Faculty of Electrical Engineering and Information Technology, Slovak University of Technology, Ilkovicova 3, 812 19 Bratislava, SlovakiaFaculty of Materials Science and Technology, Slovak University of Technology, Paulínska 16, 917 24 Trnava, SlovakiaFaculty of Natural Sciences, Comenius University, Mlynská dolina, 842 15 Bratislava, Slovakia
r t i c l e i n f o
rticle history:eceived 4 April 2012eceived in revised form 18 October 2012ccepted 18 October 2012vailable online 26 October 2012
eywords:
a b s t r a c t
In this paper we studied the material composition of the ground layer of a neoclassical painting. Weused Raman spectroscopy (RS) as a prime method. Thereafter scanning electron microscopy combinedwith energy dispersive spectroscopy (SEM–EDS) and X-ray powder diffraction (XRD) were employed ascomplementary techniques. The painting inspected was of the side altar in King St. Stephen’s Church inGalanta (Slovakia), signed and dated by Jos. Chr. Mayer 1870. Analysis was carried out on both covered anduncovered ground layers. Four principal compounds (barite, lead white, calcite, dolomite) and two minor
aman spectroscopyDS mapping-ray diffractionil paintingovered ground layer
compounds (sphalerite, quartz) were identified. This ground composition is consistent with the 19thcentury painting technique used in Central Europe consisting of white pigments and white fillers. Trans-formation of lead white occurred under laser irradiation. Subdominant Raman peaks of the componentswere measured. The observed results elucidate useful partnership of RS and SEM–EDS measurementssupported by X-ray powder diffraction as well as possibilities and limitations of non-destructive analysisof covered lower layers by RS.
The ongoing advance in spectroscopic instrumentation offers aange of possibilities in analysis of precious artworks. Raman spec-roscopy [1] and various other methods [2–4] have become almostbligatory analytical tools for examining the painted cultural her-tage. Even though convincing competence of such techniques haslready been proved in the field, mostly they remain a business ofcademic research or larger organizations and museums.
Non-destructive analysis of artwork is preferred though min-mal microsampling may be done when necessary. Nevertheless,
icro-sampling is needed in order to achieve entire analyticalnformation within specimen’s stratigraphy. A polished cross sec-ion is believed to be the best methodology of sampling in the fieldf art, since it uncovers multilayered structures. One can executerucial analysis on such cross sections but there still remains the
iscomfort (and limitation in number) of those locations which areermitted to be sampled within the artwork. Therefore, much effort
s dedicated to spectroscopic methods that are able to carry out the
analysis without sampling and, of course, without vacuuming [5,6].Within the span of non-destructive methods, Raman spectroscopyis considered as promising but also time-consuming due to fluores-cence problems [7]. However, the ability of Raman spectroscopy inexamining the materials covered with upper layers still remainsuncertain [8].
We have examined a painting dating to 1870 and signed by Jos.Chr. Mayer. The painting analyzed is located in King St. Stephens’Church in Galanta (Slovakia) and depicts St. Anthony from Paduain ecstasy while seeing infant Jesus. The work evidently carriesattributes of pictorial abstention typical for the 19th century. Dueto a high degree of pollution, the painting underwent restoration in2011. Prior to cleaning, the object of interest was sampled in orderto analyze the materials used and characterize overpaintings. Inthis paper we have focused on the composition of the ground layerto reinforce the knowledge base of the 19th century painting tech-nique used in the Central European region. Raman spectroscopy,SEM–EDS and X-ray powder diffraction were employed consecu-tively. Measurements were carried out on an uncovered groundlayer as well as on the painted ground.
In contrast to the 18th century’s baroque bolus grounds contain-ing ferric earthy pigments and clay minerals, the 19th century’sgrounds returned back to a more common composition made ofwhite pigments and additives. In the study we demonstrate the
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2.4. XRD
Lastly, the specimens S1 and S2a were reinspected by powder X-ray diffraction using a Bruker D-8 Advance powder diffractometer
Table 1List of samples and experimental methods used, O denotes the method utilized, Xdenotes the method was not utilized, asterisk stands for measurements on crosssections.
Sample no. Experimental method
ig. 1. Side altar painting of St. Anthony from Padua (173 cm × 348 cm) situated ining St. Stephen’s Church in Galanta, Slovakia. Sampling locations are designatedy arrows.
apability of RS for inspecting fluorescence samples and for uncov-ring weak Raman bands.
. Experimental details
SEM–EDS and XRD were used to verify and support the mea-ured Raman spectra in microscale as well as in macroscale. Fornalytic purposes, the painting was sampled at two areas givinghree samples in total. Sample 1 was covered by a paint layer,ample 2a consisted of only the ground layer without any prepa-ation or imprimatura and, finally, Sample 2b was covered withwo paint layers supported by the ground. The goal was to analyzehe ground layer without removing the paint from the specimenurface. Thanks to the variability of samples it was possible to ana-yze both the pure ground directly and the same ground coveredy different paint layers (Table 1).
.1. Sample preparation
Two areas of the painting were sampled, the points indicatinghese areas are shown in Fig. 1. In total, three samples were obtainedecause of dividing the more complex specimen of Sample 2 in twoieces. These samples were labeled as S1, S2a and S2b. Sample S1as coated dark brown-greenish, S2a was the pure ground (there-
ore it could serve as a reference for the ground layer) and S2b wasovered with a gray-greenish layer of paint. The surfaces of theamples were softly cleaned with toluene to eliminate dust andhe uppermost varnish layer contributions to the measured Ramanpectra. Thereafter, two cross sections were prepared by embed-
ing in thixotropic polyester (isophthalic) resin and mechanicallyolished using SiC sandpaper with grit size 2500 and 4000. Afterolishing, cross sections were cleaned with isopropyl alcohol andeionised water and subsequently dried in airflow. The samples
Fig. 2. Dark field photomicrograph of CS2b: (1) paint layers, (2) ground and (3)insulation.
were designated as CS2a and CS2b. Sample CS2a was a cross sec-tion from S2a, and CS2b from S2b. Fig. 2 shows a photomicrographof CS2b in dark field.
2.2. Raman spectroscopy
Samples S1, S2a and S2b were examined using a JobinYvonLabram 300 Raman confocal microscope. The apparatus includeda He–Ne laser providing 632.8 nm monochromatic light, a gridmonochromator with 1800 grooves/mm and a CCD air cooled mul-tichannel detector with resolution better than 1.3 cm–1. Duringmeasurement, the laser power was set up at either 1.7 or 17 mW.The entire measurement time was only 500 s. The spectrometerwas calibrated on the 520.7 cm–1 band of single crystalline silicon(1 0 0). The confocal hole and the slit were maintained at maximumapertures to ensure all the scattered light entering the detectionsystem. Each spectrum was recorded via an 80×, long workingdistance objective in backscattering geometry. The spectra wereprocessed by the software package Labspec and by Origin.
2.3. SEM–EDS
Electron imaging and elemental analysis were carried out onsamples CS2a and CS2b. Both cross sections were covered by athin film of evaporated carbon. The instrumentation used was athermal field emission JEOL 7600F microscope with an energy-dispersive detector. The specimens were supported by a stub usinga double-sided carbon tape to disperse the accumulated charge. Theequipment was calibrated on Mn(K�) with a resolution of 125 eV.An accelerating voltage of 20 kV was applied with a probe currentof 80 �A. The cross sections were observed under SE detector andEDS analysis was executed at selected points and areas. AdditionalEDS maps of elements of specific interest were obtained in ordereither to see the correlation between the elements or to clarify theirdistribution and abundance. EDS spectra and maps were processedwith INCA Energy 350 software.
RS SEM–EDS* XRD
S1 O X OS2a, CS2a* O O OS2b, CS2b* O O X
694 L’ . Vanco et al. / Applied Surface Science 264 (2013) 692– 698
Fig. 3. Raman spectra taken from sample S2a. The observed vibrations are denoted by their irreducible representation: v1, v2, v4 and T represent symmetric stretching,s ectivc mplex
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ymmetric bending, asymmetric bending and translation (or liberation) modes, respomponent, possibly litharge, (e) lead white and (f) deconvolution of lead white co
perating with Cu (K�) radiation (8.04 keV). An acceleratingoltage of 40 kV was applied with 40 mA current.
. Results and discussion
Since the experiment was extensive, only selected results areeported herein.
ely. (a) �-Quartz, (b) dolomite, (c) calcite + dolomite mixture, (d) baryte + unknown peak in the range 80–280 cm–1.
No Raman spectra were observed at the typical surface of sampleS1. The pigment was distributed uniformly on the ground layer andthe laser beam did not penetrate the upper layer. Only at the bordersof crackles, where the ground peeps out (or at similar defects), the
spectrum of the ground compounds could be observed.
Fig. 3 shows the Raman spectra of sample S2a. In the spec-tra, dominant bands of carbonates and sulfates and quartz areclearly visible. Namely they occur at wavenumbers 464 cm–1
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Fig. 4. (a) Raman spectrum at a typical surface of S2b. (b) Normalized doublet of S2b (green) and comparison with the same doublet taken from S2a (red). (For interpretationof the references to color in the artwork, the reader is referred to the web version of the article.)
Fig. 5. (a) Optical microscope image from S2a. The arrow indicates thermal degradation of the lead pigment under laser irradiation at the border of the beamspot. (b) ResultingRaman spectrum of massicot.
Fig. 6. (a) Secondary electron image of sample CS2a denoting four areas/points analyzed with EDS. (b) Secondary electron image of sample CS2b.
696 L’ . Vanco et al. / Applied Surface Science 264 (2013) 692– 698
Table 2Quantitative EDS analysis of CS2a, analyzed areas are highlighted in Fig. 6a.
Fig. 7. EDS maps of selected elements of specimen CS2b.
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Fig. 8. (a) Diffractogram of sample S1. (b) Diffractogram of sample S2a. Letters stand for the following: b: barite, h: hydrocerussite, d: dolomite, c: calcite.
Table 3Identified (O) and unidentified (X) compounds in the discussed samples by involved methods. Double asterisk is reserved for identification in the upper paint layer.
Component Chemical formula RS EDS XRD
S1 covered S2a pure S2b covered CS2a CS2b S1 S2a
Barite BaSO4 X O X O O O OLead white xPbCO3·yPb(OH)2 X O ** O O O ODolomitic chalk(calcite + dolomite)
CaCO3 X O X O O O OMgCa(CO3)2 X O X O O O O
Sphalerite ZnS X X X O X X XO
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�-quartz), 986 cm–1 (barite), 1048 and 1051 cm–1 (hydrocerus-ite), 1085 cm–1 (calcite) and 1096 cm–1 (dolomite). Furthermore,ubdominant peaks and also shoulders are clearly visible arisingither from symmetric and asymmetric bending vibrations or fromranslations (peak assignment is clear from Fig. 3). We suggest theresence of litharge (Fig. 3d) intentionally added as a drier for theaint binder as opposed to a pigment. The use of such additives waseported in tractates by Baldinucci, de Mayerne, de Piles and oth-rs already in the 17th century. Deconvolution of external modes ofead white extracted four peaks of hydrocerussite or cerussite lead
hite. It is reported elsewhere that they vary in the wavenumberhift. A closer approach to the composition of lead white can beade by EDS and, possibly, by XRD or synchrotron radiation [9].Only one doublet peak was recognized in the very weak spec-
rum of sample S2b, see Fig. 4(a), which was covered by an unknownray-greenish pigment with a uniform distribution on the surface.his peak is characterized by a lower signal to noise ratio. Whenormalized and compared with the same peak referred in spectrum
n Fig. 3(e), broadening of the 1052 cm–1 maximum is observed. Itay bode some change of lead white in a specific binder. In this
ase the laser beam was not able to penetrate through the upperayer of the lead pigment, although it was very thin (for stratigra-hy and elementary composition of sample S2b see Figs. 6b and 7).his was also the reason why even dominant peaks of the groundere not present in the spectrum of S2b.
Finally, in those cases, when hydrocerussite was irradiated byn intensive laser spot, degradation of the sample occurred result-ng in lead pigment transformation. Such observations have alreadyeen published but there is no general agreement on the decom-
osition products of lead white [10–13]. In Fig. 5(a) one can seehermal transformation of matter in an area exposed to strongaser irradiation, especially at the periphery. Decomposition prod-cts vary with temperature and exposure time [14], the resulting
X O O X X
spectrum in Fig. 5(b) in our study was the spectrum of massicot[15] (orthorhombic lead oxide).
Concerning the measured spectra, Raman spectroscopydetected four major compounds present in the ground layer. Theywere barite white (barium sulfate), lead white (hydrocerussiteor/and cerussite) and a mixture of dolomite and calcite (formingdolomitic chalk together).
To confirm the compounds analyzed by RS, SEM–EDS mea-surements appended by EDS mapping were added. Also theamount and distribution of elements within the specimens wasregarded. Fig. 6(a) includes CS2a in secondary electron image modeand selected areas/points analyzed. Besides lead, barium, calciumand magnesium, EDS revealed traces of zinc and sulfur mappedtogether. Zinc and sulfur can occur because of three reasons: thepresence of sphalerite, lead ore inclusions (galena), or lithopone(BaSO4 + ZnS). According to the date of development of lithopone(1870s) we did not presume such a pioneering use of the pigment.We definitely excluded the presence of lithopone forasmuch asbarium and zinc were not mapped together so as lead and sul-fur were uncorrelated. Therefore we suggest the first possibility.Sphalerite occurs in metallic veins and is usually associated withcalcite, quartz and occasionally with barite. Therefore we proposethe natural origin of relating ground compounds. In CS2a, siliconwas found correlated to oxygen, both arising from quartz. Thereare many forms of lead white and they vary in the Pb/O ratio [16].However, one cannot calculate this ratio reliably from the quanti-tative data measured by EDS [17]. Table 2 shows the EDS data fromsample CS2a achieved with internal standards included within theEDS software.
Besides elemental distribution and EDS spectra, stratigraphy ofCS2b was inspected. Two upper layers supported by the groundand mainly consisting of lead and carbon could be either two paintlayers or imprimatura with only one paint layer, Fig. 6(b). It is
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uggested that laser light used in Raman spectroscopy was notble to penetrate through the two layers and illuminate the groundayer. Therefore the Raman spectrum in Fig. 4(a) was left withoutny peaks corresponding to ground material.
Elemental maps of barium, lead, calcium and magnesium frompecimen CS2b showed their distribution and elements werepread out uniformly within the cross section (Fig. 7). Concern-ng the habits of preparing the ground layers, it was necessary toxamine the iron content in the cross section. If a ferric substanceppeared, then one could conclude that the ground was toned withome earth pigment. Such a situation would be in accord with oldainting techniques. However, only a tiny iron particle was present
n CS2b. In this case, the ground was of white color without furtheronal adjustment.
Fig. 8 shows diffractograms of samples S1 and S2a. It is clearlyeen that the peaks of particular compounds might overlay otherignificant maxima. For example the presence of quartz is uncertainnd cannot be deduced reliably. Also some other maxima overlaidach other, for instance barite and calcite and/or hydrocerussite.ome studies have proved the usefulness of micro diffraction inuch cases [18,19].
Diffractograms of both samples were almost the same, variednly in the intensities at some maxima. Neither iron nor sphaleriteontents were observed in S1 or S2a. Diagnostic peaks of baritet 0.390, 0.344 and 0.311 nm were observed in both specimens.ifferences in peak intensity at 0.272 nm could be given by thereferential orientation of barite. The same situation appeared at.262 nm in the case of hydrocerussite with diagnostic maxima at.361, 0.329 and 0.262 nm.
Calcite was specified by peaks at 0.386, 0.303 and 0.228 nm,nd dolomite at 0.403, 0.288 and 0.219 nm. Comparing the rela-ive intensities of calcite with dolomite suggests that the amountf dolomite was much lower than that of calcite.
. Conclusions
This case study encouraged the useful partnership of Ramanpectroscopy and SEM–EDS measurements. Utilization of X-rayowder diffraction along with Raman spectroscopy was found to beedundant. Perhaps this kind of cooperation would be more help-ul when some clay minerals occur in the analyzed layers. Whenhe ground layer was covered by a continuous paint layer hav-ng several tens of micrometers in depth, then the impinging laseream of 17 mW power was not able to penetrate through the paint
ayers and therefore the ground could not be examined. One canlways find an opportunity to collect Raman spectra on the bor-ers of crackles because the paint layers always bulks up creatingonvex areas in microscopic scale. Therefore Raman spectroscopy,lthough still remaining as a surface method, is able to inspect thenderlying layers. Weak subdominant modes can be visualized andven deconvoluted.
Raman spectroscopy as a prime method identified compoundsf the ground layer which were quartz, lead white, barite,phalerite, dolomitic chalk and possibly litharge traces as a desic-ant. SEM–EDS appropriately completed the analysis. Compounds
evealed by different experimental methods are summarized inable 3. In those cases, when a particular component was spreadrregularly or had a low concentration, it was detectable only byEM–EDS.
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ience 264 (2013) 692– 698
Acknowledgements
The work has been supported by the MORTEV project of the Slo-vak University of Technology in Bratislava. The authors would liketo express their gratitude to the Roman Catholic Parish in Galantafor kindly and gratuitously permitting any activity connected withthe research.
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