Journal of Cultural Heritage 8 (2007) 289e293http://france.elsevier.com/direct/CULHER/

Case study

Painting technique and state of conservation of wall paintingsat Qusayr Amra, Amman e Jordan

Sara Bianchin, Umberto Casellato, Monica Favaro, Pietro Alessandro Vigato*

Istituto di Chimica Inorganica e delle Superfici (ICIS) e CNR, Corso Stati Uniti, 4, 3512 Padova, Italy

Received 5 September 2006; accepted 3 May 2007

Abstract

The state of conservation of the frescoes at Qusayr Amra was investigated by integrated physico-chemical measurements, particularly opticaland scanning electron microscopy, m-infrared spectroscopy, mass spectrometry and X-ray powder diffraction.

The frescoes appear darkened and severely damaged owing to the deterioration of surface treatments and to the widespread presence of dif-ferent salts. These caused significant detachments of the painting layers.

The materials used in the painting and preparation layers and in the wall plaster were characterized in order to clarify the painting technique.Different pigments have been identified on the pictorial layers: the original ones correspond to green earth, yellow and red ochre, realgar, boneblack and lapis lazuli and others, such as titanium white and cobalt blue, ascribed to recent restoration works. Proteinaceous materials (egg oryolk) have been identified as binders for the pigments, indicating a tempera painting technique.

Three different products, belonging to restoration interventions, have been also identified: the natural product shellac, ascribable to next-to-last restoration and scarcely removed during last restoration also because of its insolubility, the synthetic vinyl acetate and acrylic polymers.Particularly the latter one indicates an on-going degradation of the applied fixatives.

The extensive deterioration of the surfaces is also due to the widespread presence of salts, such as chloride, nitrate and sulphate clearly iden-tified by XRD measurements.

The obtained results give a comprehensive overview on the employed painting technique and its state of preservation and on the causes of thepainting deterioration. Therefore, they are a fundamental tool to develop durable and compatible materials and methodologies for a future con-servation strategy of this site.� 2007 Elsevier Masson SAS. All rights reserved.

Keywords: Wall paintings; State of conservation; Organic fixatives; Efflorescence

1. Aim of the research

Integrated physico-chemical investigations were carried outon fragments, collected from the pictorial cycle at QusayrAmra, one of the most important buildings of the Umayyaddynasty (750 A.D.) in Jordan, with the aim to obtain useful in-formation about the painting technique, to offer a preliminaryscientific view of the state of conservation of these wall paint-ings, to ascertain the type and the extent of the degradation

* Corresponding author. Tel.: þ39 049 829 5962; fax: þ39 049 870 2911.

E-mail address: vigato@icis.cnr.it (P.A. Vigato).

1296-2074/$ - see front matter � 2007 Elsevier Masson SAS. All rights reserv

doi:10.1016/j.culher.2007.05.002

processes and to detect the materials used in previous interven-tions. The final goal is to offer scientific tools for a better un-derstanding of this pictorial cycle and to set up a scientific aidand guide for a conscious intervention on these paintings,severely damaged not exclusively by natural decay processes.

2. Introduction

As other desert castles, Qusayr Amra was built during thedynasty of Umayyad Caliphs (661e750 A.D.) [1,2]. QusayrAmra was a residence of vacation or a place for rest and there-fore equipped with baths. In fact, the Arabic term ‘‘qusayr’’

ed.

290 S. Bianchin et al. / Journal of Cultural Heritage 8 (2007) 289e293

Fig. 1. (a) View of the ‘‘Desert Castle’’ at Qusayr Amra; and (b) a painted vault showing different deterioration features.

indicates a Roman style villa with a piece of land for growing.Also a facing wall has been found in the proximity of the bot-tomland (wadi), which suggests a settlement devoted to agri-culture (Fig. 1). Very important mural paintings decorate thecentral hall and the connected rooms of the building of QusayrAmra, destined to alcoves and baths with tepidarium and cal-idarium. Although they have been recently restored, the paint-ings appear severely deteriorated. The low part of the paintings(originally painted as imitation of marbles) are damaged bythe rising damp and worsened by writings, incisions and othervandalic actions, that have caused the total loss of significantparts of them. Besides all, chromatic alterations are widelydistributed, essentially greyish in colour that could be ascribedto the deposition of soot and other atmospheric fine particu-lates. Moreover, many areas show an extensive network of mi-cro-cracks associated with a spread darkening of the paintedsurface and detachments; this peculiar decay pattern is espe-cially localised on paintings subjected to earlier restorationsby different organic fixatives [3].

The frescoes of Qusayr Amra show details of the clothes,i.e. the colors and the fabrics, that testified the social and eco-nomic life in the Umayyad period. Today the visitor must usehis imagination to reconstruct the original aspect of the paint-ings because of the very poor state of presentation of manyscenes, as a diffuse dark patina overshadows the restoredpainted surfaces. An urgent restoration is needed to adequatelyclean and free from the dirt the wall paintings.

3. Experimental

Twelve samples areas have been collected from the westernand northern walls, side-walls with respect to the main en-trance. The sampling procedure deserved difficulty owing tothe scarce cohesion of the painting layers and the crumblingof the plaster. The samples were observed as received and ascross-sections. The optical observations on the cross-sectionwere carried out by a microscope Olympus BX51 equippedwith UV-light source to prove the organic layers. The crosssections were analysed also by SEM-EDS, after metallizationthrough the deposition of a graphite film. The instrument wasPhilips Model XL 40 LaB6. Semi quantitative analyses of

elemental composition were obtained using an EDAX DXPrime X-ray energy dispersive spectrometer equipped witha thin beryllium window, using an accelerating voltage of25 keV.

By stereomicroscope observation of the collected samples,the different layers of the paintings have been mechanically sep-arated each others and studied separately. The binding media ofthe painting layers were identified by mFTeIR analyses, per-formed either on the different crushed layers and on their solu-ble fractions extracted by solvents (CH2Cl2, H2O, EtOH,Acetone). IR spectra were collected in reflection mode bya Nicolet Magna IR560 FTeIR Spectrometer and SpectraTech microscope on the separated layers and the extracted frac-tions flattened on a gold surface. The IRUG database was usedfor the identification of the material constituents of the samples[4]. X-ray diffraction (XRD) analyses of the ground sampleswere performed on a Philips X’Pert PW3710 diffractometer, us-ing Cu Ka radiation (40 kV, 30 mA), high-resolution graphitemonochromator, rotating sample holder and proportional detec-tor. Measurements were carried out in the range 5� < 2q < 90�

with a step of 0.02�; the ICDD data bank of standard X-ray pow-der spectra was used for phase identification [5].

4. Results and discussion

The collected samples have been examined as received and/or as cross sections by integrated physico-chemical measure-ments, particularly optical and scanning electron microscopy,mFTeIR and, where possible, by X-ray powder diffraction inorder to verify the pictorial technique, the state of conservationof the frescoes, the damages caused especially by chemicallyagents, particularly salts, detachments, repaintings and fixa-tives also in consequence of the materials employed in previ-ous interventions and to propose an appropriate interventionproject. Some Pyrolysis GCeMS measurements have beenalso included to corroborate the infrared indications aboutthe organic materials.

Optical and SEM-EDS microscopies show that the finishingplaster below the painting layers contains calcium carbonateand a small amount of Si, mainly in the form of quartz clus-ters. Some samples show a superficial finishing layer,

291S. Bianchin et al. / Journal of Cultural Heritage 8 (2007) 289e293

Fig. 2. Cross section of sample G4a2, magnification 500�. Optical observation shows the finishing lime layer followed by the blue layer composed of calcium

carbonate and particles of natural lapislazuli and two superimposed restoration layers (a). Observation by UV light evidences the fluorescence on original and

restoration layers due to organic materials (b).

exclusively constituted by Ca (white lime). Mineral and syn-thetic inorganic pigments have been identified on differentpainting layers: green earth (potassium and iron silicate),bone black, natural lapislazuli, red and yellow ochres, realgarand white lead [6e8] (Fig. 2). With the exclusion of layerscontaining white lead, the widespread distribution of Ca onthe painting layers proves the use of lime as a binder; notwith-standing organic binding as egg tempera, has also beenemployed as identified by mFTeIR and GCeMS investiga-tions. Industrial pigments as cobalt blue and titanium dioxide[8] have been also identified; they clearly belong to a pictorialretouching performed during recent interventions.

mFTeIR investigations, carried out on powders collectedfrom the different painting strata, gave quite convincing infor-mation on the original binding materials and the organic prod-ucts applied as restoration fixatives; spectra collected on

several samples show a carbonyl ester band at 1738 cm�1 (nC]O stretching) and the protein bands (broad band centredat 3308 attributed to stretching n N-H, 1650 stretching nC]O amide I and 1543 cm�1 bending d N-H amide II)(Fig. 3a) [9]. The comparison with reference spectra and thedata obtained by pyrolysis GCeMS investigations indicatethe presence of egg [10]. Absorptions of calcium oxalatebands at 1618 and 1316 cm�1, respectively the symmetricand asymmetric stretching of COO group [11] and absorptionsof nitrate salts at 1386 and 837 cm�1 (Fig. 3b), respectivelythe stretching and out-of-plane bending of NO3

� group [12]are clear indication of transformation of constituent materialsand salt induced decay processes.

The mFTeIR characterization of powders and CH2Cl2 ex-tracts from the superficial layers of painting samples showsdifferent absorption patterns: some spectra, collected from

(a)

0,0

0,1

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0,4

Abs

(b)

-0,0

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Abs

(c)

0,05

0,10

0,15

Abs

1000 2000 3000 4000 Wavenumbers (cm-1)

Fig. 3. FTeIR spectrum of the CH2Cl2 soluble fraction of the sample G3 (a) and of the H2O soluble fraction of the sample G8 (b, c). Infrared absorptions reflect the

composition of proteinaceous binding media (i.e. animal glue, egg) in the painting layers (a) and the presence of nitrates (b) and oxalates (c) due respectively to

transformation of constituent materials and salt induced decay processes.

292 S. Bianchin et al. / Journal of Cultural Heritage 8 (2007) 289e293

the outmost layers, show a strong absorption at 1739 cm�1 dueto the n C]O carbonyl stretching of an ester group, intensebands at 1235 cm�1, corresponding to the C-O stretchingband of the acetate CH3-CO-OR, and at 1021 cm�1, corre-sponding to the O-C stretching of the acetate group O-CH2

[13] (Fig. 4a). This characteristic absorption pattern is ascrib-able to a vinyl acetate polymer, in good agreement with thereference spectrum of the commercial synthetic resin poly(eth-ylene/vinyl-acetate) (BEVA 371), widely employed in the re-cent past as fixative for mural paintings and canvas [14,15].

Acrylic polymers have also been identified on superficiallayers of few samples (Fig. 4b), these may be ascribed tothe commercial product Primal, applied during the last resto-ration work. More remarkably, the IR spectrum of the acrylicpolymer shows a weak band occurring at 1776 cm�1 related tostretching absorption of g-lactones (Fig. 4b), a common fea-ture of polymer photo-oxidative degradation [16,17], indicat-ing the applied product is undergoing severe deteriorationprocesses.

Several samples also show a brownish superficial layer,which appears bright fluorescent by UV light observation ofcross sections (Fig. 2b) and consequently not ascribed toa polymer used as restoration material. So far, it has been me-chanically separated from the painting fragments and charac-terised by mFTeIR. All attempts to solubilise it withdifferent solvents (CH2Cl2, acetone, H2O, CH3CH2OH) failed.The IR spectra, collected on the insoluble brownish product,show a strong band occurring at 1712 cm�1 with a shoulderat 1732 cm�1, related respectively to antisymmetric C]Ostretching of a carboxylic acid and to n C]O stretching ofan ester group. Other bands in the range 1300e1150 cm�1

can also be attributed to different stretching modes of the esterand acid groups, while absorptions at 2929 and 2856 cm�1 arerelated to asymmetric and symmetric stretchings of CH3 and

CH2 groups [13] (Fig. 5). The mixture of esters and acids re-sembles the composition of the natural product shellac, whosereference IR spectrum fully agrees with the analysed unknownproduct [18]. Shellac’s good adhesive power and penetrationmade it widely employed as fixative for wall painting, not-withstanding the yellowing and increasing insolubility withageing that darken the treated surfaces and strongly reducethe removability [15,19].

XRD analyses of samples collected from the widespread ef-florescences, prove the presence of sylvite and halite, respec-tively a potassium and sodium chloride, aphthialite, a mixedsodium and potassium sulfate, and, finally, nitratine, sodiumnitrate. Macroevidences of pulverization of the wall painting,detachments and superficial incrustations, induced by thedisruptive effects of these soluble salts, have been also high-lighted by micro morphological SEM observations on samplescollected from these deteriorate areas.

5. Conclusion

The physico-chemical investigations, carried out on a seriesof fragments, collected from the wall paintings of the desertcastle at Qusayr Amra in Jordan, allowed a comprehensivecharacterization of the pictorial technique and of the natureand the degradation degree of the wall paintings. Different pig-ments have been identified on the pictorial layers: the originalones, corresponding to green earth, yellow and red ochre, re-algar, bone black and lapis lazuli and those ascribing to recentrestoration works, such as titanium white and cobalt blue. Indisagreement with other studies [3], mFTeIR and GCeMSanalyses identified a proteinaceous medium, i.e. egg or yolk,employed as binder for the pigments. mFTeIR spectroscopyhas also identified three different fixatives. The natural prod-uct shellac has been found in several samples ascribable to

(a)

0,1

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1776

(b)

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0,20

0,25

0,30

0,35

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1000 2000 3000 Wavenumbers (cm-1)

Fig. 4. FTeIR spectrum of the CH2Cl2 soluble fractions of the sample G4. Both spectra indicate the presence of restoration polymers applied in the recent past:

a vinyl acetate polymer, in good agreement with the reference spectrum of the commercial synthetic resin poly(ethylene/vinyl-acetate) (BEVA 371) (a) and an

acrylic polymer tentatively ascribed to the commercial product Primal (b). The latter is undergoing severe deterioration processes as indicated by the absorption

at 1776 cm�1, ascribable to g-lactones, a common feature of polymer photo-oxidative degradation.

293S. Bianchin et al. / Journal of Cultural Heritage 8 (2007) 289e293

(a)

0,05

0,10

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(b)

10

2

4

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20003000 4000Wavenumbers (cm-1)

Fig. 5. FTeIR spectrum of powdered superficial brownish layer of painting sample G8 (a). The infrared absorption can be inferred to a mixture of esters and acids,

resembling the composition of the natural product shellac. Its spectrum fully agrees with IRUG reference IR spectrum (b).

next-to-last restoration and scarcely removed during last res-toration also because of its insolubility in the most commonsolvents. It could be responsible of the widespread and se-vere darkening of the wall paintings. Also vinyl acetateand acrylic polymers have been identified on the painted sur-faces and the decay products, especially of the acrylic poly-mers, clearly indicate an on-going degradation of the appliedfixatives.

The pictorial cycle is indeed severely damaged also by solu-ble salts transported by rising damp and ground water; chloride,nitrate and sulphate salts have caused remarkable surface alter-ations, efflorescences and detachments of painting fragments.

The present work must be considered as a preliminary as-sessment to quantify and qualify the degree and type of damagesuffered by wall paintings, to evaluate the current effectivenessof the fixatives applied during the previous restoration and theirpossible alterations. The obtained results clearly show the se-vere deterioration that are suffering both the original materialsand the applied products and must be use as a starting point todevelop durable and compatible materials and methodologiesfor a future conservation strategy of this site.

Acknowledgement

We thank Progetto Finalizzato ‘‘Beni Culturali’’-CNR for fi-nancial support. We are also indebted to Dr. Fawwaz Al-Khrey-sha, director of the Jordanian Authority of Antiquities whomade possible this investigation. We also thank Dr. Bonaduceand Prof. M.P. Colombini for the GCeMS measurements.

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