron probemicro analysis in technological and provenance investigationsof ancient ceramicsrdquo Archaeometry vol 24 no 2 pp 99ndash1161982
[26] P C Ricci C M Carbonaro L Stagi et al ldquoAnatase-to-rutilephase transition in TiO
2
nanoparticles irradiated by visiblelightrdquo Journal of Physical Chemistry C vol 117 no 15 pp 7850ndash7857 2013
[27] P C Ricci A Casu M Salis R Corpino and A AneddaldquoOptically controlled phase variation of TiO
2
nanoparticlesrdquoJournal of Physical Chemistry C vol 114 no 34 pp 14441ndash144452010
[28] S Sanchez-Moral L Luque J-C Canaveras V Soler J Garcia-Guinea and A Aparicio ldquoLime-pozzolana mortars in Romancatacombs composition structures and restorationrdquo Cementand Concrete Research vol 35 no 8 pp 1555ndash1565 2005
[29] H G M Edwards and D W Farwell ldquoThe conservationalheritage of wall paintings and buildings an FT-Raman spectro-scopic study of prehistoric Roman mediaeval and Renaissance
10 Journal of Spectroscopy
lime substrates and mortarsrdquo Journal of Raman Spectroscopyvol 39 no 8 pp 985ndash992 2008
[30] C M Sinopoli Approaches to Archaeological CeramicsSpringer Boston Mass USA 1991
[31] R Newcomb Jr Ceramic WhitewaresmdashHistory Technology andApplications Pitman Publishing New York NY USA 1947
[32] W J J Huijgen and R N J Comans ldquoCarbon dioxide seques-tration by mineral carbonation literature reviewrdquo ECN ReportECN-C-03-016 ECN 2003
[33] W Gu D W Bousfield and C P Tripp ldquoFormation of calciumcarbonate particles by direct contact of Ca(OH)
[34] N Buzgar and A I Apopei ldquoThe Raman study of certaincarbonatesrdquo Geologie vol 15 pp 97ndash112 2009
[35] S Ekbundit K Leinenweber J L Yarger J S Robinson MVerhelst-Voorhees and G H Wolf ldquoNew high-pressure phaseand pressure-induced amorphization of Ca(OH)
2
grain sizeeffectrdquo Journal of Solid State Chemistry vol 126 no 2 pp 300ndash307 1996
Romans about the art of ceramics and more general aboutchemistry and technologies
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This study has been supported by the Italian Ministryof University and Scientific Research (MIUR) within thenational grant ldquoFuturo in Ricercardquo 2012 TIME THROUGHCOLOURS Analysis of painted artifacts in their archaeolog-ical historical and sociological contexts (RBFR12405A 002)
References
[1] S P Koob ldquoThe use of Paraloid B-72 as an adhesive itsapplication for archaeological ceramics and other materialsrdquoStudies in Conservation vol 31 no 1 pp 7ndash14 1986
[2] S Chapman and D Mason ldquoLiterature review the use ofParaloid B-72 as a surface consolidant for stained glassrdquo JournalofTheAmerican Institute for Conservation vol 42 no 2 pp 381ndash392 2003
[3] L Burgio and R J H Clark ldquoLibrary of FT-Raman spectraof pigments minerals pigment media and varnishes andsupplement to existing library of Raman spectra of pigmentswith visible excitationrdquo Spectrochimica Acta Part A Molecularand Biomolecular Spectroscopy vol 57 no 7 pp 1491ndash1521 2001
[4] F A Cotton Chemical Applications of Group Theory Wiley-Interscience Richardson Tex USA 3rd edition 1990
[5] S Gunasekaran G Anbalagan and S Pandi ldquoRaman andinfrared spectra of carbonates of calcite structurerdquo Journal ofRaman Spectroscopy vol 37 no 9 pp 892ndash899 2006
[6] N Koura S Kohara K Takeuchi et al ldquoAlkali carbonatesRaman spectroscopy ab initio calculations and structurerdquoJournal of Molecular Structure vol 382 no 3 pp 163ndash169 1996
[7] E Mattei G de Vivo A de Santis C Gaetani C Pelosiand U Santamaria ldquoRaman spectroscopic analysis of azuriteblackeningrdquo Journal of Raman Spectroscopy vol 39 no 2 pp302ndash306 2008
[8] E B Scheetz and B W White ldquoVibrational spectra of thealkaline earth double carbonatesrdquo American Mineralogist vol62 pp 36ndash50 1977
[9] J E Parker S P Thompson A R Lennie J Potter andC C Tang ldquoA study of the aragonite-calcite transformationusingRaman spectroscopy synchrotron powder diffraction andscanning electron microscopyrdquo CrystEngComm vol 12 no 5pp 1590ndash1599 2010
[10] D Krishnamurti ldquoThe Raman spectra of aragonite strontianiteand witheriterdquo Proceedings of the Indian Academy of Sciences Avol 51 no 6 pp 285ndash295 1960
[11] J Urmos S K Sharma and F T Mackenzie ldquoCharacterizationof some biogenic carbonates with Raman spectroscopyrdquo Amer-ican Mineralogist vol 76 no 3-4 pp 641ndash646 1991
[12] M Charles R Jeanloz and R J Hemley ldquoSpectroscopic andx-ray diffraction studies of metastable crystalline-amorphoustransitions in Ca(OH)
2
and serpentinerdquo Geophysical Mono-graph Series vol 67 pp 485ndash492 1992
[13] R W Gauldie S K Sharma and E Volk ldquoMicro-Ramanspectral study of vaterite and aragonite otoliths of the cohosalmon Oncorhynchus kisutchrdquo Comparative Biochemistry andPhysiology A vol 118 no 3 pp 753ndash757 1997
[14] R L Frost W N Martens L Rintoul E Mahmutagic andJ T Kloprogge ldquoRaman spectroscopic study of azurite andmalachite at 298 and 77 Krdquo Journal of Raman Spectroscopy vol33 no 4 pp 252ndash259 2002
[15] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons New York NY USA1997
[16] K Nakamoto Infrared and Raman Spectra of Inorganic andCoordination Compounds Part A Theory and Applications inInorganic Chemistry John Wiley amp Sons Hoboken NJ USA6th edition 2009
[17] G D Smith and R J H Clark ldquoRaman microscopy inarchaeological sciencerdquo Journal of Archaeological Science vol 31no 8 pp 1137ndash1160 2004
[18] D Bersani and J M Madariaga ldquoApplications of Raman spec-troscopy in art and archaeologyrdquo Journal of Raman Spectroscopyvol 43 no 11 pp 1523ndash1528 2012
[19] L Stagi J A De Toro A Ardu et al ldquoSurface effects undervisible irradiation and heat treatment on the phase stability of120574-Fe2
O3
nanoparticles and 120574-Fe2
O3
-SiO2
core-shell nanostruc-turesrdquo The Journal of Physical Chemistry C vol 118 no 5 pp2857ndash2866 2014
[20] D Hradil T Grygar J Hradilova and P Bezdicka ldquoClay andiron oxide pigments in the history of paintingrdquo Applied ClayScience vol 22 no 5 pp 223ndash236 2003
[21] I Aliatis D Bersani E Campani et al ldquoPigments used inRoman wall paintings in the Vesuvian areardquo Journal of RamanSpectroscopy vol 41 no 11 pp 1537ndash1542 2010
[22] H GM Edwards DW Farwell D L A de Faria et al ldquoRamanspectroscopic study of 3000minusyearminusold human skeletal remainsfrom a sambaqui Santa Catarina Brazilrdquo Journal of RamanSpectroscopy vol 32 no 1 pp 17ndash22 2001
[23] T Y Kwon T Fujishima and Y Imai ldquoFT-Raman spectroscopyof calcium hydroxide medicament in root canalsrdquo InternationalEndodontic Journal vol 37 no 7 pp 489ndash493 2004
[24] R L Frost ldquoFourier transform Raman spectroscopy of kaolin-ite dickite and halloysiterdquo Clays amp Clay Minerals vol 43 no 2pp 191ndash195 1995
[25] I C Freestone ldquoApplications and potential of electron probemicro analysis in technological and provenance investigationsof ancient ceramicsrdquo Archaeometry vol 24 no 2 pp 99ndash1161982
[26] P C Ricci C M Carbonaro L Stagi et al ldquoAnatase-to-rutilephase transition in TiO
2
nanoparticles irradiated by visiblelightrdquo Journal of Physical Chemistry C vol 117 no 15 pp 7850ndash7857 2013
[27] P C Ricci A Casu M Salis R Corpino and A AneddaldquoOptically controlled phase variation of TiO
2
nanoparticlesrdquoJournal of Physical Chemistry C vol 114 no 34 pp 14441ndash144452010
[28] S Sanchez-Moral L Luque J-C Canaveras V Soler J Garcia-Guinea and A Aparicio ldquoLime-pozzolana mortars in Romancatacombs composition structures and restorationrdquo Cementand Concrete Research vol 35 no 8 pp 1555ndash1565 2005
[29] H G M Edwards and D W Farwell ldquoThe conservationalheritage of wall paintings and buildings an FT-Raman spectro-scopic study of prehistoric Roman mediaeval and Renaissance
10 Journal of Spectroscopy
lime substrates and mortarsrdquo Journal of Raman Spectroscopyvol 39 no 8 pp 985ndash992 2008
[30] C M Sinopoli Approaches to Archaeological CeramicsSpringer Boston Mass USA 1991
[31] R Newcomb Jr Ceramic WhitewaresmdashHistory Technology andApplications Pitman Publishing New York NY USA 1947
[32] W J J Huijgen and R N J Comans ldquoCarbon dioxide seques-tration by mineral carbonation literature reviewrdquo ECN ReportECN-C-03-016 ECN 2003
[33] W Gu D W Bousfield and C P Tripp ldquoFormation of calciumcarbonate particles by direct contact of Ca(OH)
[34] N Buzgar and A I Apopei ldquoThe Raman study of certaincarbonatesrdquo Geologie vol 15 pp 97ndash112 2009
[35] S Ekbundit K Leinenweber J L Yarger J S Robinson MVerhelst-Voorhees and G H Wolf ldquoNew high-pressure phaseand pressure-induced amorphization of Ca(OH)
2
grain sizeeffectrdquo Journal of Solid State Chemistry vol 126 no 2 pp 300ndash307 1996
[34] N Buzgar and A I Apopei ldquoThe Raman study of certaincarbonatesrdquo Geologie vol 15 pp 97ndash112 2009
[35] S Ekbundit K Leinenweber J L Yarger J S Robinson MVerhelst-Voorhees and G H Wolf ldquoNew high-pressure phaseand pressure-induced amorphization of Ca(OH)
2
grain sizeeffectrdquo Journal of Solid State Chemistry vol 126 no 2 pp 300ndash307 1996
