a million brown spots

A MILLION BROWN SPOTS AFTER CONSERVATION: UNTANGLING THE CAUSE-EFFECT CHAINMarieke KraanFrank J. LigterinkBirgit ReisslandBernadette van BeekBas van VelzenIneke JoostenPeter Hallebeek

This article is published on the ICN website with permission of ICON.

Edinburgh Conference Papers 2006, ed. S. Jaques (London: The Institute of Conservation, 2007), 59-66

©2007 Institute of Conservation

1 The owner of the artwork requested that theauthors not reveal the name of the artist normention the title of the artwork in publications,nor to contact the artist nor the art gallery wherethe work of art was sold. Thus, all illustrationsshow only details of the artwork.

A million brown spots after conservation: untanglingthe cause-effect chain

Marieke Kraan, Frank J. Ligterink*, Birgit Reissland,Bernadette van Beek, Bas van Velzen, Ineke Joosten andPeter Hallebeek

IntroductionIn 2003, discolouration of a large-format contemporary artwork on paper wastreated locally with hydrogen peroxide in a private paper conservation studio inThe Netherlands.1 The treatment result was considered to be satisfactory.Unexpectedly, three months later, a huge number of tiny brown spots emergedin the paper (Fig 1). These spots were rather disturbing and the artwork wasconsidered to be a total loss. During and shortly after the treatment, there hadbeen no indications that such a problematic side-effect would arise. The choice ofhydrogen peroxide as a bleaching agent and the application method used hadbeen based on sound results obtained throughout many years‘ experience of thistreatment strategy. Due to the fact that treatment with hydrogen peroxide iscommon in paper conservation, an explanation for the phenomenon wasconsidered essential to anticipate and prevent similar problems in the future.Moreover, clarification of the degradation mechanism was required in order toestablish a potential method for the removal of the spots.

History of the artworkThe artist had created the artwork in 1992, on the request of an art gallery inAmsterdam, using acrylic paint on paper. The paper support is white and isabout 0.4mm thick. Interestingly, the paper had been bought by the owner of theart gallery, in all probability at Peter van Ginkel Art Supplies in Amsterdam. Thedimension of the artwork is large, 149.5 � 246.0cm. Paper of this size is onlyavailable in a rolled format. The owner received a certificate from the galleryclaiming that the work of art is a painting in acrylic paint on Fabriano™ paper.Around the central painted area the artist left all the margins unpainted, theirwidth varying from 5cm to 20cm.The object had been hanging in the living room of the owner for a period of

about ten years. It had been mounted in a wooden frame, partly covering theouter edges of the paper. After some years, the paper had started to cockle(Fig 2) and it was for this reason that the owner had contacted a conservationworkshop. When the work of art was unframed it became evident that thecockling had been caused by the framing technique. The paper had been fixedonto Meranti plywood with metal staples and a white, paper-based gummedtape (Fig 3). The staples had punctured the paper all along the edges. Thoseedges that had been covered with the wooden frame remained white, while theunpainted paper areas, which had been exposed to daylight, displayedperceptible and relatively even discolouration (Fig 4). The conservatorssuggested that the paper gum-tape be removed, all the staple holes be repairedand the cockling be reduced. In response to an additional request by the owner,it was decided to reduce the local discolouration along the edges so that theartwork could be mounted in a new frame, which would allow the entire sheetto be visible after conservation.The conservation treatment was carried out in early 2003. On the recto all

unpainted paper areas were dry-cleaned with an eraser powder. The white papersupport of the gummed tape adhered to the edges of the work was removedmechanically after the local application of a 2% methyl cellulose gel to moistenthe tape adhesive. Remaining adhesive residues were removed with cottonswabs and demineralised water. The large central area of the artwork which was

59

Edinburgh Conference Papers 2006

Fig 1 Detail of the artwork showing the differentareas of discoloration that appeared afterhydrogen peroxide treatment.

Fig 2 Detail of the artwork showing cockling inthe margin area.

Kraan, Ligterink, Reissland, van Beek, van Velzen, Joosten and Hallebeek

2 The solution was prepared by addingdemineralised water to a concentrated solutionof reagent grade hydrogen peroxide (30% v/v;10ml:90ml). A few drops of ammonia (25% v/v)were applied to the solution to increase the pH topH7–8.

3 J. Hofenk de Graaff, Onderzoek CollageMatisse Documentatiemap 75/34, CentraalLaboratorium, Amsterdam, 1975. Unpublishedresearch report.

4 W.G.Th. Roelofs, J. Hofenk de Graaff, C.J. Fuitand P.J. Hallebeek, Onderzoek ter onder-steuning van de restauratie van Henri Matisse’sLa Perruche et la Sirène, Documentatiemap 96/21,Centraal Laboratorium, Amsterdam 1996.Unpublished research report.

5 P. Vermeulen, ‘An Investigation into theDiscolouration of the Background Paper ofMatisse’s La Perruche et la Sirène’, The PaperConservator 21 (1997): 15–25.

covered with thick layers of acrylic paint precluded an immersion treatment.Moreover, in view of the large size of the object, it was decided to treat thediscolouration locally.First, all discoloured areas were wetted from the recto with demineralised

water using an airbrush. The painted areas remained untreated and were fullycovered with blotting paper throughout the treatment. In some areas thecoverage extended into some unpainted areas due to the irregular outline of thepaint. The moisture was subsequently blotted off, with the aim of extractingwater soluble coloured degradation products. This initial washing procedurewas not successful, as the discolouration did not disappear. As a consequence,the treatment was extended by applying a diluted solution of, an oxidizingbleach, hydrogen peroxide in water (3%) to minimise the discolouration.2 Thehydrogen peroxide solution was applied locally with an airbrush on thediscoloured areas (Fig 5 (1)). The use of an airbrush achieved a subtle continuoustransition between discoloured and non-discoloured areas. After the hydrogenperoxide treatment the object was left to air dry overnight.The next morning the discolouration had lessened but not sufficiently.

Therefore, it was decided to repeat the hydrogen peroxide treatment. Directlyafter the airbrush application, while the object was still moist, hydrogen peroxidewas locally brushed along the most discoloured areas to increase the bleachingeffect (Fig 5 (2)). The applied quantity of applied solution might have variedlocally in these areas. Again, the object was air dried. As a next step, the objectwas sprayed several times on the recto using an airbrush with demineralisedwater, in an attempt to remove any remaining bleach residues from the paper.Surplus liquid was removed using blotting paper. The discolouration was notperceivable after the treatment. The staple holes and small tears were filled fromthe recto with cotton linters pulp. They were supported on the verso with KōzoNo. 3 Japanese paper and wheat starch paste. Finally, the unpainted edges wereslightly flattened by spraying the paper with demineralised water and allowingthem to dry between thick blotting paper under light weight. After treatment, theartwork was mounted in a new frame by a picture framer, leaving the outeredges of the artwork visible. The result was evaluated to be satisfactory. Theartwork was placed in the living room of the owner.Within a period of three months, thousands of tiny brown spots had appeared

in the treated areas. The owner contacted the conservators again.

Local discolouration in paperLocal discolouration in paper artworks is usually considered to be disturbing,whether it is in the form of spots or more general, uneven areas, and as such isa reoccurring topic in the field of paper conservation research. In some cases,local discolouration can be attributed to specific contamination. However, it isoften difficult to explain specific causes for certain discolouration patterns suchas foxing or mat burn. Until now there has been no published classification witha generally accepted terminology to describe discolouration patterns in paper.Although the occurrence of local discolouration in paper is a general issue thereare only a few documented cases to which to refer. Some of those cases showedcertain similarities with the type of scattered, local spots of discolouration thatevolved in the artefact of this study.1 La Perruche et la Sirène by Henri MatisseA well known example, for a relatively fast progressing, inhomogeneous

discolouration in paper, is the collage La Perruche et la Sirène by Henri Matisse,owned by the Stedelijk Museum in Amsterdam. The large-format papersupport for this collage (340 � 775cm) had to be replaced three times, becauseafter a period of seven years and another period of four years, localdiscolouration became apparent again and again. Despite serious researchattempts no final conclusion could be drawn. None of the suggested theoriescould explain the typical semi-random patterns that occurred in thebackground paper.3, 4, 5 The large format of the paper, the relatively fastevolving areas of discolouration as well as their random nature showed

60

paper tapestaple

frame

artwork

glass

meranti plywood

2

3

4

5

1

1

23

Fig 5 Schematic drawing of a detail of theartwork, illustrating the areas treated withhydrogen-peroxide solution: (1) airbrushapplication (2) brush application (3) untreated.

Fig 4 Schematic drawing of a detail of theartwork before conservation, illustrating the (1)painted area (2) unpainted area (3) discolouredarea (4) area covered by frame and (5) areacovered with paper tape.

Fig 3 Cross section diagram of the originalframe and mount.

Amillion brown spots after conservation: untangling the cause-effect chain

6 B. Reissland, ‘Media problems: Two CaseStudies’, Papier Conserveerend Nederland (TheHague, The Netherlands, 2001) unpublished.

7 M. Hey, ‘Paper Bleaching: Its simpleChemistry and Working Procedures’, The PaperConservator 2 (1977): 10–23.

8 J.G. Neevel and B. Reissland,‘Bathophenathroline Indicator Paper,Development of a New Test for Iron Ions’,PapierRestaurierung Mitteilungen der IADA, 6No1 (2005): 28–36.

similarities with the art work discussed here. Appearance, shape anddistribution of the discolouration, however, did not correspond.2 A nineteenth-century watercolourA second case of fast appearing paper discolouration was reported for a

hydrogen peroxide treatment of a watercolour in pen and brown ink carried outin 1995.6 The paper support showed intense discoloured foxing stains beforeconservation, especially in the sky area, that disturbed the impression of theimage. Due to the presence of fugitive watercolour, only restricted aqueoustreatment was feasible. It was decided to bleach the foxing stains with anaqueous solution of hydrogen peroxide, applied locally with an airbrush. Toremove soluble, discoloured products from the paper, wet blotting paper hadbeen used. Approximately six months after completion of the treatment, intensebrown paper discolouration appeared on the verso. Examination under amicroscope revealed that colour accents drawn in brown ink were present on therecto exactly at those places where the discolouration occurred on the verso side.Testing with a bathophenanthroline indicator for iron(II) ions indicated that theink contained iron ions and probably was an iron-gall ink. Hydrogen peroxide isa strong oxidizing agent that, in combination with the iron(II) ions present in theink, had caused the undesirable catalytic oxidation of the cellulose.7 Theresulting cellulose-degradation products are likely to have caused the paperdiscolouration over time. The hydrogen peroxide treatment, the applicationmethod using an airbrush, extraction of soluble products with wet blotting paperand the short period of time until the paper discolouration appeared, allcorrelated with the treatment procedure carried out on the artwork in this study.Summarising, it can be stated that the development of brown spots or

discolouration in paper often remains difficult to explain, and nearly impossibleto predict. Important factors that play a role in the development of these type ofbrown spots are the materials and processes used in: the manufacture of thepaper, the creation of the art work, mounting, storage and conservation. The aimof this research was to deduce which combination of factors caused theappearance of the brown spots of discolouration in the present case.

Experimental1 Visual examinationThe recto and verso of the artefact were examined visually under both

daylight and artificial light, as well as using a UV lamp, raking and transmittedlight. Details were examined with a pocket microscope (25x and 50x) and astereomicroscope present in the conservation laboratory. The primary supportwas compared to samples of all Fabriano™ papers that can currently be obtainedin The Netherlands in roll format, supplied by the Dutch representative ofFabriano™ (Colart B.V., Capelle aan de IJssel). According to the representative,the current range of Fabriano™ papers coincides with those sold in the 1990s.2 Bathophenanthroline-indicator paper for iron(II) ionsThe presence of iron(II) ions in the paper and the discoloured spots was

determined by carrying out a non-bleeding contact test with a moistenedbathophenanthroline-indicator paper.8

3 Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS)Paper samples from spot areas were taken with a scalpel and a pocket

microscope from the surface of the verso of the artwork. The samples wereanalysed with Energy Dispersive Spectroscopy (EDS, Thermo NoranInstruments, model: Vantage) in a JEOL 5910LV Scanning Electron Microscope(SEM) in low vacuum (30 Pa), accelerating voltage 15–20 kV. Both backscatteredelectron images and secondary electron images were taken.4 X-ray diffraction (XRD)In addition to the SEM/EDS analysis, some samples were investigated with

the help of x-ray diffraction (GADDS micro diffractometer) to determine thecrystalline nature of the substances present.

61


Results1 Visual examinationThe visual examination primarily focussed on paper discolouration patterns. A

number of predominant features were distinguished (Fig 6): a homogeneousdiscolouration, local brown spots, tide lines and patterns appearing only under UV.The homogeneous paper discolouration that had originally been present

before treatment had now re-appeared with even more intensity. In comparisonto the non-discoloured paper these areas showed a reduced fluorescence underUV illumination. In addition to this, a distribution of many small, brown spotshad formed. Nearly all treated areas had these spots, except for the margin areaswhich had been covered with gummed paper tape. When looking undertransmitted light, additional spots were visible underneath the paper surface, inthe core of the paper. On the verso of the artwork the spots were concentrated ina band which was about 1cm wide, parallel to the edges of the object. In somelocations, the band broadened to a few centimetres (Fig 7). This band coincidedwith the area where the hydrogen peroxide had been applied with a brush. Thespots were circular, with a diameter of between 0mm and 2mm. The colour of thespots varied from faint to strong brown. Within some spots the colourdistribution appeared homogeneous. Other spots showed a dark brown centresurrounded by a lighter area. The outlines of the spots varied from appearingvery distinct to very diffuse. Under UV illumination the spots appeared darkeragainst their background. On the verso of the treated area the spots were smaller,more distinctively bordered and more intensely coloured than on the recto.Another type of local discolouration consisted of slightly visible tide lines.Examination under UV illumination revealed fluorescent patterns similar towood grain in appearance on the verso that were not visible in daylight.Apart from these areas of discolouration the following other features were

noticed. In the untreated areas, no brown spots were observed with the nakedeye (Fig 8). However, under a microscope (magnification 25x) a sparsedistribution of minute black-coloured spots could be seen. Neither the thickness,colour nor texture of available Fabriano™ papers resembled those of the paperof the artwork. Contrary to the artwork paper, all Fabriano™ papers sold in rollformat contain press marks along the roll edge. It is not possible that the artisthad cut off these edge marks. None of the Fabriano™ papers examined exceededa width of 150cm, including the two press mark edges with a width of 1.5cmeach. Cutting off these Fabriano™ press-marks would have resulted in amaximum width of 147cm, the object however measures 149.5cm. Along the

62

Fig 8 Detail of the artwork showing absence ofspots in an untreated area (upper part) andpresence of spots in a treated area (lower part),recto.

Fig 7 Detail of the artwork showing a band of spots, verso.Fig 6 Detail of the artwork showing homogeneous discolouration, spotsand tide lines, recto.


9 W.R. Willets, A.M. Brooks, W.L. Craig, G.Haywood, C.G. Albert, J.W. Kenney, P.W. Leppla,V.A. Belcher, R.S. McClellan and F.H. Denham,Tappi, Paper Loading Materials, Tappi MonographSeries No. 19 (New York: Technical Associationof the Pulp and Paper Industry, 1958) 69.

10 The name chlorite is derived from the Greekword chloros, meaning ‘green’, in reference to itscolour, not to chlorine as a compound. Inliterature on fillers, the minerals from the chloritegroup are often referred to as being ‘chlorite’with no further specification.

11 C.A.J. Appelo and D. Postma, Geochemistry,Groundwater and Pollution, 2nd edition (Leiden:A.A. Balkema Publishers, 2005).

edges, with a width of approximately 1cm, differences in gloss was observed.2 Bathophenanthroline-indicator paper for iron(II) ionsAt seven locations, four on the recto and three on the verso of treated and

untreated areas, the non-bleeding iron test was conducted. All brown and blackspots showed a positive reaction.3 Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS)When samples were taken for analysis, it became clear that the paper within the

brown spots had severely degraded. When cut, the central parts of sampled spotsfell out, leaving holes in the samples. Samples with smaller spots did not have thisproblem to the same extent. The backscattered image of the paper surface showssuch a hole within a distribution of fibres and particles (Fig 9). EDS-analysisindicated an increased iron concentration around the edges of the holes (Fig 10).For those two samples that remained intact during sampling, local increasedconcentrations of iron and sulphur were determined with EDS-analysis thatcorrelated to the brown spots of discolouration (Fig 11). Closer investigation of thecore areas with the highest iron concentration revealed the presence of a centralparticle containing iron and sulphur with a size of approximately 10–20µm(Fig 12). One particle appeared as a single, mineral-like fragment, while the otherhad an amorphous conglomerate structure. The majority of particles visible in theSEM images showed a plate-like particle shape and contained magnesium andsilica. Their particle size typically ranged between 1–10µm.4 X-ray diffraction (XRD)One of the samples with an increased iron-sulphur concentration was

analysed using x-ray diffraction. The diameter of the analysed area was ca.800µm. Comparison of the diffraction data with those of the reference XRD-database matched 3 crystalline substances: clinochlore, talc and iron sulphate.

DiscussionApplying the results of our research to the condition of the artwork and itshistory allowed us to develop a better understanding of the cause-effect chainthat finally lead to the unexpected outcome of the conservation treatment.1 Paper productionOur starting point was the manufacture of the primary support. Although a

certificate stating that the artwork was made on paper produced by Fabriano™(Italy) appeared to have been issued by the gallery that sold the artwork, this factcould not be confirmed. It is highly unlikely that a Fabriano™ paper was used. Itremains unclear who actually produced the paper. Within the paper, threematerials were identified with XRD: talc, chlinochlore and iron sulphate. The firsttwo substances are commonly used as fillers in the paper industry.9 Talc(Mg3Si4O10(OH)2) is a mineral composed of magnesium silicate hydroxide. Itschemical inertness and its excellent white colour make it particularly suitable as afiller material for paper to improve gloss, opacity, brightness and ink retention.Clinochlore (Mg,Fe2+)5Al(Si3Al)O10(OH)8 contains iron and belongs to the chloritegroup of clay minerals.10 Mineral clay materials are cheap and widely used in thepaper industry. They improve brightness and gloss, and increase the opacity andthe printability of paper. The plate-like particle shape of both minerals is consistentwith the SEM imaging. The third substance identified is iron sulphate. Its presencecan be understood in relation to the established presence of particles with a highiron and sulphur concentration in the paper of the artwork. Chlinochlore naturallyoccurs together with magnetite (Fe2+ Fe3+

2 O4), pyrite (FeS) and other ironsulphides. Although materials destined for use as a filler in papermaking need tobe free from contamination and require the removal of impurities, this rule appearsnot to have been applied and a contaminatedmaterial was used. Iron sulphides arechemically unstable substances when exposed to oxidizing environments. Underthe influence of water and oxygen they are transformed in complex reactionsystems to iron(II) sulphate and sulphuric acid,11 a particularly detrimentalcombination to organic materials such as cellulose. It is probable that the paperoriginally contained a uniform distribution of minute, to the naked eye invisible,iron sulphide particles which were transformed into iron sulphate.

63

Fig 9 Backscattered electron image of a sampleof spot area with hole.

Fig 10 Elemental map, superimposed on abackscattered electron image. The edges of thehole show a higher iron concentration (in red).


12 The discolourations were removed using thefollowing procedure: Initial thorough blotterwashing (distilled water, application from rectoand verso with airbrush), subsequent applicationof sodium borohydride in concentrations of0.1%, 0.4% and 0.2% (dissolved in water with theaddition of ethanol to improve the penetration),followed by thorough blotter washing (distilledwater) and a deacidification treatment applyinga saturated solution of calcium bicarbonate.Finally, the treated areas were surface sized withgelatine (0.5% in water, application withairbrush).

2 MountingThe presence of fluorescing wood-grain-like patterns on the recto of the paper

and the observed gloss along the edges were consistent with the information onthe mounting technique.3 StorageThe homogeneous discolouration appeared during the time that the object

was exhibited in the owners’ home. Whilst framed, different parts of the artworkhad been exposed to different levels of light as some areas had been covered byeither the frame or paint layers. Those areas of the paper that had had less lightexposure showed a higher level of fluorescence on the verso. It is likely that anoptical brightener present in the paper had degraded under the influence of UVand light in the exposed areas, causing the paper to appear more yellow. It is alsolikely that the temperature and humidity conditions to which the paper had beenexposed varied locally in the frame. Which factor finally caused thediscolouration cannot, however, be determined.4 ConservationIt is apparent that the hydrogen peroxide treatment triggered the occurrence

of the brown spots. Most likely the introduction of an oxidizing agent led to thelocal transformation of the iron sulphide particles to iron(II) sulphate throughoutthe treated areas. The brush application of an additional treatment solution hadcaused the spots to appear on the verso also. The applied blotting procedure,intended to remove residues of the bleaching agent, has proven to be insufficient.

ConclusionsThe occurrence of the disturbing brown spots in the artwork can be understoodas being the result of a combination of mainly two factors. The paper used for theartwork is of poor quality. In combination with the use of an oxidizing treatmentagent and the, probably, insufficient washing procedure, large amounts ofmicroscopic particles of iron sulphide, present in the paper, transformed into ironsulphate, a detrimental substance for organic materials. However, in thepresence of atmospheric oxygen these iron sulphides are chemically unstable,and can have been expected, in the long run to have caused discolouration evenwithout the addition of any treatment agent.Recommendations in paper conservation literature concerning the use of

hydrogen peroxide as a bleaching agent are ambiguous. Although variousauthors claim that hydrogen peroxide is a relatively mild and well controllablebleaching agent, it is also known that hydrogen peroxide in combination withtraces of iron and other transition metals can cause problems. Until recentlyhowever, no suitable test method has been available to conservators to test forthe presence of iron. Even so, in the current case with iron-containing particlesembedded in the paper, one has to doubt if their presence could have beendetected beforehand. For future treatments we strongly recommend pre-testingobjects for the presence of metal contamination, using a microscope, UVillumination and specific indicator tests.The occurrence of undesired side-effects as a result of a conservation

treatment is rather frustrating for all parties involved. It should be stressed thatrisk can never be fully eliminated from the conservation profession. It is the taskof conservators and conservation scientists to identify and mitigate significantrisks by sharing knowledge and experience amongst themselves, and also tocommunicate these risks in any decision making processes with owners andcurators.

EpilogueFollowing this research the artwork received another conservation treatment.The spots have been removed.12 The object has returned to its original location inthe owners’ house. Although the current result is felt to be acceptable it isrecognized that the object remains unstable and is likely to meet moregenerations of paper conservators on its path.

64

Fig 12 Backscattered electron image from centreof Fig 11. Within the high iron concentration aparticle could be observed containing theelements iron, sulphur and oxygen.

Fig 11 Elemental map, superimposed on abackscattered electron image of a sample takenfrom a brown spot. At the centre and left sidebelow, the iron concentrations are highest (ironin red).


AcknowledgementsWe would like to thank the following conservators, chemists and otherspecialists for their valuable contributions: Nico Lingbeek (Lingbeekpapierrestauratie, NL), Francien van Daalen (van Daalen Papierrestauratie,NL), Gerhard Banik (Staatliche Akademie der Bildenden Künste Stuttgart,D), Andrea Pataki (Staatliche Akademie der Bildenden Künste Stuttgart, D),Michaela Ritter (Masson Pictet Boissonnas Gemälde-undGraphikrestaurierungen AG, CH), André van Oort (Haarlem, NL), BobHildering (Apeldoorn, NL), Linda Roundhill (Arts and AntiquitiesConservation, Woodinville, USA), Leslie Kruth (Stanford UniversityLibrary, USA), Lenkat & Madhari (India), John Havermans (TNO, Delft,NL), Hiromi Tanimura (Japan), Niccolo Caldararo (San Francisco StateUniversity, USA), Sylvia Rodgers Albro (Library of Congress, USA), HanNeevel (ICN Amsterdam, NL).Furthermore, we would like to thank Piet van Nassau (Colart B.V., NL)

and the colleagues of Van Ginkel Kunstenaarsbenodigdheden (NL) forsharing information on the subject of the Fabriano™ papers as well as forthe contribution of paper samples for further analysis.

SummaryA large-format contemporary artwork was locally treated with hydrogenperoxide to remove paper discoloration. Three months after treatment alarge number of small brown spots appeared in the artwork.In order to understand the phenomenon and prevent similar problems in

the future, the artwork was examined visually and analysed withbathophenanthroline iron-indicator paper, with energy dispersivespectroscopy (EDS, Thermo Noran) in a JEOL 5910LV Scanning ElectronMicroscope (SEM) and x-ray diffraction analysis (XRD, GADDS microdiffractometer). The research showed that the paper support wascontaminated with microscopically small particles (~10 micrometers)containing iron and sulphur. The source of this impurity was most likely theclay clinochlore that was introduced as filler during paper production. Theunlucky combination of the presence of these particles and the hydrogenperoxide treatment caused an undesired catalytic oxidation of the cellulosethat finally resulted in the formation of the brown spots of discolouration inthe treated area in such a short period.It is concluded that the problem could not have been anticipated using

test methods currently available to paper conservators. We hope that thepresent case will raise the awareness amongst conservators and will enablethem to inform their clients more precisely about the potential risksassociated with hydrogen peroxide treatments.

RésuméUne oeuvre d’art contemporain de grand format a été traitée localementavec du peroxyde d’hydrogène afin d’enlever le jaunissement du papier.Trois mois après le traitement, un grand nombre de taches brunes sontapparues dans l’œuvre.Afin de comprendre le phénomène et pour éviter des problèmes

similaires à l’avenir, l’œuvre d’art a été examinée visuellement et analyséeavec un papier indicateur de la présence de fer à base debathophénanthroline, par spectroscopie à dispersion en énergie (EDS,Thermo Noran) dans un microscope électronique à balayage (SEM) JEOL5910LV et par diffractométrie de rayons x (XRD, micro diffractomètreGADDS). La recherche a montré que le support en papier était contaminéavec des particules microscopiques (~10 micromètres) contenant du fer etdu soufre Il est plus que probable que la source de ces impuretés est leclinochlore de l’argile ajouté pendant la fabrication du papier commecharge. La combinaison malencontreuse des ces particules et le traitementavec le peroxyde d’hydrogène a causé une oxydation catalytique nondésirée et a finalement entraîné la formation de taches de couleur brunedans la zone traitée dans un délai aussi court.On a conclu que ce problème n’était pas prévisible par les tests

habituellement utilisés par les restaurateurs de papier. Nous espérons que

ce cas sensibilisera les restaurateurs et leur permettra d’informer plusprécisément leurs clients sur les risques potentiels liés aux traitements avecdu peroxyde d’hydrogène.

ZusammenfassungEin großformatiges, zeitgenössisches Kunstwerk wurde lokal mitWasserstoffperoxid gebleicht, um Verfärbungen im Papier zu entfernen.Drei Monate nach dieser Behandlung wurde eine Vielzahl kleiner braunerFlecken auf dem Werk sichtbar.Um dieses Phänomen zu verstehen und um ähnliche Probleme in der

Zukunft zu vermeiden, wurde das Werk visuell begutachtet und mitBathophenathrolin – Eisenindikatorpapier, EnergiedispersiverRöntgenspektroskopie (EDS, Thermo Noran) in einem Rasterelektronen-mikroskop (SEM, JEOL 5910LV) sowie mit Röntgendiffraktion (XRD,GADDS Mikrodiffraktometer) analysiert. Die Untersuchungen zeigten, daßdas Papier mit mikroskopisch kleinen Partikeln (< 10 Mikrometer)kontaminiert war, die Eisen und Schwefel enthielten. Ursprung dieserVerunreinigung war höchstwahrscheinlich der Ton ‘Clinochlore‘, der alsFüllstoff bei der Papierproduktion eingesetzt worden war. Dasunglückliche Zusammenspiel der Anwesenheit der Füllstoffpartikel undder Wasserstoffperoxid – Behandlung verursachte ungewollt diekatalytische Oxidation der Zellulose, was letztendlich zur Bildung derbraunen Verfärbungen in den behandelten Bereichen führte.Eine wichtige Schlussfolgerung besteht darin, daß die Restauratoren das

Problem mit den ihnen derzeit zur Verfügung stehenden Testmethodennicht vorhersehen konnten. Wir hoffen, daß dieser Fall Restauratorenalarmiert und es ihnen ermöglicht, ihre Auftraggeber in Zukunftumfassender über die potentiellen Risiken einer Wasserstoffperoxid –Behandlung zu informieren.

ResumenUna obra contemporánea de gran formato fue localmente tratada conperóxido de hidrógeno para eliminar descoloración en el papel. Tres mesesdespués del tratamiento aparecieron sobre la obra numerosas manchitasmarrones.Con el fín de entender el fenómeno y de preveer similares problemas en

el futuro, la obra fue visualmente examinada y analizada con papelindicador del hierro con fenantroline, con espectroscopía de energíadispersa (EDS, Thermo Noran) en un JEOL 5910LV microscopía electrónicade barrido (SEM) y bajo análisis de difracción por rayos X (XRD, GADDSmicro difractómetro). La investigación mostró que el papel de soporteestaba contaminado con partículas microscópicas (~10 micrones) quecontenían hierro y sulfuro. El orígen de estas impurezas era, muyprobablemente, la cal de clinocloro que fue introducida como rellenodurante la producción del papel. La desafortunada combinación de estaspartículas y el tratamiento de peróxido de hidrógeno causó una indeseableoxidación catalítica de la celulosa que finalmente provocó, en tan cortotiempo, la formación de las descoloridas manchas marrones en el áreatratada.Se concluyó que el problema no podría haber sido prevenido con los

habituales métodos de testar papel usados por los conservadores de papel.Esperamos que el presente caso alerte a los conservadores y que les permitainformar con precisión a sus clientes sobre los potenciales riesgos asociadosa los tratamientos de peróxido de hidrógeno.

BiographiesMarieke Kraan and Bernadette van Beek jointly run the private paperconservation studio Atelier KOP in Arnhem.

Frank Ligterink, Birgit Reissland, Dr. Ineke Joosten, Peter Hallebeek areconservation scientists at the Research Department of the NetherlandsInstitute for Cultural Heritage (ICN). Bas van Velzen is head of the Bookand Paper Conservation Training Program at the ICN.

65

Materials and suppliersAmmonia: 25%, chemical pure:InterchemaRozenburgThe Netherlands

Demineralized water:Tendo’sTenden BVRotterdamThe Netherlands

Eraser Powder: Akablast; Cotton linters, white;Filter paper thin (120gm-2) and thick (300gm-2):Jansen Wijsmuller & BeunsWormerThe Netherlands

Ethanol Alcohol ketonatus 96% v/v (ketonatedethyl alcohol):Fagron Farmaceuticals BVNieuwekerk aan de IJsselThe Netherlands

Gelatine powder:Genfarma BCSterrebaan 143606 EB MaarssenThe Netherlands

Hydrogen peroxide 30%, medical pure,stabilized:Merck KGaAFrankfurter Strasse 25064293 DarmstadtGermany

Japanese paper: Kōzo No. 3:Private supplier, Japan

Methyl cellulose, Methylcellulosum, 4000 m.Pa.s:OPG FarmaBufa BVUitgeestThe Netherlands

Sodium borohydride, powder, 98+%, nitrogenflushed:Acros Organicshttp://www.acros.com

Wheat starch powder, Tritici amylum:Genfarma BVZaandamThe Netherlands

Kraan, Ligterink, Reissland, van Beek, van Velzen, Joosten and Hallebeek66

Contact addressesMarieke Kraan and Bernadette van Beek:Atelier KOP (Kunst Op Papier)Postbus 1221NL-6801 BE ArnhemThe Netherlands

Frank Ligterink, Birgit Reissland, Dr. Ineke Joosten,Peter Hallebeek and Bas van Velzen:Netherlands Institute for Cultural Heritage (ICN)Conservation Science DepartmentResearch/Training and EducationGabriël Metsustraat 8NL-1071 EAAmsterdamThe Netherlandsemail: [email protected]

*author to whom correspondence should be addressed

a million brown spots

Technology