Multi-analytical non-invasive study of modern yellow paints from postwar Italian paintings from the...

Research article

Received: 29 September 2014 Revised: 22 March 2015 Accepted: 22 March 2015 Published online in Wiley Online Library

(wileyonlinelibrary.com) DOI 10.1002/xrs.2623

Multi-analytical non-invasive study of modernyellow paints from postwar Italian paintingsfrom the International Gallery of Modern ArtCà Pesaro, Venice†

Francesca Caterina Izzo,a* Valentina Capogrosso,b Michele Gironda,c

Roberto Alberti,c Chiara Mazzei,a Luca Nodari,e Arianna Gambirasi,e

Elisabetta Zendria and Austin Nevind

We present a multi-analytical non-invasive approach for the characterisation of yellow paints used in three paintings from theInternational Gallery of Modern Art Cà Pesaro, Venice. The paintings selected for this study were executed in oil-based media be-tween 1940 and 1960, they are unvarnished and have largemonochromatic yellow areas. We focus on the identification of yellowpigments with a combined approach based on non-invasive portable X-ray Fluorescence spectrometry, complemented with VISreflectance, remote-Fourier Transform Infrared and Raman spectroscopies. Different yellow pigments including Chrome yellowNaples Yellow and Cadmium-based yellow were identified. Their identification is of fundamental importance because severalmodern inorganic yellow pigments (in particular chrome and cadmium-based pigments) are known to exhibit peculiar degrada-tion patterns, leading to noteworthy aesthetic changes in paint such as darkening and fading. This work highlights the suitabilityof non-destructive techniques for the characterisation of modern paints and the utility of an integrated approach to obtain usefulinformation for preventive conservation. Results demonstrate the need to complement elemental data acquired using portableX-ray Fluorescence with suitable complementary molecular spectroscopic techniques. Copyright © 2015 John Wiley & Sons, Ltd.

* Correspondence to: Francesca Caterina Izzo, Department of EnvironmentalSciences, Informatics and Statistics, Ca’ Foscari University of Venice, Via Torino155/b, Venice, Italy. E-mail: [email protected]

† Presented at the European Conference on X-Ray Spectrometry, Bologna, Italy,15–20 June 2014.

a Department of Environmental Sciences, Informatics and Statistics, Ca’ FoscariUniversity of Venice, Via Torino 155/b, Venice, Italy

b Dipartimento di Fisica, Politecnico diMilano, Piazza Leonardo da Vinci 32,Milan, Italy

c XGLab S.R.L., Spinoff del Politecnico di Milano, Via Francesco D’Ovidio 3, Milan, Italy

d Dipartimento di Fisica, Politecnico di Milano, Istituto di Fotonica e Nanotecnologie(IFN), National Research Council (CNR), Piazza Leonardo da Vinci 32, Milano, Italy

e Istituto per l’Energetica e le Interfasi (IENI), National Research Council (CNR), CorsoStati Uniti 4, Padua, Italy

Introduction

During themiddle of the 20th century, artists were strongly influencedby the introduction of new industrial materials into the art market,which can be appreciated from the wide range of new artistic mate-rials and techniques adopted in painting.[1–4] Commercial formulationsof paint employed traditional pigments, which had been used forcenturies, as well as new synthetic pigments and colorants; in additionstabilisers, extenders and fillers are generally present in manufacturedpaint recipes. Thanks to their availability and low cost, artists used,mixed and experimented with these new paints, even if the long-termstability of new colours were far from being totally understood.[5]

The investigation of 20th century paintings is a challenging anddemanding research field because the variety of materials, theirpotential interactions and their degradation have led to seriousproblems for the conservation of painting collections.[6] The identi-fication of modern paint constituents is essential to better under-stand materials and painting techniques used by modern artistsand to detect potential degradation phenomena, which have beenreported inmodern and contemporary artworks.[7–9] The preventiveconservation of modern and contemporary paintings thus requiresa determination of their composition, using an analytical approach,which should limit sampling (which is a micro-destructive opera-tion), through the use and the development of non-destructiveand non-invasive techniques. This approach should be consideredas a first step in the whole conservation process, providing informa-tion which can inform conservation and prevent the long-termdegradation of susceptible modern art materials. One of the mainadvantages of molecular non-invasive analysis is that it can be used

X-Ray Spectrom. 2015

for monitoring the chemical state of materials over time, leading toa method to assess the state of conservation of sensitive paint.

In recent years, particular attention has focused on modernyellow pigments such as the Chrome yellow (PbCrO4) andCadmium-based yellows (containing Cadmium Sulphides or Cad-mium Sulphur Selenides, or even Cadmapones, coprecipitates ofCadmium Sulphide and Barium Sulphates). As recently reportedfor Van Gogh’s yellows based on Chrome yellow, or Cadmium-based yellows in paintings Matisse and Munch, for example, someyellow pigments easily undergo deterioration.[10–17] Furthermore,their peculiar degradation patterns lead to noteworthy visual

Copyright © 2015 John Wiley & Sons, Ltd.

F. C. Izzo et al.

changes such as darkening and fading, strongly compromising thelegibility and aesthetic impact of paintings.[10,18]

Large scale European infrastructures including mobile laboratorieshave been proposed, which offer an exhaustive range of imaging,molecular and elemental spectroscopic techniques for the non-invasive analysis of paintings and works of art.† There is still a signifi-cant need formethods for themonitoring and analysis of paintings inmuseums, which do not have access to such infrastructures, expertiseand instrumentation. In this collaborative work, we adopt a methodbased on the integration of portable instrumentation, combiningdata fromX-ray Fluorescence (XRF)with a reduced set of complemen-tary spectroscopic techniques for the analysis of three paintingsfrom the International Gallery of Modern Art Ca’ Pesaro in Venice.This work focuses on a multi-analytical non-invasive study of yel-

low paints in three paintings from Ca’ Pesaro collection. The paint-ings selected for this study were executed in oil-based media‡

between 1946 and 1960: Vibrazioni (Vibrations) by Simonetti Masi,La Passeggiata (Walking) by Massimo Campigli and Fiore Giallo (Yel-low Flower) by Guido Gomas (Table 1).The three paintingswere selected based on the following criteria:

the paintings are characterised by the presence of large monochro-matic yellow areas; the works of art are unvarnished, and they havenot been restored in the past. The lack of varnish on the surfacemeans that paint layer is unprotected from light but also meansthat we do not expect interactions with the varnish constituentsand/or the restoration materials in the analysis of yellow paints.Our non-invasive approach combines elemental analysis using

XRF, with molecular (Fourier Transform Infrared and Raman) andelectronic visible (VIS) spectroscopies.X-ray Fluorescence atomic spectroscopy has proved to be valuable

for in situ identification of pigments and a guide for further investiga-tions with complementary analytical techniques.[19–22] XRF is amatureanalytical technique for the determination of the elemental composi-tion of a material. This method is non-destructive, multi-elemental,fast and cost-effective. It can be applied in a non-vacuum environ-ment directly on the sample without any preparation. Over the lastdecade, advances in X-ray generation and detection have led to theevolution of instrumentation from laboratory-based standalone unitsto highly portable and lightweight handheld devices.[23,24] PortableXRF spectrometers have beenwidely adopted in conservation sciencefor the analysis of art.[25–28] However, the interpretation of data re-mains a challenge, and a good understanding of paint and the com-position ofmulti-layeredmaterials is necessary. Indeed, because of thepenetrating nature of X-rays, the interpretation of data from layeredstructures typical for paintings is more complex than other applica-tions such as, for example, the analysis of metal alloys, where it is as-sumed that elements are uniformly distributed and not stratified. Apainting’s structure, ground preparation, paint thickness and pigmentheterogeneity influence the data acquired with XRF. Because themethod identifies elements, pigments with similar elemental compo-sitions cannot be distinguished. In addition, light elements and tracesof pigments in mixtures may not be detectable. For these reasons, amulti-analytical approach is necessary for the analysis of paint.[29]

The result of XRF measurements on yellow paint layers has beencomplemented by other non-destructive and portable analytical

†An excellent example is Cultural Heritage Advanced Research Infrastructures -Synergy for a Multidisciplinary Approach to Conservation/Restoration(CHARISMA), an integrating activity project carried out in the FP7 CapacitiesSpecific Programme Research Infrastructures, www. charismaproject.eu.‡The paintings are described in the General Catalogue of Ca’ Pesaro Gallery as ‘oilon canvas’, although they have never been characterised before.

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techniques, such as VIS reflectance, External Reflection Fourier Trans-form Infrared (ER-FTIR) and Raman spectroscopy with the aim of identi-fying yellow pigments, when possible the class of paint binders and thepresence of inorganic fillers and extenders in the paint formulations.

Instrumental

X-ray Fluorescence spectrawere acquired by using the novel compact,portable and high performances XRF spectrometer ELIO produced byXGLab srl.§ The instrument is characterised by several novel features,which make it particularly well-suited for in situ analysis of works ofart. It is a fast system with Large area Silicon Drift Detector (25mm2)and good throughput capability, thanks to a new complementarymetal-oxide semiconductor (CMOS) Silicon Drift Detector readout(CUBE). ELIO is particularly efficient because of the X-ray transmissiongenerator that can reach up to 50kV and to a high solid detection an-gle geometry. ELIO has a high energy resolution (even below 130eV)and a high low detection limit, which can be coupled with several op-tions of anode tube, filters, collimators (usually 1mm diameter). Agreat advantage of this instrument is its compactness; the detectionhead (2 kg) can be mounted on any light-weight tripod, and it worksin contactless mode. Software provides complete control of the mea-surement head and all information, such as the elemental concentra-tions, the spectra and the images taken by the integrated microscopecamera and the external video camera. For this work, the excitationsource works with an Rh anode, and the beam is collimated to a spotdiameter on the sample surface of about 1.3mm. XRF measurementshave been carried out by fixing the tube voltage at 50 and 15kV ex-ploring a field of analysis from 1 to 40keV.

A CM-2600d Konica Minolta spectrophotometer was used to re-cord reflectance spectra, collected in the wavelength range from360 to 740nm with 10nm resolution. The measurements are in SCI(specular component included) modality. The instrument has eight-degree viewing angle geometry, with Xenon lamp diffusion lightand a high-resolutionmonolithic polychromator. Datawere collectedusing Spectramagic software and elaboratedwith Origin 10 software.

Raman spectroscopic analysis was performed using a handheldXantusTM-1 BaySpec instrument, equippedwith a 785nm laser (band-width from 0.2nm to 0.3nm) and operating from 70 to 500mW. Thespectrometer is customised to cover 500–1800cm�1 range withspectral resolution of 10cm�1. The detector is a 1024 elementcharge-coupled device (CCD) array thermoelectrically cooled to�20 °C. The instrument runs on BaySpec’s Micro 20/20V1038 softwareand has an integratedWindows-based Tablet personal computer (PC).

External Reflection Fourier Transform Infrared spectra were ac-quired by using an Alpha Bruker portable spectrometer operatingin external reflection geometry. Spectra were collected 40 scanwitha resolution of 4 cm�1. The analysed spot has an area of 20mm2.The wide spectral region investigated, from 7500 to 400 cm�1, pro-vides information on both combination and overtones absorptionbands, especially in 7500–4000 cm�1 and on the stretching andbending modes in the medium infrared (MIR) region. All the re-corded spectra show the distortions due to the derivative shape,Reststrahlen effect and intensity enhancement as a consequenceof the optical properties of the investigated substrates.[30]

All the data acquired duringmeasurements were compared witha database of reference artistic materials, both already available inliterature and ad hoc created by the authors.

§For further details: http://www.xglab.it/compact-portable-xrf-spectrometer-elio.shtml.

015 John Wiley & Sons, Ltd. X-Ray Spectrom. 2015

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Table 1. Analysed paintings from the International Gallery of Modern Art Ca’ Pesaro, Venice: detail of yellow painted areas

Author, Title, year Image Detail of yellow analysed area

Simonetti Masi (1903–1969)

Vibrazioni, 1946

Oil on canvas

Massimo Campigli (1895–1971)

La passeggiata, 1955

Oil on canvas

Guido Gomas (1935–2005)

‘Fiore Giallo’, 1960

Oil on canvas

Multi-analytical non-invasive study of yellow paints in postwar Italian paintings

Results and discussion

Analyses were performed on the yellow painted layers of the threepaintings investigated, and close examination did not suggest dark-ening of the paint (see microscopic images in Table 1).

All the results are briefly reported in Table 2, and the discussion ispresented for each painting studied.

¶In the XRF spectra reported in Figs. 1(a)–(c), the labels indicate only K-linelinesand L-linelines (M-linelines are not reported). Characteristic of the presence ofair between the instrument and the sample is the K-lineline of Ar at 2.9 keV. Otherpeaks in the spectrum have been identified with Rh K-lines and L-lines, becauseof the Rhodium tube itself (Rh and Ar peaks are present in all the XRF spectra re-ported in this work, and their presence will not be explained further).

‘La passeggiata’ by Massimo Campigli

The XRF spectrum on a yellow area of ‘La passeggiata’ is reported inFig. 1(a). The most intense peaks are given by Zn K-lines and PbL-lines. Sb, Ca and Fe are also present. Furthermore, traces of Baand Cr have been detected. The presence of S can only be assumedbecause of the limitations of XRF in the detection of lightelements.[31] In fact, besides the inefficiency of the fluorescenceprocess and the weakness of the secondary radiation respect to

X-Ray Spectrom. 2015 Copyright © 2015 John Wiley &

the primary beam, the secondary radiation from lighter elementshas a low penetrating power and is severely attenuated if the beampasses through air for any distance.[26] The quantification of S in thisspectrum is compromised by the dominant presence of Pb, whoseM-line peak at 2.3 keV¶ is close to S K-line, and it is therefore not triv-ial to decouple these two contributions.

From XRF analysis, we deduce that the yellow paint maycontain a mixture of Naples yellow Pb3(SbO4)2 and Chrome yellow(lead chromate, PbCr1-xSxO4). The detection of a significant

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Table

2.XRF,vis-RS,Raman,ER-FTIR

results

from

theanalysed

yellowpaintedareas

Paintin

gXRF

(elemen

ts)*

Vis-reflectan

ceRaman

ER-FTIR

Com

men

ts

Zn

PbBa

Ca

FeSb

Cr

SCd

Sr

Cam

pigli

x*x*

xx

xx

xx

xSh

oulder

centred

atab

out400nm;slight

increase

between450an

d500nm

;sharp

increase

from

550nm

Nap

lesyellow

Chromeyellow

Mixture

ofNap

lesyellowandChromium

yellowin

dryingoil;lithop

onean

dlead

white

inthegrou

nd

layers;calcium

carbon

ateandbarium

sulpha

teas

extendersin

thepaintform

ulation

Bariu

msulphate

Nap

lesyellow

Calcium

Carbon

ate

Calcium

Carbon

ate

Lead

carbon

ate

Dryingoil

(Dryingoil)

Masi

x*x*

x*x

xx

xInitialincrease

from

360nm;lineartren

d

upto

abou

t450nm

;inflexion

centred

atab

out500nm

Cad

mium

yellow

Cad

mium

yellow

Cad

mium

Yellowor

Lemon

yellowin

dryingoil

calcium

carbon

atean

dbarium

sulphateas

extenders

Bariu

msulphate

Calcium

Carbon

ate

Calcium

carbon

ate

Bariu

msulphate

Dryingoil

Dryingoil

Gom

asx*

x*x

xx

xx

xStrongab

sorptio

nup

to500nm

;slight

increase

andainflexion

betweenab

out570

and600nm;lineartren

dfrom

600to

740nm

/Chromeyellow

Chromeyellowbased

paintspread

onapreparation

layerof

lithop

one

Gyp

sum

Binder

not

iden

tifiedsurely

Calcium

Carbon

ate

Dryingoil?

Protein?

*Th

easterisksymbol

indicates

that

theelem

entisdom

inantin

theXRF

spectrum

.

XRF,X

-ray

Fluo

rescen

ce;ER-FTIR,ExternalRe

flectionFourierTransform

Infrared

;vis-RS,vis-reflectan

cespectra.

F. C. Izzo et al.


concentrations of Zn and Pb and of traces of Ba can be explainedwith the presence of a preparation layer of lithopone (copreciptateof ZnS+BaSO4) or the presence of ZnO and BaSO4 and possiblylead white (Pb(CO3)2*PbO2 used in the ground layer.

The vis-reflectance spectra spectrum of the yellow paint isdisplayed in Fig. 2. The reflectance spectrum shows the typicalsigmoidal trend of yellow pigments, with a first shoulder centredat about 400nm followed by a slight increase between 450and 500nm and a sharp increase in reflectance from 550nmapproximately.[32] According to the literature[33] and a database ofmodern pigments created by the authors, the use of both Naplesyellow and Chrome yellow is feasible. However, the informationobtained does not allow the distinction between the different na-ture of yellow pigments, likely because the technique is limitedby the compositional complexity, the non homogeneity of theyellow paint layer and the presence of an organic binder.[32]

External Reflection Fourier Transform Infrared analyses suggestthe presence of Naples yellow highlighted by Raman spectra, asdisplayed in Fig. 3(a) and (b). In fact, the absorption centred at668 cm�1 could be ascribed to Naples yellow, Pb2Sb2O7, in agree-ment with published data[34] and with the comparison with a stan-dard (Naples yellow from Lechler, first half of 20th century) asreported in Fig. 3(d). This attribution is supported by the XRF,Raman and vis-reflectance spectra investigations. Nevertheless,the presence of carbonate compounds cannot be excluded a priori.Among the various CO3

= compounds, only cerussite shows ν4 aclose to 668 cm�1 (i.e. 680 cm�1, reported in Fig. 3(d)). A carefulanalysis of the recorded spectra does not show any other bands at-tributable to PbCO3, supporting the presence only of Naples yellow.Vice versa, weak signals due to CO3

= overtones and combinationbands (ν1 + ν3, ν1 + ν4 and/or 2 ν2 + ν4) are evident (see fig. 3.e) inthe region between 2800 and 1750 cm�1.In fact, the clear shoulderin the C=O absorption, at 1796 cm�1, together with the weak bandat 2512 cm�1 (with a shoulder at 2594 cm�1) can be ascribed to thepresence of calcium carbonate, as suggested by Miliani et al.[30]

The presence of CaCO3 was also observed in Raman spectrawith a band at around 1082 cm�1 related to the stretching of�CO3

2�group and in Infra-red (IR) spectra with the doublet at1048 and 1052 cm�1 arising from the factor-group splitting ofthe ν1 symmetric stretching mode of the�CO3

2� ion. Calcium car-bonate is likely present in the paint formulation as an extender,which is commonly found in the analysis of modern paints.[35,36]

Despite the general difficulty of identifying Naples yellowthrough Raman analysis[37] and the fluorescence because of the or-ganic medium, the Raman spectrum shown in Fig. 4(a) suggests thepresence of lead-antimonate yellow through its characteristic Pb–Omodes at 519, 652 and 810 cm�1[38,39] (it is noted that the bandsvisible at 71, 143, 294, 335, 45 are not included in themeasurementrange with the handheld instrument). Furthermore, the Ramanspectrum highlights the presence of Chrome yellow, thanks tothree bands in the Cr–O stretching region at 825, 841 and856 cm�1; the most visible band is the one at 841 cm�1, which isassigned to the ν1 symmetric stretching vibration.[40] The bands at617, 647 and 988 cm�1 could indicate the presence of BaSO4, as re-ported in Burgio and Clark.[41] For the latter, it is not clear if there ispure barite or lithopone, because the bands related to ZnS, are gen-erally visible at around at 200–400 cm�1 are weak and not recordedby the instrumental range used in this study.

The binder of the yellow paint was identified as a drying oil byspectroscopic analyses. In Fig. 4(a), there are two intense Ramanbands at about 1050 and 1120 cm�1, which may be attributed toC–O–H bending and C–O stretching, respectively. There is also a


Figure 1. (a) X-ray Fluorescence (XRF) spectrum (reported in linear scale) acquired on the yellow area of ‘La passeggiata’ by Massimo Campigli; (b) XRFspectrum (reported in linear scale) acquired on the yellow area of ‘Fiore Giallo’ by Guido Gomas; (c) XRF spectrum (reported in linear scale) acquired onthe yellow area of ‘Le vibrazioni’ by Simonetti Masi.


X-Ray Spectrom. 2015 Copyright © 2015 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/xrs

Figure 2. Vis-reflectance spectra of yellow painted areas from ‘Lapasseggiata’ by Massimo Campigli, ‘Fiore Giallo’ by Guido Gomas and ‘Levibrazioni’ by Simonetti Masi (acquired in specular component includedmodality).

F. C. Izzo et al.

band at 947 cm�1 in the Raman spectra assigned to skeletalmode vibrations of the α-1,4 glicosidic linkage (C–O–C).[42,43]

The other reference peaks between 800 and 1700 cm�1[44] arenot clearly visible, probably because of the luminescence ofthe painting matrix.As visible in the IR spectrum of Fig. 3(a), and in comparisonwith a

reference siccative oil 3 f, the use of a lipidic binding media is con-firmed by the C=O asymmetric stretching absorption togetherwith the overtones and combination bands in the Near Infra-red(NIR) region.[45] The region above 3000 cm�1 clearly shows these

Figure 3. External Reflection Fourier Transform Infrared spectra representativeSimonetti Masi; (c) ‘Fiore Giallo’ by Guido Gomas; (d) comparison among the Passolid line), PbCO3 (dark blue dash line) and Pb3(CO3)2(OH)2 (dark blue dot line) iMasi (red line) andGomas (blue line) spectra in the 3000–1700 cm�1 region. In thbans are reported (CC, calcium carbonate; hCer, hydrocerussite; Cer, cerussite; anline) and the collected spectra in the 6500–2500 cm�1 region (I: first δC-O overtonsiccative oil); in the box, the C =O region is enhanced.


combination bands and overtones. These broad absorptions areattributable to the first overtone of ester carbonyl stretching band(5146 cm�1) to the first and the second CH2 stretching overtone(5787 and 5674 cm�1) and to the combination of methylenicC–H stretching and bending (4329 and 4259 cm�1). In the4000–400 cm�1 region, the main stretching bands of a dryingoil are detected. In addition to the ester carbonyl stretching, witha typical derivative shape with a flex centred at 1748 cm�1, theabsorption of C–H stretching (2961–2864 cm�1) and C–O esterstretching (1126 cm�1) was recognised.

Painting: ‘Le vibrazioni’ by Simonetti Masi

The XRF spectrum on the yellow area of ‘Le vibrazioni’ by SimonettiMasi is reported in Fig. 1(c). The most intense peaks are Zn and CaK-lines and Ba L-lines. Cd and Fe are also present. Traces of Sr havealso been detected. The presence of S, unlike the previous spec-trum, is more reliable, because in this area Pb is not present.

A reasonable hypothesis of the paint composition from XRF datais the assignment of this pigment to Cadmium yellow (CdS) orLemon yellow (CdxZn1-xS)mixedwith BaSO4. BaSO4may be presentin various formations: as an extender, as a coprecipitate with CdS or,together with ZnS, as lithopone.

As seen in the previous case study, the reflectance spectrum re-ported in Fig. 2 shows a sigmoidal behaviour typical of yellowpigments.[32,46] The reflectance has an initial increase from about360nm, follows in a linear trend up to about 450nm before pre-senting an inflexion centred at about 500nm. While no specificassignment can be made to a specific yellow pigments, the reflec-tance behaviour is similar to the reflectance spectrum of CdS.

of the yellow area in: (a) ‘Passeggiata’ byMassimo Campigli; (b) ‘Vibrazioni’ byseggiata and pure Naples yellow from Lechler (orange line), CaCO3 (dark bluen the 1000–400cm�1 range; (e) comparison among the Campigli (back line),e spectra, the position of carbonate and sulphate overtones and combinationd Bar, barite); (f) comparison between linseed oil fromWinsor & Newton (greye, II νs + δ and νa + δ combination bands of the carboxylic component of the


Figure 4. Raman spectra recorded on yellow areas: (a) ‘La Passeggiata’ byMassimo Campigli; (b) ‘Vibrazioni’ by Simonetti Masi.


The Raman spectrum (Fig. 4(b)) confirms the hypothesis basedon XRF data about the yellow pigment and the other constituentsof the paints: the characteristic resonance of Cadmium yellow at600 cm�1[47,48] and the presence of BaSO4 (pure or as a componentof lithopone)[41] are reported in Fig. 4(b).

External Reflection Fourier Transform Infrared spectra collectedfrom the painting ‘Vibrazioni’ (Fig. 3(b) and (e)) show weak CaCO3

combination bands at 1800 and 2512 cm�1. As seen in ‘LaPaseggiata’, calcium carbonate is likely an inert material introducedin the paint formulation. In addition, the weak bands between ν1+ ν4 and ν1 + ν3 of CaCO3 can be ascribed to the presence of BaSO4;they originate from the combination of the SO4

= stretching modes,thus 2ν1, at ≈1965 cm�1, and ν1 + ν3, at about 2190, 2132 and2064 cm�1. The presence of BaSO4 is in agreement with XRF andRaman data.

Similarly to ‘La Passeggiata’, the binder might be identified as alipidicmedium, thanks to the strong peak at around 940 cm�1 asso-ciated to the vibration of α-1,4 glicosidic linkage (C–O–C) and thoseat around 1050 and 1120 cm�1, visible in the Raman spectrum ofFig. 4(b). The typical IR combination bands, overtones andstretching bands of a drying oil can be observed on collected spec-tra, as reported in Fig. 3(b) and (f).

Painting: ‘Fiore Giallo’ by Guido Gomas

The XRF spectrum on yellow area of ‘Fiore Giallo’ by Guido Gomas isreported in Fig. 1(b). This spectrum, as the one from ‘La Passeggiata’,is dominated by the presence of Zn and Pb. Considerable amounts


of Ca, Cr, Ba and Sr are also present with traces of Fe and, probably,of Ba. Among light elements, S is present also in the yellow area, butthe estimation of the concentration of S in the presence of Pb is nottrivial.

X-ray Fluorescence data suggest that the yellow is Chrome yel-low (PbCrO4) spread on a preparation layer of lithopone.

In the reflectance spectrum on yellow area, reported in Fig. 2, thetrend is slightly different from the previous cases. It has a strong ab-sorption up to 500nm, followed by a slight increase in reflectancewhich stabilises at around 550nm and then up forming a slight in-flexion between about 570 and 600nm. From 600 to 740nm, thespectrum continues in a linear trend. This pattern is a characteristicof Chrome yellow.[32]

As seen for ‘La Passeggiata’, PbCrO4 was identified thanks to theν3 of PbCrO4 at 871, and 820 cm�1 was detected by ER-FTIR. TheER-FTIR spectra of yellow area in ‘Fiore Giallo’ slightly differ fromthe ones described earlier (Fig. 3(e) and (f)). The spectrum is dom-inated by strong absorption, inverted by reststrahlen effect, below1700 cm�1. The position of these bands, together with the sharpOH stretching, can be ascribed to the presence of gypsum,CaSO4·2H2O. According to Miliani,[30] the double degenerated ν4,centred at 601 and 676 cm�1, ν3, centred at 1126 cm�1, the sharpδ and ν due to the lattice water, at 1618 and 3521 cm�1 respec-tively, were detected. Moreover, weak combination bands ofCaCO3 were also recognised.

Because of the roughness of the painted surface and the lumi-nescence of the painting matrix, the Raman spectrum (not re-ported) did not allow the identification of pigments and binders.

In the ER-FTIR spectrum, the signal of a C=O ester-bearing com-pound is observable at 1742 cm�1, together with the aliphatic CHstretching bands (Fig. 3(c)–(f)). Furthermore, the weak combinationbands in the NIR region could be ascribed to methylenic bendingand symmetric and asymmetric stretching and the first C =O over-tones. However, notwithstanding the evidence of these absorp-tions, a definitive identification of the paint binder is not possiblebecause of the low intensity absorption in both MIR and NIR re-gions. The identification of the binder would require samplingand analysis using chromatographic techniques.

Conclusions and future perspectives

In this study, yellow pigments, paint binders and extenders in thepaint formulations of paintings of the International Gallery of Mod-ern Art Ca’ Pesaro, Venice, were analysed in situ, non-destructivelyand effectively identified using portable and versatile analytical in-strumentation. Identification and interpretation of the obtained re-sults were supported in comparison with the literature and analysisof reference samples. In particular, XRF data were complementedby other non-destructive and portable analytical techniques, suchas VIS reflectance, ER-FTIR and Raman spectroscopy.

X-ray Fluorescence measurements have been carried out onareas of yellow in different paintings and provide elemental infor-mation crucial for distinguishing different materials and mixtures.In all paintings analysed, XRF revealed the presence of Zn, Pb, Ba,S and Ca, but signals from these elements vary, and can be attrib-uted to the preparation layer and the presence of fillers in paint.While some yellows contain both Zn, Pb and S, other diagnostic el-ements can be useful for the attribution of specific yellow pigmentsin the paintings studied; here, the presence of Cd and Cr (in combi-nation with Zn and S, or Pb, respectively), suggests the presence ofCd-based yellows or Lead chromate.


F. C. Izzo et al.

The identification of Lead chromate, which is known to degradeand change colour in time is particularly important for the develop-ment of suitable exhibition, storage andmonitoring of paintings. Inaddition, the presence of Cadmium-based yellows calls for long-term monitoring of the paintings because of the recently reportedalteration of early 20th century paintings.While a non-invasive approach can answer many technical ques-

tions regarding paintings, the stratigraphy, composition of theground and the identification of specific binding media requirecareful sampling, the preparation of cross-sections and analysis ofsamples using suitable methods for the detection of organic mate-rials and trace impurities.[49] In the future, data from spectroscopicanalysis from specific areas of paintings will be integrated withimaging-based analysis and information acquired through the anal-ysis of paint samples.

Acknowledgements

The authors express their thanks to Dr. Matteo Piccolo of the Inter-national Gallery of Modern Art in Ca’ Pesaro (Venice) for the interestdemonstrated for the study and the interaction between art andconservation science.

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