application of raman microspectroscopy to problems in the conservation, authentication and display...

JOURNAL OF RAMAN SPECTROSCOPYJ. Raman Spectrosc. 2004; 35: 710–718Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jrs.1213

Application of Raman microspectroscopy to problemsin the conservation, authentication and display offragile works of art on paper

David Wise1∗ and Andrea Wise2

1 CCM Programme, University of Canberra, Canberra, ACT 2601, Australia2 Conservation Department, National Gallery of Australia, GPO Box 1150, Canberra, ACT 2601, Australia

Received 5 September 2003; Accepted 24 March 2004

This paper explores the application of Raman spectroscopy to the examination and analysis of a rangemedia commonly found on works of art on paper. In this case all of the works are from the NationalGallery of Australia’s collection. Discussion specifically focuses on the practical benefits that a detailedknowledge of inks and pigments can have for both conservators and curators. Through the use of severalcase studies, different aspects of these benefits are highlighted. Consideration is given to the way inwhich Raman spectroscopy can supplement the commonly used technique of polarized light microscopyin the identification of inorganic and organic pigments. Comparative results using scanning electronmicroscopy–energy-dispersive x-ray spectrometry and Fourier transform IR microspectroscopy are alsodiscussed. Works examined include an important but previously undisplayed pastel drawing by theAustralian modernist painter Grace Cossington-Smith, a sketchbook by the 19th century Aboriginal artistTommy McRae and an early 20th century European lithographic poster. Copyright 2004 John Wiley &Sons, Ltd.

KEYWORDS: Raman micro-spectroscopy; conservation; works on paper; pigments

INTRODUCTION

The analysis of pigments on works of art may be undertakenfor a number reasons. The information revealed by analysiscan enlighten discussions concerning the history of a work.This might include the palette used by the artist, possibleperiod and place of execution, at least in broad terms, and anartist’s original intentions. Pigment analysis can be used todetermine questions of attribution and authenticity and assistwith preserving a work particularly where the pigments thathave been used are fugitive, prone to deterioration or actas catalysts to other deterioration processes. In this paper,discussion is focused on three works of art on paper in theNational Gallery of Australia collection and the way in whichthe information provided by pigment analysis of these workshas fulfilled the demands of conservators and curators andinspired cooperation in determining display strategies forworks whose potential fragility is linked to pigment content.Although Raman microspectroscopy was a focal point in the

ŁCorrespondence to: David Wise, CCM Programme, University ofCanberra, Canberra, ACT 2601, Australia.E-mail: [email protected]

analytical work, a flexible approach was typically taken toproblem solving.

EXPERIMENTAL

Raman spectroscopyAll Raman work was carried out with a Renishaw 2000Raman imaging microscope. The equipment used was fittedwith an air-cooled He–Ne laser at 632.8 nm (Spectra-PhysicsLaser, Model 127) and a near-infrared laser diode at 780 nm;however, only the 780 nm beam was used in this workto minimize fluorescence. The spectrometer uses a Peltier-cooled change coupled device (CCD) detector together witha holographic notch filter and two beam paths the diffractiongrating being at 1800 grooves mm�1 for spectral collectionand an angle tuned dielectric filter path for spectra and two-dimensional image recording. The microscope is an externalOlympus BH-2 with a motorised x,y stage. Naphthalene wasused as a calibration standard, with settings for laser power,accumulation, integration times being varied according tothe sample needs. Samples were analysed either intact orafter brief solvent dispersion.

Copyright 2004 John Wiley & Sons, Ltd.

Raman microspectroscopy of works of art on paper 711

Scanning electron microscopy–energy-dispersivex-ray spectrometry (SEM–EDX)The SEM–EDX unit used was a Cambridge S360. Speci-fications include LaB6, Tracor Northern EDXA detector (Bewindow, 147 eV) with Moran EDXA processing system, four-segment backscatter detector, Oxford CT1500B Cryotranscold stage/coating unit, point-to-point measurement intrin-sic to microscope, high-resolution image store (1536 ð 1152pixels), turbomolecular and sputter on pumps, 70 mm rollfilm, videographic printer video output and ImageSlave1024 ð 768 slow scan image acquisitions.

FTIR micro-spectroscopyThe FTIR unit used was a Thermo-Nicolet Centaurus FTIRmicroscope with an MTB detector in the microscope and a15ð objective linked to a Thermo-Nicolet Nexus bench unit.All samples were prepared on a diamond compression celland spectra gathered through a 50 ð 50 µm aperture.

Polarized light microscopy (PLM)A Leica DM LP microscope with standard polarizingaccessories was used for all PLM work. The microscopeis fitted with N Plan ð10, ð20, ð50, C Plan ð63 objectives, anAplan 0.6 P condenser and HC Plan ð10 Eyepieces. A LeicaDC200 digital still camera interfaced with SIS AnalysSISimage database and analysis software was used for imagedocumentation. Dispersed pigment samples were mountedwith Cargille MeltMount, nD D 1.66 at 25 °C.

CASE STUDIES

Nitrolian: Leonetto Cappiello (Plate 1)The large offset-lithographic poster advertising Nitrolianquick-drying paint was designed by the Italian graphic artistLeonetto Cappiello and printed in Paris in 1929. Cappiellowas at the forefront of advertising art incorporating manydevices that still appear modern to the viewer. The Nitro-lian poster quickly became a collector’s item after its firstpublication, taking it beyond its original advertising hoard-ing destination. The enduring popularity of the work hasled to original copies reaching relatively high prices onresale and a large number of subsequent reproductions havebeen produced through a range of printing processes, vary-ing quantities of which are now in circulation (informationregarding Cappiello as an artist supplied by M. Hensaw,Curator of International Prints, National Gallery of Aus-tralia).

The pristine version in the collection of the NationalGallery of Australia (NGA) was acquired in 2003. It ispurported to be one of the printer’s copies retained fromthe only original edition. Although there was little actualdoubt as to the authenticity of the work, the strong smellof linseed oil retained by the rolled print, the clean whiteappearance of the paper and fabric backing and generalcondition of the inks did raise questions. In other original

copies of the poster the red ‘paint’ in the image is often not asdeep in hue as the NGA version and may appear lighter andmore orange in overall tone. It was of interest to establish apossible cause for this apparent variation, especially if thecause may be due to a susceptibility in the ink to colour shiftsdue to fading.

Initial investigation was carried out by PLM on mounted,dispersed samples and confirmed by Raman spectroscopyon individual particles. This indicated that the blue was afinely divided synthetic ultramarine mixed with chalk. Theblack was composed of a very fine carbon black. In areasof greyer ink the black pigment appeared to be mixed withsubstantial quantities of barium sulfate.

The examination of samples from the light and darkred areas suggested that they were of largely similarcomposition, being a chrome yellow pigment mixed withan organic red and smaller amounts of vermilion (Fig. 1).The samples again included barium sulfate as the syntheticmineral, also known as blanc fixe, and traces of chalk. Onceagain Raman spectroscopy provided confirmation of thePLM results, except in the case of blanc fixe, which, due to itssmall particle size and largely dispersed nature in the sample,was firmly identified only with Raman spectroscopy. Opticalmicroscopy suggested that alterations in colour between thelight and dark areas were achieved by varying the ratiosof organic red and chrome yellow in admixture with thevermilion, rather than by adding white pigment or markedlyincreasing the diluting effect of the barium sulfate and chalk.Both sample areas gave very similar Raman spectra withcharacteristic lead chromate and vermilion peaks, followedby less intense peaks for the organic red pigment in thefingerprint region. The spectrum from a small agglomerationof barium sulfate particles provided stronger peaks in thefingerprint region for the synthetic organic red (Fig. 2). Aftersubtraction of the chromate, vermilion and barium sulfatepeaks and direct comparison against known standardsthe organic red pigment was identified as probably beingPigment Red 49 (Fig. 3).

The PR 49 pigments as a group are ˇ-naphthol lakepigments. PR49 was first developed at the end of the19th century and was especially suited to most commercialprinting techniques, including general-purpose lithographicprinting, hence the common trade name Lithol Red. Itssuitability for printing was due to its good dispersioncharacteristics, high tinting strength, bright vibrant colourand comparative cheapness. However, when consideringworks of art, all PR49 pigments have poor lightfastness andthis is of particular concern in lithographic printing wherethe ink film is generally thin.1 Given the known instabilityof PR49 pigments, it is probable therefore that the variationin colour between the version of the Nitrolian poster in theNGA and other examples is due to the preferential fadingof the PR49 pigment leaving the more light-stable chromeyellow and vermilion pigments dominant in examples whichhave undergone high levels of light exposure.

Copyright 2004 John Wiley & Sons, Ltd. J. Raman Spectrosc. 2004; 35: 710–718

712 D. Wise and A. Wise

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Figure 1. Comparison of Raman spectrum of red ink from Nitrolian poster against known standards (chrome yellow, vermilion).

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Figure 2. Raman spectrum of Nitrolian poster red ink acquired from barium sulfate clump and subtraction.

Portrait of Diddy: Grace Cossington-Smith(Plates 2 and 3)The second case study is an early pastel and charcoal drawingby Grace Cossington-Smith dating from 1922, purchased bythe NGA in the 1970 and unexhibited since that time owingto the extremely fragile nature of the paper support. GraceCossington-Smith was pivotal in the development of modernAustralian art, producing works preoccupied with colour,light and form. This portrait is of Charlotte, her youngestsister, affectionately known as ‘Diddy’. The portrait is drawn

on a laid Arches Ingres-type paper, made in France andwatermarked as such together with the initials ‘MBM’. Thepaper is creamy yellow in tone with a ‘toothed’ surface,a desirable quality for use with a friable medium such aspastel.

In preparing this work for exhibition, the conservationdepartment at the NGA noted the presence of highly local-ized areas of discolouration and enhanced embrittlementof the paper support associated with this discolouration.Although the embrittlement to some extent conformed to



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Figure 3. Comparison of subtraction against PR49 : 1 standard.

delineated areas within the image the affected areas werenot associated with one particular colour and some areas ofdiscolouration, especially the obviously drawn marks alongthe lower edge, were not visibly part of the finished com-position. The degree of visible brown degradation in thesupport is surprising in what we know to be a high ˛-cellulose-containing paper. In addition, the artist utilized apastel medium which is typically supplemented with quan-tities of calcium carbonate. This results in an image layerwhich would be normally expected to have a protectiveeffect on the paper. There was no obvious evidence of pre-vious restoration procedures which might have contributedto the accelerated ageing of the support, such as aggressivebleaching. Also, no media other than the traditional gumswere suspected to be present.

An examination of the pigments that comprise the presentimage areas was carried out by PLM followed by Ramanspectroscopy. This indicated that a fairly limited palettehad been used with pastels being applied over a charcoaldrawing. All of the yellow areas were achieved with mixturesof chrome yellows (primarily lead chromate but possibly alsostrontium chromate), yellow ochre and several burnt earthssuch as burnt sienna. Greener areas of the composition wereachieved by combining the ochres and chrome yellows withPrussian blue. Darker shadows and areas of over-drawingwere carried out with pastel composed of a very fine carbonblack. In the flesh areas there was the addition of a redpigment to give a purer red tone. Unusually for this date,the red pigment was almost wholly red lead in combinationwith small amounts of vermilion (Fig. 4). It is probablyfound here as a matter of pure economics, replacing therelatively more expensive vermilion pigment with a cheaper,

similarly coloured although less stable material.2 As wouldbe expected with a pastel medium, all of the pigments wereheavily adulterated natural chalk and small amounts ofbarytes.

In cross-sections from degraded and undegraded areasof the image, it was obvious that a thin, brighter white,pigmented layer underpinned several of the overlaid yellow,black and brown layers (Fig. 5). The presence of thispreparatory white drawing appeared to coincide with areasof heavy degradation in the support. It was suspected fromthe PLM analysis that some of the samples, especially thosefrom the particularly degraded areas, contained zinc white.However, this was unable to be confirmed by Raman analysisowing to the substantial fluorescence and interference fromthe binding medium masking the relatively weak zincoxide peaks. Samples from the unaffected areas did nothave this initial white preparatory layer and in fact allwhite highlights currently visible on the image contain onlycalcium carbonate.

Representative cross-sections were analysed withSEM–EDX, which indicated that the white preparatory layercontained barium sulfate and zinc. The barytes particlescould be easily seen by optical microscopy, but were alsoreadily visible in the backscattered image owing to theirhigher molecular weight and distinctive form. Zinc waspresent in all EDX spectra collected from the intersticesbetween the barytes particles, although no discrete particleswere observed (Fig. 6). This layer is unusual on the drawingas, although barytes is observed in mixtures with the otherpigments, elsewhere it is present in very small amounts withchalk being used as the main diluent. Here chalk is a minorcomponent with barytes making up at least 50% of the overall



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Figure 4. Raman spectra of orange/red pigment from flesh tone.

Figure 5. Cross-section through degraded support showingwhite layer below present image.

mixture. Zinc was not found in combination with the upperchalk layers.

It is known that certain pigments can cause accelerateddegradation of cellulosic materials, especially paper, throughautocatalytic processes. This has been documented withcopper(II) ion-bearing pigments such as malachite, verdigrisand emerald green.3 A similar problem has also been notedwith zinc oxide pigment.4

Although it cannot be stated categorically that thedeterioration observed in this drawing is the result of zincoxide catalysis, it remains a significant possibility. This isespecially so given the pattern of the deterioration andthe absence of other known causes of discolouration andembrittlement in paper. Moisture has been present at variousstages in the life of the work, either through direct contact orpersistent damp storage and display. The thin open structure

Figure 6. SEM image of pigment layers: left-hand side, Fig. 5.Upper layers show concentration of calcium, lower layerspredominantly barium. Zinc found in dark areas betweenbarytes particles.

of the drawn layer and its particulate nature would besufficient to allow penetration of light through to the lowerlayers and the support. Although the exact mechanism for thereaction is not fully explained, both are recognised elementsnecessary for the initiation of zinc ion-induced hydrogenperoxide production and accelerated scission of the cellulosechains in the paper support.5



Recognition of the pattern of deterioration as being inher-ent to the materials in the object has been important indesigning a suitable treatment strategy. This has meant lim-iting aqueous treatments due to the migration of acidityfrom the paper support, potentially disastrous for a drawingmedium containing substantial quantities of calcium car-bonate. The proposed problem with the zinc white contenthas also been important in considering framing and makingrecommendations for display and storage of the work.

Sketchbook: Tommy McRae (Plates 4 and 5)The third case study concerns the problem of displaying aunique and culturally significant item of unknown thoughpotentially suspect stability. The sketchbook of drawings byTommy McRae is a very rare artefact. Probably executedduring the 1880s, the drawings record aspects of traditionalAustralian Aboriginal life seen through the eyes of anAboriginal artist working in a European style. Such recordsare irreplaceable as they often represent the only visualknowledge we now have of particular details of the dailylife of Aboriginal peoples. McRae is also unusual in sofar as the drawings were all completed towards the endof his life and the aspects of traditional life he wasrecording had already changed markedly. These changes areacknowledged by the inclusion of Europeans and Chinesefigures in his sketches together with the suggestions ofmodern industrialized society.6 The sketchbook itself isexceptional in being virtually complete and in very goodcondition and, although a few of the sketches have beenpublished previously in reproduction, the book itself hasvery seldom been on display.

The materials that Tommy McRae used are recorded ashaving been sourced from local stationery shops in countryVictoria where he lived rather than an artist’s supplier.7 Thesketchbook is in fact a small, hardbound pocket notebook, notan artist’s sketchbook in the traditional sense. The drawingsare executed in a simple range of colours, a black, blue, vividpink and violet. As the sketchbook appears to have been keptclosed for the majority of its life, the colours are relativelybright and clear. The only notable change is in the black,which shows obvious signs of the deterioration patternsassociated with iron gall inks, discolouration of the supportsurrounding the ink and a colour shift from black to brown.It is reputed that although Tommy McRae generally used hismaterials unaltered, he did however add to his iron gall inkin unspecified ways. Problems with the analysis of iron gallink will not be discussed in depth here. The iron gall ink inthe sketch books is thinly applied and has become stronglyintegrated into the structure of the paper during on-goingdegradation. Spectra aiding in the identification of the inkcould not be obtained by either Raman or FTIR spectroscopy,supporting somewhat the problems experienced by otherresearchers as outlined by Sistach and Ferrer.8

A large proportion of the sketches are executed wholly ineither black, blue or violet inks, with the greater proportion

being in either blue or violet. The pink ink is used onlyoccasionally and is typically found underlying one of theother inks. Analysis was initially carried out by Ramanspectroscopy directly from the images in the sketchbook,followed by further analysis on single fibre samples. Theresults were unfortunately variable. The iron gall ink, pinkand violet showed extreme fluorescence with no indication ofany characteristic peaks. Enhancement techniques, includingSERRS, were tried but no improvement in the Ramanresponse could be gained. Standard SERRS solutions wereobtained from Foster Freeman and used according to therecommended procedure on known samples and samplesfrom the McRae sketchbook. More success was achieved withthe blue, which was identified as being based on Prussianblue (Fig. 7).

Given the date of the sketchbook, the physical appearanceof the pink and violet and the reputed source, the rangeof materials on which they were likely to be based isrelatively limited. As the inks are most probably cheapcommercial inks rather than materials prepared for artist’suse, there is a strong likelihood that they are examples ofthe triphenylmethane or ‘aniline’ dyes developed in the twodecades following Perkin’s introduction of mauve in 1856.By the 1880s, the range of aniline dyes was large with smallvariations in formulation producing new shades of red,orange, violet, blue and green.9 New dyes based on otherreactions were being developed and introduced but theywere, at the time, expensive and less widely available thananiline dyes for example, alizarin and other anthraquinonesafter 1870, Para Red (PR1) ca 1885, Acid Red 29 ca 1880.Carlyle10 charts the inclusion of ‘aniline’-based pigmentsin artist’s supplier’s catalogues with the majority notfeaturing until well after 1880; she also notes the numerouscontemporary comments on the fugitive nature, extremetinting strength and colour range of these materials. On thisbasis, a range of archival and modern aniline dyes wereprepared as stains for comparative purposes and examinedby Raman spectroscopy. All produced a similar stronglyfluorescent response. The range included known samplessuch as Methyl Violet 2B, generic mixtures such as GentianViolet and a range of historic commercial samples recordedas ‘aniline’ dyes in the collection of the Art Gallery of NewSouth Wales Conservation Department. Other materials, inaddition to traditional natural dyes and inorganic pigments,which are recorded in the literature as having been usedin red inks during the latter part of the 19th century, suchas eosin and Rhodamine B, were also examined. Unlike the‘anilines’ they tended to give recognisable and reproduciblespectra by Raman spectroscopy, albeit of variable quality.Other synthetic organic colourants close in date to thesketchbook for example anthraquinones and ˇ-naphtholshave previously been examined by us as pigments and thiswork has suggested that it is possible to get reasonablespectra from these materials by Raman Spectroscopy even indispersion.



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Figure 7. Raman spectrum from McRae blue identified as Prussian blue characterized by peak at 2150 cm�1.

FTIR microspectroscopy proved more successful. Eachof the raw materials examined produced distinct spectra;however, when allied to a paper support in the mannerof the sketchbook drawings, the spectrum obtained wasalmost wholly that derived from the paper. This resultwas repeated with the actual sketchbook inks with thespectrum again largely matching the unstained paper. Forthe sketchbook pink there was no difference in spectrabetween the stained and unstained paper, but for theviolet there was an additional band observed at 1600 cm�1

(Figs 8 and 9). This band was also observed in staining testswith a number of the known aniline dyes and equates tothe strongest band present in the raw dye spectra. Thestronger result for the McRae violet ink also indicates thegreater amount of this material, which could be observed,on the fibre during microscopic examination of singlepaper fibres. Even so, attempts at isolating the dye bythe introduction of solvents to the flattened sample wereunsuccessful.

The identification of inks compared with pigments onworks of art, at least with the equipment available tous, has been problematic. The lack of particulate matterwith characteristic optical features means that PLM haslittle to contribute for these materials above a very genericclassification. The intimate contact between the ink and thepaper and the lack of a discrete surface from which to samplealso makes isolating the ink from the support difficult. Lastly,the extremely strong staining power of many inks, especiallythe early anilines, means that even within brightly colouredareas, very little colouring material may actually be present.

Therefore, and depending on the nature of the work of art,sampling a sufficiently large area from which to extract auseful dye sample may be simply unfeasible. Although it ispossible to focus on paper fibres stained with ink using bothRaman and FTIR microscopes, it would appear, at least fromthis experience, that there may simply not be enough inkwithin the sample spot to dominate the resulting spectrum.

With regard to displaying the sketchbook, it will berecommended that those pages containing the suspect pinkand violet inks should have extremely limited exposureand that facsimiles be provided for scholarly research. Forexhibition purposes only those sketches executed in blackand/or blue will be designated as safe for use. Althoughwe could not prove that the pink and violet inks wereaniline dyes, it remains, from the associated evidence, astrong possibility that they are. Given that all aniline dyesare known to be fugitive, some more so than others but all toa greater extent than later alternatives, the risk of altering thepristine nature of this irreplaceable book is too great to take.11

CONCLUSION

For the conservator concerned with the identification ofmaterials, especially colourants, on objects in their care,Raman spectroscopy has many advantages when formulat-ing preventive or interventive strategies. It can act as a quickconfirmation for in-laboratory analysis by PLM and can inthe right circumstances be the sole tool needed. This is espe-cially so given the excellent resolution and minimal or nosample preparation needed for the Raman microscope. As


Raman microspectroscopy of works of art on paper

Plate 1. Leonetto Cappiello Nitrolian 1929 National Gallery of Australia, Canberra. (Offset lithograph).

Plate 2. Grace Cossington-Smith Portrait of Diddy c 1922National Gallery of Australia, Canberra. (Whole front).

Plate 3. Grace Cossington-Smith Portrait of Diddy c 1922National Gallery of Australia, Canberra. (Whole back showinglocalized discolouration).

Copyright 2004 John Wiley & Sons, Ltd. J. Raman Spectrosc. 2004; 35

D. Wise and A. Wise

Plate 4. Tommy McRae Sketchbook c 1880 National Gallery of Australia, Canberra. (Front cover).

Plate 5. Tommy McRae Sketchbook c 1880 National Gallery of Australia, Canberra. McRae sketches showing Aboriginal, Europeanand Chinese figures.

Copyright 2004 John Wiley & Sons, Ltd. J. Raman Spectrosc. 2004; 35


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Figure 8. FTIR spectra from Methyl Violet test: top, dye; middle, dyed paper; bottom, paper.

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Figure 9. FTIR spectra from McRae samples: purple dyed and undyed paper. Note additional band at 1600 cm�1.

we have found, a relatively basic facility is still capable ofproviding valuable information provided that its limitationsand restrictions are recognized and a flexible approach to thetask at hand is taken. In a cooperative inquiry, the data sup-plied by scientific analysis when combined with a knowledgeof working practices, available materials and art historicalresearch can provide practical results which have materialbenefits to the preservation and presentation of museum andart gallery collections.

AcknowledgementsThe authors thank Roger Heady of the Research School for BiologicalSciences, Australian National University, Canberra for access to andassistance with SEM analysis, the Conservation Department, ArtGallery of New South Wales, Sydney for access to FTIR microscopyfacilities, Mark Henshaw, Curator of International Prints, Drawingsand Printed Books, National Gallery of Australia, Canberra, DrVincent Otieno-Alego, Scientific Officer, Australian Federal PoliceForensics Service, Canberra and William Hamilton, National Galleryof Australia.



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Patton TC (ed). Wiley: New York, 1973; 497.2. Carlyle L. The Artist’s Assistant. Archetype: London, 2001; 510.3. Banik G, Stachelberger H, Waechter O. In Science and Technology

in the Service of Conservation, IIC, Brommelle NS, Smith P (eds).International Institute for Conservation London, 1982; 75.

4. Kuhn H. In Artist’s Pigments: a Handbook of Their Historyand Properties. Cambridge University Press: Cambridge, 1986;169.

5. Daniels V. Restaurator 1990; 11: 236.

6. Sayers A. Aboriginal Artists of the Nineteeth Century, OxfordUniversity Press, Australia, Melbourne, 1994; 28.

7. Sayers A. Aboriginal Artists of the Nineteeth Century, OxfordUniversity Press, Australia, Melbourne, 1994; 29.

8. Sistach MC, Ferrer N. Iron Gall ink corrosion in manuscripts in TheIron Gall Ink Meeting Postprints, University of Northumbria atNewcastle 2000; 73–81.

9. Arnold JB. In Pigment Handbook: Vol. 1. Properties and Economics,Patton TC (ed). Wiley: New York, 1973; 599.

10. Carlyle L. The Artist’s Assistant. Archetype: London, 2001; 158.11. de Tristan P. In IPC Conference Pre-prints, Eagan J (ed). IPC,

London, 1997; 107.


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