POSTPRINTS_RECH_4_CROATIA_4_TH_INTERNATI

Nome artigo 51 of cracks using a small pointed brush. An attempt was made to imitate the variety of tones, forms and orientation of the lines present in the original craquelure. This helped to achieve the persuasiveness and vividness of the entire reconstructed surface, but most importantly, it decreased the brightness of the tiles and flattened the affected areas to the desired level (figure 6). Clearly, this kind of approach required a lot of preparation and thus the retouching could not be executed rapidly. The splatter technique was used in the final step as well - pure white paint was carefully splattered onto the reconstructed tiles giving the surface a certain antique character (figure 7). It is important to note that during the reconstruction of the tiled floor, the applied layers of paint (especially those from the splatter technique) were not piled up, but rather evenly Figure 7 • Detail of the painting after retouching. Photo © Ljubo Gamulin

52 Katarina Alamat Kusjanović | Sandra Šustić distributed on the surfaces. In this manner the final tone contained the information of all the previous layers which contributed to the effect of high luminosity. It was very interesting to observe how the network of artificial cracks has created a darker tone of the pavement but at the same time it didn’t corrupt the hue and the intensity of the colour. This helped to “push back“the lacunae and assimilate them into the original paint layer as much as possible. 3. RESULTS AND DISCUSSION 3.1. Reconstruction as a critical interpretation The integration of major compositional losses is considered as one of the fundamental issues of the restoration process, highly dependent on the type, placement and function of an object. Due to the liturgical importance of the All Saints painting, the complex damage of the lower part of the composition corrupted the meaning of the artwork and degraded its value. Thus the executed reconstruction was a preferable part of the intervention course. According to Mora, Mora and Philippot, the reconstruction is aesthetically justifiable as long as it aims in making it easier to see the potential formal unity of the work - the operation should stop where hypothesis begins. [10] The concept for the reconstruction of the lower part of the All Saints was strongly supported by the evidence from the preserved paint layer. As explained in the previous chapter, the hue reconstruction of the tiles was a straightforward task, while the artist’s use of linear perspective enabled an accurate arrangement of the missing form. 3.2. The degree of finishing Both invisible and visible inpainting techniques were at times subjected to criticism. [11, 12] According to Brajer differences of opinion seem to occur when we enter into the domain of aesthetics and the choices we made can have a profound effect on the perception of authenticity of a given object. [13]The high degree of finishing shown in the retouching phase of the All Saints project depended primarily on the style and physical characteristics of the painting. In order to further elaborate this argument it is necessary to recall the broad view of Philippot: “If the rupture caused in a medieval fresco can often be filed in by a simple hue – as long as its value and density places it as the proper constructive level – the importance of a detail, finish, and enamel-like appearance to create the atmosphere proper to a Flemish primitive painting will demand for the realization of an equivalent integration, an infinitely more elaborate retouching.“ [14] Of course, Santa Croce’s painting style is hardly comparable to Flemish primitives, but the delicate texture of the cracked paint layer and consequent luminosity, required an outstanding precision in retouching and the use of the finest materials in order to achieve the credibility of the reconstructed area. One of the basic tenets of retouching is that it must be performed with no

“All saints are in the detail“: retouching a painting by girolamo da Santa Croce 53 attempt to misrepresent the artist’s intent in respect to the physical characteristics of the painting. [15] As previously elaborated, the formation of the highly pronounced craquelure of the All Saints paint layer has compromised the intention of the artist by flattening and darkening the image. Thus, with respect to the artist intention, the alternative approach could have been to selectively reduce the visual disruption of the cracks on the preserved tiles and exclude the emulation of the craquelure on the reconstructed area. However, the concealment of the authentic craquelure could have resulted in misrepresentation of the genuine condition of the paint layer and the actual age of the painting. 4. CONCLUSION One of the conservator’s essential task is to acknowledge the artist’s intentions with respect to the overall condition of the artwork. However, the complexity of the All Saints retouching demonstrates that achieving a balance between the artist’s intentions and the condition of the painting is not an easy task. The challenge was imposed by the specific physical characteristics of the paint layer – such as the extremely subtle texture, the luminosity effect and the highly pronounced agerelated craquelure that the panel has acquired through time. This called for an infinitely more elaborate retouching, as described by Philippot. In order to mimic the unique look of a dense textured surface, a careful selection of the retouching tools, materials and techniques needed to be made. Besides the use of glazes and splatter techniques to produce smooth transition of tones, a crucial factor in obtaining the desired tonality was the rendering of the artificial craquelure. This helped to harmonize the retouching with the condition of the painting as a whole. REFERENCES [1] FISKOVIĆ, Cvito - Neobjavljena djela Girolama i Francesca da Santa Croce na Visu, Lopudu i Korčuli. Peristil. Vol. 6–7 (1963), pp. 57–66. [2] ŠUSTIĆ, Sandra - Djelovanje Cvite Fiskovića na zaštiti i restauraciji povijesnog slikarstva i skulpture na hrvatskoj obali. Unpublished PhD dissertation: University of Figure 8 • Detail of the floor before and after the retouching. Photo © Vlaho Pustić, Ljubo Gamulin

54 Katarina Alamat Kusjanović | Sandra Šustić Zagreb, 2016., p. 308-309. [3] BOMFORD, David - Picture cleaning: positivism and metaphysics. In: HILL STONER, Joyce; RUSHFIELD, Rebecca, eds. - Conservation of Easel Paintings. London and New York: Routlege, 2013, pp. 481-491, p. 486. [4] BUCKLOW, Spike - The description of craquelure patterns, Studies in Conservation. Vol. 42, (1997), pp. 129–140. [5] ABAS, Fazly Salleh - Analysis of Craquelure Patterns for Content-Based Retrieval. Unpublished thesis submitted in partial fulfillment for the degree of Doctor of Philosophy: University of Southampton, 2004. pp. 15-18. [6] Bucklow, Spike - The Effect of Craquelure on the Perception of the Pictorial Image, Zeitschrift für Kunsttechnologie und Konservierung, Vol. 8, n.º 1, (1994), pp. 104-111. [7] Bucklow, Spike - The Effect of Cracks on the Perception of Paintings. Official web site of the Hamilton Kerr Institute. Available at: https:// www.hki.fitzmuseum.cam.ac.uk/projects/ cracks [10 October 2017]. [8] MOHEN, J. P., et al. - Mona Lisa, Inside the painting, Harry N. Abrams inc, New York, 2006. [9] ALBERTI, L.B. - On Painting and on Sculpture. Penguin Classics, London Greenwood Press,1991. [10] MORA, Paolo et al. – Problems of presentation. In: STANLEY PRICE, Nicholas et al., eds. - Historical and Philosophical Issues in the Conservation of Cultural Heritage. Los Angeles: Getty Publications, 1996, pp. 343–354, p. 345. [11] BRANDI, Cesare - Il fondamento teorico del restauro, Bollettiono dell’ instituto Centrale del Restauro. 1, (1950), pp. 5–12. [12] SECCO-SUARDO, Giovanni - The idea of the perfect restorer. In: BOMFORD David and LEONARD Mark, eds. - Issues in the Conservation of Paintings. Los Angeles: Getty Conservation Institute. pp. 331–8 [A translation of the 1866 text.] [13] BRAJER, Isabelle - Authenticity and restoration of wall paintings: issues of truth and beauty. In: HERMENS E. and FISKE T. eds. - Art, Conservation and Authenticities: Material, Concept, Context. London: Archetype Publications, 2009, pp. 22-32. [14] PHILIPPOT, A.; PHILIPPOT P. – The Problem of Integration of Lacunae in the Restoration of Paintings. In: STANLEY PRICE, Nicholas et al., eds. - Historical and Philosophical Issues in the Conservation of Cultural Heritage. Los Angeles: Getty Publications, 1996, pp. 335- 342, p. 337. [15] DIGNEY-PEER, Shawn - The imitative retouching of easel paintings. In: HILL STONER, Joyce; RUSHFIELD, Rebecca, eds. - Conservation of Easel Paintings. London and New York: Routlege, 2013, pp. 607-635, p. 608, 612.

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ABSTRACT Powdered micro-cellulose is commonly used in the paper conservation lab for filling small losses, concealing stains and treating other damages on paper. Its neutral pH, general chemical stability and low toxicity, makes powdered cellulose a very reliable and compatible material, and also proved to be suitable for conservation purposes, like infilling and colour matching of the paper support. However, the ageing of this pure powdered cellulose, especially when modified by toasting to adjust its colour, is unknown. Obviously, this toasting gives room for some chemical changes, that’s why conservators should look for possible caveats of its use. To THE SUITABILITY OF POWDERED MICRO-CELLULOSE FOR ITS USE IN PAPER CONSERVATION Rita Udina (1) | Amparo Escolano (2) 1 Rita Udina - Paper & Books Conservation; C. Sant Pere, 24; Premià de Mar – 08330, SPAIN; [email protected] 2 South Florida Art Conservation; 500 Palm St. Ste 35, West Palm Beach, Florida 33401, USA; [email protected]

1. INTRODUCTION Cellulose powder is being widely used in paper conservation to conceal stains, fill small losses or gaps in tears, diminish abrasions, and repair damages created by silverfish or tape [1][2][3]. Since micro-cellulose is a very similar material to paper, the visual results obtained using it are very pleasant. In order to match its colour to the support in which it is going to be applied, it is common practice to have it toasted on a pan or hot plate. Different toasting times allow various degrees of browning of the powdered cellulose. Preparing the cellulose powder at different tones determine the possible limitations of the use of micro-cellulose powder in the long term, some artificially induced degradation tests have been performed. The test results presented in this paper show that the changes occurred are not significant enough to prevent its use in paper conservation. Keywords Microcrystalline powdered cellulose; artificial accelerated ageing; infilling; light bleaching; paper conservation will allow the conservator to pick a colour as similar as possible to the surface of the paper that needs to be matched. Overall, cellulose is a very stable product; but toasting it to give it a certain hue might seem quite a dramatic method regarding its durability, especially when it comes to guaranteeing the best quality and stability of the products applied in conservation treatments. This paper intends to look at the possible alteration of the cellulose after this toasting, the possible side effects and how to diminish or solve these issues, if at all necessary. 2. MATERIALS AND SAMPLES PREPARATION There are several brands of cellulose powder, each one with its own characteristics in relation to particle size. For this study Solka-Floc 300 ® was chosen because its particle size -22 micron- enables a broad range of application methods, providing the conservator more versatility. The samples prepared for the ageing tests intended to be as similar as possible to those that would be used in reality. There are three main methods when using powdered cellulose in paper conservation: • Tamper the dry powder on top of a layer of adhesive previously applied to the support. • Mix the powdered cellulose with an adhesive and apply this mixture over the paper [4]. Figure 1 • Un-aged samples, four toasting degrees, and three different mediums (12 samples).

58 Rita Udina | Amparo Escolano • Prepare a diluted mixture of powdered cellulose and adhesive that will be sprayed in order to obtain very thin films [5]. For this study, the samples were prepared by spraying a mixture of water, adhesive and powdered cellulose on polyethylene terephthalate sheets. This material was chosen because it is chemically inert and dimensionally stable. Three different mediums (synthetic and organic) were selected: Methylcellulose, Aquazol® and isinglass, at the concentration of 1.5%; 5.0% and 1.5% in water respectively. Proportions of adhesive/water were established in relation with their individual adhesive strengths. As for powdered cellulose, four different tones were used: raw (white) cellulose; and toasted cellulose in 3 different degrees, the three of them rinsed twice in tap water (pH 7.14). All in all, 12 different samples (four types of cellulose, applied with 3 different mediums), plus Whatman filter paper, are being studied. 3. ARTIFICIALLY INDUCED DEGRADATION Artificially induced degradation tests intend to accelerate particular damages, but several factors might interact in each context, and it is complex to isolate them and expect that the overall behaviour shall be the same by just summing up those separate factors [6]. Even if far from reality, these tests provide a general idea of material performance that is very useful, particularly for new materials with somewhat unexpected behaviour. The artificially induced degradation tests selected in this study in order to anticipate the behaviour of microcrystalline cellulose consisted in: 1. Long exposure to controlled high temperature at a stable relative humidity. 2. Long exposure to a full spectrum light source. 3. Combination of the two prece- -dents. Each prepared sample was divided in four pieces. One was kept as a control and the other three were exposed to ageing as detailed above. Literature offers a wide choice of artificially induced ageing tests, each of them focused on specific issues regarding ageing conditions and materials, and yet there is no unique protocol to follow [7][8]. When it comes to high temperature exposure, the presence of a certain relative humidity enables some cellulosic hydrolysis processes that wouldn’t take place in dry conditions (unlike reality) [7]. Looking for this similarity to reality the reference ageing of 70ºC, at 70% HR for 15 days was chosen. As for the protocols regarding light damage, the reference was the ASTM D6789-02 Standard Test Method for Accelerated Light Ageing of Printing and Writing Paper by Xenon-Arc Exposure Apparatus [9]. According to it, samples should be exposed for 48 hours under an 800 watt/m2 light source which has been filtered to eliminate radiation under 320 nm. This represents a total amount of 38,400 Watts exposure. 3.1. Controlled high temperature at a stable relative humidity Artificially induced ageing with controlled high temperature at a stable relative humidity was performed in a Boekel Scientific incubator. The samples were exposed during 15 days to a continuous temperature of 70º C with the relative humidity conditioned to 70%. 3.2. Light Light can cause a variety of effects on organic materials (yellowing discolouration, bleaching…). Artificial ageing with light was attained by

The suitability of powdered micro-cellulose for its use in paper conservation 59 exposing the samples to a Light Emitting Plasma (LEP) source. LEP is a full spectrum light source that replicates sun light almost identically, with an intensity of 52,569 lux. The samples were exposed during 188 hours, with a distance of 25 cm between light source and sampled material. Under these conditions a total exposure of 39,690 watts was achieved (almost like the standard, if it wasn’t for 4 extra hours of exposure). No filter was applied in this case, thinking that radiation under 320 nm would not make relevant changes for this purpose (visible range of wavelength). 4. AGEING FACTORS BEING MEASURED Degradation occurs in several levels: photochemical, chemical and physical. These changes might show in diverse factors such as discolouration, acidity or mechanical endurance, for instance. The latter has not been examined in the present study for two main reasons: first because the shortness of the fibres (22 microns) would give no relevant values with the typical tests, such as folding endurance. And secondly, and as a result from the first, because this fibre length prevents any attempt to obtain tissues of significant structural function; actually microcellulose is used in paper conservation mostly as filler, or as a covering material, rather than a structure provider. The possible change on the mechanical endurance after ageing would have a minor impact in terms of the conservation treatment. On the other hand, chemical changes, do have importance because they can alter the support’s chemical context if they prove to be meaningful enough. The study of chemical changes has consisted of pH measurements and the identification, if present, of reducing sugars. Colour changes are the main issue in terms of inpainting since the materials used are intended to be as stable as possible regarding discolouration and fading, hence the importance of this study. The analysis for colour changes was carried out with a Portable Spectrophotometer CM-2600d Konica Minolta. The obtained data was recorded in CIE L*a*b coordinates, where L represents lightness, “a” corresponds to redness-greenness, and “b” to blueness-yellowness. The corresponding changes have been evaluated with euclidean values (DL, Da and Db respectively, and DE as the overall change) [10]. 4.1. Chemical changes: pH variation pH variation is a good indicator of the paper (or cellulose) condition. The measurements were taken with an XS series 8 ver1.0 01/25 surface pHmeter. As expected, ageing involved an acidification of the samples. Light ageing acidified cellulose more than the heat ageing; and samples aged with both light and heat, were the most Table 1 • pH (average per toasting degree)

60 Rita Udina | Amparo Escolano acidic. Acidification has affected less, in general, raw cellulose. The lower slope of its curve (pale blue) compared to the rest, indicates that no toasting makes cellulose more reluctant to suffer acidification after ageing, when compared to toasted samples. Looking at non aged samples (first column in table 1) slightly and medium toasted samples (yellow and orange, respectively) show an unexpected increase of pH compared to raw cellulose, and only the most toasted hue results (in brown) were more acidic than raw cellulose. This difference shortens along the following ageing stages (2nd to 4th columns). A possible explanation to this anomaly is the fact that toasted samples were rinsed twice in tap (slightly alkaline) water. pH before rinsing had not been checked, but it seems likely that the acidification after this toasting was somehow counteracted, or even surpassed, by the alkalinisation of the rinsing water (at a pH of 7.14). In order to analyse acidification despite the possible interference of tap water, let’s observe a table considering the decrease of pH units along the different ageing stages (table 2). It can be stated that heat ageing (first group) is the least acidifying. And, again, the possible interference of tap water alkalinisation is more evident among the toasting degrees within this 1st group. Raw cellulose has proved to keep its pH more stable than the toasted samples in the 2nd (light) and 3rd groups (light & heat aged). In the combination of both light and heat ageing, almost all toasted samples turned out to be more acidic than untoasted cellulose (with the exception of sample #2, yellow, see table 1, 4th column), increasing accordingly to the toasting degree (major toasting implies a more acidic outcome, table 2). Back to table 1, medium toasted samples (yellow and orange) are still, overall, slightly less acidic than untoasted samples. However, the tendency seems to indicate that they would at some point reach the same level and surpass it, for they have the highest rate of acidification (see in table 2: a major decrease of 1.44 units; compared to the maximum decrease of raw cellulose: 0.86; and besides the starting point is higher too: 7.6). 4.2. Benedict’s analysis for reducing sugars Cellulose is a polysaccharide, specifically a homo polysaccharide, because it is formed by a long chain of a unique monomer: glucose. The degradation of cellulose might involve the breakdown of this long chain into its smaller constituents. Therefore at some stage of this degradation Table 2 • Acidificaation rate (ph units) after ageing Figure 2 • From left to right, samples 1 to 5 (and at the very left the one containing glucose) soaked in Benedict and after boiling them for several minutes. Only cellulose #5 gives a positive result (greenish), beside the full positive in an orange-red tone: pure glucose (right).

The suitability of powdered micro-cellulose for its use in paper conservation 61 process, the expected outcome is a certain amount of glucose monomers or other carbohydrates formed by glucose (such as cellobiose). In order to detect the presence of this monomer Benedict’s analysis has been performed, which gives positive results for reducing sugars. Reducing sugars bear a free aldehyde (-CHO) or ketonic (-CO) group in opposition to non reducing sugars, that lack these free groups in their molecules. Reducing sugars include all monosaccharides (i.e. glucose) and many disaccharides (such as cellobiose, which is formed by two glucose monomers). Cellulose is a non reducing sugar. Benedict’s analysis is not quantitative, but qualitative. Nevertheless, the visual result indicates a range of magnitude, which is most useful for this purpose. A negative result implies no colour change (the reagent should remain pale blue), whereas positive results go from green, yellow, orange and brickred. The amount of reducing sugars according to colour should be in these shifts: greenish (500-1000 mg/ dL glucose), yellow (1000-1500 mg/ dL), orange (1500-2000 mg/dL) and full positive is red or brick red (>2000 mg/dL). A negative result implies that the amount of by-products should be none or not higher than 500 mg/dL. The empirical experiment has consisted in analysing 5 different SolkaFloc © samples with Benedict’s reagent: 1. Untreated. 2. Toasted and rinsed twice in tap water. 3. Further toasted, rinsed twice in tap water. 4. Further toasted, rinsed twice in tap water. 5. Further toasted, unrinsed. A sixth sample of pure glucose was added in order to have a positive result to compare with, and to know the boiling time needed to obtain a reliable positive result (shifting colour occurs only after some boiling). While checking the visual results, specially toasted samples (2-5) arise the problem that the brownish hue of the toasted cellulose mixed with the blue Table 3 • Benedict’s test results SAMPLE 1 2 3 4 5 GLUC. Rinsed 2 2 2 2 -- -- Toasting -- -- gr SolkaFloc 0.08 0.10 0.09 0.08 0.08 ~10 drops gr Benedict 1.00 1.52 1.22 1.44 1.40 0.67 Result - - - - + + mg/dL <500 <500 <500 <500 500 ~2000 -1000 reagent made it difficult to determine whether the second had suffered some discolouration or not. To prevent the visual contamination of the reagent’s response, the cellulose samples were wrapped in filter paper, and the cluster was soaked in the reagent, allowing it to react, yet not permitting the cellulose to disperse in the liquid. The results prove that there is no significant amount of glucose (or any other form of reducing sugar, such as cellobiose) in samples 1 to 4. They all kept the reagent unchanged in colour. As for the fifth (most toasted and non-rinsed Solka-Floc ®) it shifted to a greenish hue, meaning that the content of reducing sugars should be not higher than 1000 mg/dL. This outcome should not be surprising, because it is known that cellulose is an extremely difficult polysaccharide to break down [11] (human digestive system cannot do it either) and extreme conditions are required to do so (chemically, at high temperature, greater than 300 ºC, and high pressure, about 25 MPa, or alternatively, enzymatically with cellulases). The conclusion extracted from these results is that the breaking down of cellulose even after a high degree of toasting (sample #5 is dark brown) scarcely jeopardizes the main chain. The by-products derived from

62 Rita Udina | Amparo Escolano this toasting are water soluble and very easily removed with a simple rinsing, or two for more assuredness, in order to avoid any interaction of these by-products with the original support. In summary, toasted and rinsed cellulose has no crucial byproducts derived from the breakdown of the polysaccharide that can be an issue for conservation treatments or the treated objects. 4.3 Colour Changes Colour changes in light aged samples have quite dramatic results, with evident bleaching of the toasted samples. In order to evaluate the tests fairly it must be highlighted that this particular light ageing is far from being a real situation, and it would never occur in normal conditions on stored artwork or even exhibitions. An exposure of 188 hours at 52,569 lux means almost 10 million lux hours (9,882,972 lux hours) which is like 392 times an average exhibition of 25,200 lux hours (50 lux 7 hours a day, 6 days per week during 12 weeks). The results might seem anyway somehow contradictory, since accelerated ageing induced by heat involved a slight darkening (not perceptible by the naked eye for the less toasted samples, and scarcely perceptible for the more toasted ones), whereas light ageing implied a notorious bleaching. Samples with both ageing processes were even more faded than those exposed only to light. Although the difference within these two is not remarkable, it can be striking that heat ageing darkens, light ageing causes a strong lightening/brightening, and both -heat and light aging- fade even more than the latter, not something in between. It seems like already damaged fibres are more sensitive to discolouration than fibres in better condition (let it be noted that heat ageing was done prior to light ageing in the samples aged with both processes). Figures 4 and 5 correspond to the evolution on isinglass samples along ageing and toasting, which is similar in the other two mediums. In all of the samples light bleaching is more noticeable the more toasted the samples are. However, the main visual change turned out to be fading and not yellowing or darkening as expected. Analysing the obtained values of CIE L*a*b it can be stated whether the colour change is imperceptible (DE<0.5), noticeable (0.5<DE<1.6) or unacceptable (DE>3.2) [10]. Figure 3 • 3rd toasting degree samples. Rows from top to bottom: both aging methods, light ageing, heat ageing, not aged. Columns from left to right: Aquazol medium, methyl cellulose, isinglass. Figure 4 • Untoasted SolkaFloc (sample #1) prepared with isinglass at different ageing stages. Lower values involve darker colours. The major change occurs in the blueish wavelength (meaning there is a yellowing/bleaching).

The suitability of powdered micro-cellulose for its use in paper conservation 63 Whatman paper has a model behaviour at any ageing stage, with imperceptible DL (: -0.19; : 0.07 and : -0.02) and just noticeable DE change at any stage (: 0.73; : 0.91 and : 0.93). Heat ageing involved some yellowing in all the samples (Db>0), whereas light ageing and both ageing methods implied the contrary (negative Db, meaning some blueing, or less yellowing). The observation of Da values (red/ green colour) is related to the variation of the toasting hue. Their values are much smaller than Db, and they do not provide relevant information to this study, or it is difficult to say, since variations do not have such a direct relationship to ageing, like Db. As for mediums, their behaviour is quite similar. Methyl cellulose (MC) has the best performance in terms of stability, and Aquazol® goes last. But we cannot judge the latter in equal conditions to isinglass and MC, because it had a concentration 3 times bigger. When considering the total amount of change (DE) it is still complex to see a straight forward relationship, but in general terms it can be stated that no toasting involves an acceptable discolouration at any ageing stage (DE<1.78 in the worst case). Further toasting increases these values, where some of the light and medium toasted samples can be found still in the acceptable change range, yet noticeable (maximum values are for #4 toasting, for both methyl cellulose and isinglass, with DE around 3.0). Heat ageing is the least damaging, whereas both heat and light ageing have the worst results. Most of the samples with major unacceptable colour change fall into light ageing and both ageings (#4 isinglass, #2 MC and #3 Aquazol provide the maximum rates, all of them at light or heat & light ageing: DE= 25, 26 and 27 respectively). When placing into context the values (being aware that the light exposure ageing was unfiltered, unlike most cases in reality) it can be concluded that the results are convenient for the case of inpainting as long as some precautions are taken into account (rinsing and using only slightly toasted cellulose). Being the case that some colour fading occurs, it might be easily corrected by the addition of some colouring (watercolour, pastel, or whichever technique suits for each particular case). And secondly but not less important, fading will never be perceived as a stain, unlike situations in which darkening happens. Also, In terms of criteria it is accepted that inpaintings be slightly paler than the original surrounding paint, so, unless the fading is very pronounced, it might not always be necessary to re-match a faded inpainting. And last, but not least, a filling with microcrystalline cellulose will not become darker than the original, as long as the initial filling wasn’t. 5. CONCLUSIONS Chemical changes after ageing in the tested material are minor and should not discourage its use, as long as a proper rinsing is made. The breaking down of the cellulose chain even after a high degree of toasting is negligible, and a slight decrease in the pH can be easily corrected with the addition of a base such as calcium hydroxide. In relation to discolouration it is good to know that shifting occurs in a way – fading – which is not perceived as a stain. In the worst case of bleaching the cellulose inpainting can be easily adjusted, if necessary, Figure 5 • Toasted SolkaFloc (sample #4) prepared with isinglass. The target (in red) is now darker compared to untoasted cellulose (previous image). Difference between ageing stages are bigger too. #2 and #3 have curves accordingly to this evolution.

64 Rita Udina | Amparo Escolano without replacing the whole infill. However, it would be a smart precaution to prevent this undesired effect at any rate on the long term by using only slightly toasted hues, and adjust the darkest colours by other means, either adding pigments or dyeing raw cellulose. Ageing tests are thought to reveal unknown information, hence the impossibility to customize them previously to match the desired data. Further studies should be made to obtain more specific results. Chemical degradation study could be improved with viscosity analysis (not possible with the present samples because of their low weight); pH measurements following the Tappi standard (cold or hot extraction), and light ageing at shorter exposure with the appropriate filter. ACKNOWLEDGEMENTS Centre de Restauració de Béns Mobles de Catalunya (Spain), providing most useful resources for analysis (spectrophotometer and pHmeter). Special thanks to Ricardo Ruiz, Maite Toneu and Ruth Sadurní. Dr. Ainhoa Nieto (Scripps Research Institute) for her help with the heat ageing chamber. J. Jerónimo Perez-Escolano for his help with proofreading and editing this article. REFERENCES [1] FUTEMICK, Robert et al. 1987 Filling Losses. Chap. 26 in Paper Conservation Catalogue. Washington D.C.: American Institute for Conservation Book and Paper Group https://goo.gl/Hk8Epv (accessed 08/08/2017) [2] SCHENCK, Kimberly et al. 1994 Inpainting. Chap. 30 in Paper Conservation Catalogue. Washington D.C.: American Institute for Conservation Book and Paper Group https://goo.gl/5wWFYg (accessed 08/07/2017) [3] POULSON, Tina Grette - Retouching Art on Paper. London: Archetype, 2008. [4] BERNSTEIN, James; EVANS, Debra – Cellulose powder for fills and compensation. In Mastering Inpainting. FAIC workshop manual. San Francisco, CA. 2010. [5] O’LOUGHLIN, Elissa; JEWELL, Stephanie – Two New Techniques for Loss Compensation in Art on Paper: Integration of Surface Losses Using Textile Fibers and the Use of Sprayed Cellulose Powder to Minimize Foxing and Other Discoloration. The Book and Paper Group Annual. Nº 32 (2013), pp. 52. [6] FELLER, Robert L. – Accelerated Aging: Photochemical and Thermal Aspects. BERLAND, Dinah, ed. – Research in Conservation, 4. USA: The Getty Conservation Institute, 1994, pp. 115. [7] GARCÍA HORTAL, José Antonio – Fibras papeleras. Barcelona: Ediciones UPC, 2007. pp. 46 [8] PORCK, Henk J. – Rate of Paper Degradation. The Predictive Value of Artificial Aging Tests. Amsterdam: European Commission on Preservation and Access, 2000. [9] Standard Test Method for Accelerated Light Aging of Printing and Writing Paper by Xenon-Arc Exposure Apparatus ASTM D6789- 02 (2007). West Conshohocken, PA: ASTM International, 2007 (withdrawn 2011). [10] MICHALSKY, Stefan; DIGNARD, Carole – Ultrasonic misting. Part 1: Experiments on appearance change and improvement in bonding. JAIC. Vol. 36, nº2 (1997) pp. 109-126. [11] JIN, Xi – Breaking Down Cellulose. In the course Physics 240: Introduction to the Physics of Energy. Stanford University, November, 2010. https://goo.gl/Kb5kUi (accessed 05/25/2017) Postprints

Nome artigo 65

Abstract In this research project we propose a new material usable for the preparation of retouching colours as an alternative to the more common watercolours normally used for the pictorial restoration of the artworks. Compared to traditional Arabic gum based watercolours, the self-produced colours here presented are made with a new synthetic binder: Aquazol® 500. This polymer has good physical-chemical properties and a wide spectrum of solubility in various organic polar solvents, which also makes it suitable for the retouching of water sensitive artworks. These new retouching colours with Aquazol® 500, prepared with two different recipes, were investigated with different scientific analyses both before and after artificial aging in a Solar Box, in order to evaluate their stability over time. THE USE OF AQUAZOL® 500 AS A BINDER FOR RETOUCHING COLOURS: ANALYTICAL INVESTIGATIONS AND EXPERIMENTS Vanessa Ubaldi (1) | Roberto Bestetti (3) | Roberto Franchi (1) | Emanuela Grifoni (6) | Pier Paolo Lottici (4) | Francesca Modugno (5) | Richard Wolbers (2) | Daphne De Luca(1) 1. University of Urbino Carlo Bo, Department of Pure and Applied Sciences, Conservation and Restoration of Cultural Heritage; Via Aurelio Saffi 2, 61029 Urbino (PU), Italy: [email protected]; [email protected]; [email protected] 2. University of Delaware, Department of Art Conservation; 303 Old College, Newark, DE 19716, USA: [email protected] 3. Association CESMAR7, Centre for the Study of Materials for Restoration; Viale Dei Mille 32, 42121 Reggio Emilia (RE), Italy: [email protected] 4. University of Parma, Department of Mathematical, Physical and Computer Sciences; Parco Area delle Scienze 7/A, 43124 Parma (PR), Italy: [email protected] 5. University of Pisa - Department of Chemistry and Industrial Chemistry; Via Giuseppe Moruzzi 13, 56124, Pisa (PI), Italy: [email protected] 6. Applied and Laser Spectroscopy Laboratory, Institute of Chemistry of Organometallic Compounds, Research Area of National Research Council(CNR); Via G. Moruzzi, 1 – 56124, Pisa (PI), Italia: [email protected]

1. INTRODUCTION The research consists of proposing a new material to be used for the preparation of retouching colours for the retouching of artistic artefacts, experimenting with alternative colours to the common watercolours which are found on the market today, usually used for pictorial retouching of artworks [1-5]. These colours differ from the traditional Arabic gum based watercolours precisely for the use of a new synthetic binder: Aquazol® 500. This polymer has good physical-chemical properties and a wide spectrum of solubility in The results obtained from the study of the self-produced colours were then compared with those obtained from the same scientific investigations carried out on the only commercial watercolours based on Aquazol® currently on the market: QoR® by Golden Artist Colors (USA). The results obtained from the study demonstrate that, thanks to its extreme stability, Aquazol® 500 can be considered a valid binder for retouching colours. In fact, the polymer does not degrade and does not show crosslinking phenomena. The self-produced colours are confirmed to be much more stable over time and therefore much more suitable than the QoR® watercolours for pictorial retouching of artistic artefacts. Keywords Aquazol® 500; Retouching colours; Watercolours; QoR®; Artificial aging; Stability. various organic polar solvents, with relatively low toxicity, which make it an extremely versatile material especially when used as a binder for retouching colours. Its positive characteristics and above all, its peculiarity of being soluble in many solvents, not only in water [6- 8], enable us to produce colours that can be used for the retouching of any type of artistic artefact, including those that are water sensitive. In this way, a limitation of the usual watercolours made of gum Arabic, which are soluble solely in water and cannot be used for the retouching of all water-sensitive surfaces such as contemporary artworks, can be overcome. Another reason that has lead to this new formulation of retouching colours is the fact that the composition of watercolours that are found on the market today, and that are used in the conservation field, is not always known. In fact, the manufacturing firms usually indicate only in general terms the composition of the colours sold, to protect patents. Unfortunately, the lack of precise information and the substitution or variation of the ingredients in the composition of commercial colours means that in these colours there may be substances which are unstable over time, of which the restorer is unaware. These are the main causes of chromatic alterations that commercial watercolours show. Moreover, the colours that we find on the market are made with a precise balance between all their ingredients, and they cannot be changed, but if restorers are able to self-produce colours for pictorial retouching, then they can change this balance according to their own needs, and decide on the composition of the colours to use. For these reasons, and especially because the colours used for pictorial retouching, like all materials used for restoration, must be stable and reversible over time, it was

68 Vanessa Ubaldi | Roberto Bestetti | Roberto Franchi | Emanuela Grifoni | Pier Paolo Lottici | Francesca Modugno | Richard Wolbers | Daphne De Luca decided to experiment with this new formulation of retouching colours. In this way, when restorers self-produce colours using known ingredients, of which the physical-chemical composition and characteristics are known, because they have been tested and studied especially for this aim, they can be sure they are using colours which are stable and durable over time, something not guaranteed by commercial colours. The aim of the research was to create self-produced colours based on Aquazol® 500, characterizing the materials that make these and analysing the chemical-physical characteristics of the colour samples before and after artificial ageing in a Solar Box, to evaluate their stability over time. To characterize the materials used to prepare the colours and to identify possible interactions between the binder and the pigments combined with it, different scientific analyses were used, chosen considering the substances to be analysed and the information to be obtained. These were also used to observe any differences between the two recipes used to prepare the self-produced colours and to understand which of the two is the best one to use for the preparation of colours based on Aquazol® 500. The recipes used are: • Recipe A: composed of Aquazol® 500 dissolved in demineralized water, pigments, glycerin, xanthan gum and 2-phenoxyethanol; • Recipe B: composed of Aquazol® 500 dissolved in demineralised water, pigments and 2-phenoxyethanol. The two recipes differ only in the addition of the two additives introduced in Recipe A: glycerine and xanthan gum. The idea of making these two recipes was inspired by the studies conducted by R. Wolbers, who was the first to use Aquazol® as a pigment binder [9]. He suggested adding xanthan gum to the colour preparation recipe, which helps pigment dispersion in the binder, and glycerin, which improves the workability of the colours. Wolbers argues that to create a uniform and homogeneous colour, it is necessary to add a substance to help the dispersing of the pigment, because it is possible that Aquazol® alone cannot disperse it completely, creating lumpy and non-homogeneous colours which, over time, can undergo chromatic alterations, mechanical variations of the pictorial film, or in the worst cases, the separation of the binder from the pigments. The comparison of these two recipes was investigated to discover if the addition of these additives would affect workability and especially colour stability over time. The results obtained from the study of the colours produced with these two Recipes A and B were then compared with those obtained from the same scientific investigation carried out on the only commercial watercolours based on Aquazol® currently on the market: QoR®. These watercolours were introduced on the market in May 2014 by Golden Artist Colors (USA), the company that today produces and distributes these only in the United States. They were included in the study for two reasons. Firstly, because they are based on Aquazol®, it is important to make a comparison with self-produced colours that are made with the same binder. The second reason is that the ingredients used to prepare the QoR® are not known, because the manufacturer does not specify the components present in the colours and does not even indicate which of the four molecular weights of Aquazol® was used to make them. For these reasons, the self-produced colours with the two Recipes A and B were compared to the commercial colours QoR® to discover if there are differences and similarities between these two types of colours and to understand which are the best ones to use for pictorial retouching of artworks, considering the stability and durability parameters over time, tested

The use of Aquazol® 500 as a binder for retouching colours: analytical investigations and experiments 69 with the artificial aging of the samples. 2. MATERIALS AND METHODS 2.1 Materials Used The materials used for preparing the self-produced colours were as following: • Binder: Aquazol® 500, sold by Kremer Pigmente GmbH & Co. KG.; of the four existing molecular weights, it was chosen because it is composed of larger molecules which remain on the surface to which it is applied and do not penetrate the substrate, a feature that a retouching colour should have in view of its future reversibility. • Additives: xanthan gum and glycerin (glycerol), present only in Recipe A. The xanthan gum was purchased from the Italian company “La Saponaria, cosmetica consapevole” that sells raw materials for the personal production of natural cosmetics. This gum was chosen because usually gum used in the cosmetics field for the preparation of creams has a clear grade, an essential feature to consider when choosing this material. In fact, a gum with a yellowish colour could alter the tone of the prepared colours, and for this reason, is not recommended. The glycerol was purchased by Kremer Pigmente GmbH & Co. KG. • Preservative: 2-phenoxyethanol purchased from Sigma-Aldrich S.r.l.. This preservative was added to colours to avoid the formation of microorganisms and in particular, moulds. • Pigments: a limited number of inorganic and organic pigments were selected to be added to the binder prepared with Recipes A and B. Taking as reference the twelve colours used to perform pictorial retouching from the high school of Rome, the Institute for Conservation and Restoration (ISCR), ten pigments were selected in total, seven inorganic and three synthetic organic purchased from two different companies: an Italian company of Verona, Dolci Colori Srl, which provided the seven inorganic pigments (Table 1), and a German company, Kremer Pigmente GmbH Table 1 • Seven inorganic pigments PRODUCING COMPANY PIGMENT NAME PRODUCT CODE COLOUR INDEX INTERNATIONAL GENERIC NAME CONSTITUTION NUMBER Dolci Colori Titanium White 7525/1 PB/0241 Pigment White 6 77891 Dolci Colori Pure Ultramarine Blue PA/0561 Pigment Blue 29 77007 Dolci Colori Cadmium Red Medium 3540 PA/0554 Pigment Red 108 77202 Dolci Colori Ocher icles Lemon TR/0324 Pigment Yellow 43 77492 Dolci Colori Green Chromium Oxide Hydrate PA/0601 Pigment Green 18 77289 Dolci Colori Burnt Sienna TOR/SA TR/0262 Pigment Brown 7 77492 Dolci Colori Ivory Black PA/0597 Pigment Black 9 77267

70 Vanessa Ubaldi | Roberto Bestetti | Roberto Franchi | Emanuela Grifoni | Pier Paolo Lottici | Francesca Modugno | Richard Wolbers | Daphne De Luca & Co. KG, which provided the three organic pigments (Table 2). The three synthetic organic pigments are not present in the colours used by the ISCR and are usually excluded from the restorer’s palette because they are considered unstable over time and therefore not suitable for pictorial retouching. Based on these considerations, it was decided to include these in the study, to investigate their stability when exposed to accelerated aging. Since alizarin is a very useful colour for pictorial retouching, it was decided to test the stability and durability of Alizarine Crimson Dark, as well as two substitutes: Irgazine® Ruby DPP TR can be considered an excellent substitute for dark alizarin, while Quindo® Pink D is a valid alternative to light alizarin. The objective was to discover whether the alternatives could both be used for pictorial retouching, and if alizarin was found to be unstable, then if one substitute was better than the other. Table 2 • Three organic synthetic pigments PRODUCING COMPANY PIGMENT NAME PRODUCT CODE COLOR INDEX SPECIFIED BY THE COMPANY GENERIC NAME CONSTITUTION NUMBER Kremer Pigmente Alizarine Crimson Dark 23610 Pigment Red 83 58000:1 Kremer Pigmente Irgazine® Ruby DPP TR 23182 Pigment Red 264 561300 Kremer Pigmente Quindo® Pink D 23402 Pigment Violet 19 73900 Table 3 • Seven inorganic QoR® PRODUCING COMPANY PIGMENT NAME PRODUCT CODE COLOR INDEX INTERNATIONAL GENERIC NAME SPECIFIED BY THE COMPANY Golden Artist Colors Titanium White 7000535 Pigment White 6 Golden Artist Colors Ultramarine Blue 7000310 Pigment Blue 29 Golden Artist Colors Cadmium Red Medium 7000215 Pigment Red 108 Golden Artist Colors Yellow Ochre (Natural) 7000440 Pigment Yellow 43 Golden Artist Colors Viridian Green 7000380 Pigment Green 18 Golden Artist Colors Burnt Sienna (Natural) 7000470 Pigment Brown 7 Golden Artist Colors Ivory Black 7000505 Pigment Black 9 -Aquazol® based commercial watercolours, the QoR®: ten QoR®, seven inorganic (Table 3) and three organic (Table 4) have been selected to compare with selfproduced colours. The parameter used to choose the ten QoR® was the Colour Index ™ Generic Name, which describes a commercial product for its specific use class, its tonality, and a serial number, referring to the ten pigments used to prepare self-produced colours. 2.2 Preparation of the samples The proportions of the ingredients used to prepare the colours with the two Recipes A and B were chosen taking into consideration the material and guidelines provided by Professor Richard Wolbers during the Workshop on Aquazol® in Turin in 2014 [10] and the indications and advice that the Professor provided. Wolbers has divided different types of pigments into five categories and for each of these, has identified the right percentage of binder to be

The use of Aquazol® 500 as a binder for retouching colours: analytical investigations and experiments 71 Table 4 • Three organic QoR® PRODUCING COMPANY PIGMENT NAME PRODUCT CODE COLOR INDEX SPECIFIED BY THE COMPANY GENERIC NAME Golden Artist Colors Permanent Alizarin Crimson 7000240 Pigment Red 177 Golden Artist Colors Pyrrole Red Deep 7000225 Pigment Red 264 Golden Artist Colors Quinacridone Red 7000235 Pigment Violet 19 combined with pigment powder to create a homogeneous and uniform colour. Pigments with the same characteristics and those composed of similar particles have been grouped into a single category. The Table 5 • Recipe A: Preparation of the five solutions of Aquazol® 500 PREPARED SOLUTIONS PIGMENT CATEGORIES TO ADD TO THE 5 SOLUTIONS % AQUAZOL® 500 IN GRANULAR FORM DISSOLVED IN DEMINERALIZED WATER QUANTITY OF GLYCERIN QUANTITY OF XANTHAN GUM QUANTITY OF 2-PHENOXYETHANOL 1 1° Category 40% 4 drops in a solution of 100 ml 0,04 gr in a solution of 100 ml 4 drops in a solution of 100 ml 2 2° Category 35% 3 3° Category 30% 4 4° Category 25% 5 5° Category 20% Table 6 • Recipe B: Preparation of the five solutions of Aquazol® 500 PREPARED SOLUTIONS PIGMENT CATEGORIES TO ADD TO THE 5 SOLUTIONS % AQUAZOL® 500 IN GRANULAR FORM DISSOLVED IN DEMINERALIZED WATER QUANTITY OF 2-PHENOXYETHANOL 1 1° Category 40% 4 drops in a solution of 100 ml 2 2° Category 35% 3 3° Category 30% 4 4° Category 25% 5 5° Category 20% choice of the percentage of binder to be added to the five pigment categories is based on the CPVC parameter, Critical Pigment Volume Concentration[11], which identifies the optimum concentration of pigment to be added to the binder, considering the physical and morphological characteristics of the grains that make up the pigment powder (Table 7). 1. FIRST PHASE - PREPARATION OF AQUAZOL® 500 USING RECIPES A AND B: five different binder solutions were prepared with Recipe A (Table 5) and five with Recipe B (Table 6). Out of the five solutions prepared with Recipes A and B, only one was selected, the one with the

72 Vanessa Ubaldi | Roberto Bestetti | Roberto Franchi | Emanuela Grifoni | Pier Paolo Lottici | Francesca Modugno | Richard Wolbers | Daphne De Luca 20% Aquazol® 500 prepared with both recipes. This was applied on a microscope slide to then undergo scientific investigation. 2. SECOND PHASE - Preparation of the self-produced colours with Recipes A and B: The self-produced colours were obtained by mixing the binder solutions prepared with Recipes A and B with the ten selected pigments, divided into the five categories identified by Wolbers (Table 7: the ten pigments used, corresponding to the pigments subdivided by Wolbers into the five categories, are highlighted with the same colour). Twenty colours were prepared: ten with Recipe A and ten with Recipe B. Table 7 • Preparation of the twenty self-produced colours: Recipes A and B PIGMENT CATEGORIES PIGMENTS DIVIDED BY WOLBERS IN 5 CATEGORIES 10 PIGMENT USED WHICH CORRESPOND TO THE CATEGORIES INDICATED BY WOLBERS % PIGMENT TO TAKE INCONSIDERATION ON THE VOLUME OF THE CORRESPONDING BINDSOLUTION 1° Category Phthalocyanines Red Quinacridones Dioxazine Violet Alizarin Crimson Quindo® Pink D - 23402 15% 2° Category Prussian Blue Carbon Black Red Iron Oxides (uncalcinated) Zinc White Titanium White Yellow Quinacridones, Benzimidazolones Synthetic organic pigments Titanium White 7525/1-PB/0241 Alizarine Crimson Dark - 23610 Irgazine® Ruby DPP - TR - 23182 25% 3° Category Yellow Iron Oxide Viridian Ultramarine blue Ultramarine violet Cobalt Pigments (blue, cerulean, turquoise, green) Ocher icles lemon TR/0324 Green Chromium oxide hydrate PA/0601 Pure ultramarine blue PA/0561 35% 4° Category Cadmium Yellow Cobalt Violet Red and Yellow Iron Oxides (calcined) Ivory Black PA/0597 Burnt Sienna TOR/SA-TR/0262 45% 5° Category Cadmium Orange Cadmium Red Manganese Violet, Manganese Blue Cadmium red medium 3540 - PA/0554 50% The colours were prepared by mixing together the right amount of binder and pigment and were worked with a glass pestle to obtain a homogeneous compound without clumps. Subsequently they were applied on the microscope slides before undergoing scientific investigation.

NTO TOTAL DING % OF AQUAZOL® 500 IN SOLUTION PREPARED WITH RECIPE A AND B TO BE MIXED WITH THE CORRESPONDING PERCENTAGE OF PIGMENT Aquazol® at 40% in solution (Recipes A e B) Aquazol® at 35% in solution (Recipes A e B) Aquazol® at 30% in solution (Recipes A e B) Aquazol® at 25% in solution (Recipes A e B) Aquazol® at 20% in solution (Recipes A e B) The use of aquazol® 500 as a binder for retouching colours: analytical investigations and experiments 73 3. THIRD PHASE- Preparation of commercial watercolours QoR®: these are sold in tubes that are ready for use. They were only diluted with demineralized water and applied on microscope slides to then undergo to scientific investigations. 2.3 Scientifics Investigations The experimentation is structured in different phases that can be summarized as follows: 1. Study of inorganic and organic pigments; 2. Study of binder: Aquazol® 500 granular form and in solution at 20% prepared with Recipes A and B; 3. Study of additives: xanthan gum and glycerin; 4. Study of self-produced colours based on Aquazol® 500: Recipes A and B; 5. Study of commercial watercolours based on Aquazol®: QoR®; 6. Comparison between QoR® and self-produced colours with Recipes A and B. For each phase, different scientific investigations were used, aimed at characterizing and studying Aquazol® based colours and the materials that compose them. The scientific investigations used were as follows: • Stereo Microscope: to obtain morphological information on samples colours before and after artificial aging, to see any changes on the surface of the colours, such as craquelures and lifting paint; • X-ray Diffractometer (XRD): to have information on the crystalline phases present in the analysed inorganic pigments and to make a comparison with the data obtained by Raman Spectroscopy, to obtain as much information as possible on the composition of the pigments used to prepare the self-produce colours; • Colorimetric investigation: to identify the relevant colorimetric values for each colour and for binder solutions, to highlight any changes due to artificial aging; • Raman spectroscopy: to characterize pigments, binders, and additives and observe if the self-produced colours and QoR® analysed before and after aging presented any changes. Through this technique it was also desired to assess whether the pigments mixed with Aquazol® 500 can interact with it, and if the pigments present in the self-produced colours are the same used in the preparation of QoR®; •Attenuated total reflectance-Fourier Transform-Infrared spectroscopy (ATR-FT-IR) and Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS): to obtain qualitative information on the organic pigments, the binder, and additives. This was also used to obtain information about the binder solutions, the organic selfproduced colours and on equivalent QoR®, before and after aging, for two reasons. Firstly, to discover if there are differences in ATR-FT-IR spectra caused by deterioration processes: such as

74 Vanessa Ubaldi | Roberto Bestetti | Roberto Franchi | Emanuela Grifoni | Pier Paolo Lottici | Francesca Modugno | Richard Wolbers | Daphne De Luca the formation of oxidation processes or other degradation processes. Secondly, to observe any changes in the chromatographic profile of the samples that could indicate the crosslinking phenomena of the polymer; • Thermogravimetry (TGA): to investigate the physical-chemical properties of the solid binder and the organic pigments. This was also used to analyse, before and after aging, the samples of the binder in solutions and only one of the organic self-produced colours, the Irgazine® Ruby DPP-TR, and the equivalent QoR®, Pyrrole Red Deep, to observe the potential changes of temperature of the thermal degradation of the mixtures of colour [12]; • High-performance liquid chromatography with diode-array detection (HPLC-DAD): to obtain qualitative information on two organic pigments, Alizarine Crimson Dark and Quindo® Pink D to compare with those obtained from the study of the two homonymous organic selfproduced colours with the Recipes A and B, and the two corresponding organic QoR®, Permanent Alizarin Crimson and Red Quinacridone, in order to assess whether the pigments used in the QoR® are effectively the same as those used for the preparation of self-produced colours [13]; • High-performance liquid chromatography coupled to electrospray ionization and quadrupole time-of-flight (HPLCESI-Q-TOF): to characterise the QoR® Permanent Alizarin Crimson which during the experimentation showed a different composition from the corresponding Alizarine Crimson Dark pigment used to prepare the homonymous self-produced colour with Recipes A and B; • Laser Induced Breakdown Spectroscopy (LIBS): to characterise the possible presence of inorganic substances used as complexing agents in the organic pigments and in the un-aged organic QoR®. In fact, it is noted that organic pigments, being neither mineral nor natural substances, are fixed on semi-transparent inert matrices of inorganic origin, usually made of hydrated oxide of aluminium, to become insoluble pigments in the medium in which they are dispersed; • Artificial aging: the samples were subjected to artificial aging in Solar Box with irradiation in the visible spectrum to check their stability over time. Indoor aging was simulated, and the samples were subjected to just one cycle of aging with a total radiation exposure of 777 hours with a light intensity equivalent to 1181 MJ/ m2 . 3. RESULTS AND DISCUSSION The results concerning the characterization of the inorganic pigments analyzed in XRD and Raman Spectroscopy showed that the chemical composition of the pigments indicated in the technical and safety data sheet is not always fully accurate. In fact, the following pigments have shown the presence of undeclared substances: • Titanium White 7525 (PB/0241) and Red Cadmium Medium 3540 (PA/0054): both contain calcite which usually does not characterize these two inorganic pigments; • Burnt Sienna TOR/SA (TR/0262): contains calcite, dolomite and anatase (titanium dioxide), not declared by the company. Out of the three organic colours, initially characterized in Raman Spectroscopy, and then in TGA, ATRFT-IR and LIBS, only two present undeclared inorganic substances: • Alizarin Crimson Dark: contains titanium (chemical element) which is not reported on either the technical data sheet or the safety data sheet of pigments. • Irgazine® Ruby DPP-TR: contains an inorganic matrix not declared by the company, consisting of calcium, magnesium and aluminium.

The use of aquazol® 500 as a binder for retouching colours: analytical investigations and experiments 75 The experimentation conducted on Aquazol® 500 based colours confirmed the chemical stability of the polymer, which can then be used with success as a binder of retouching colours. In fact, the results obtained by TGA investigation carried out on the binder in solution (Recipes A and B) indicate that there are no important increases of temperature of polymer degradation as a consequence of aging, which means that the polymer neither degrades nor shows cross-linking phenomena. Furthermore, there are no substantial differences between the binders prepared with Recipes A and B. For this reason, both can be used to prepare the self-produced colours, since they are stable and durable over time and the presence of the additives does not influence the chemical-physical characteristics of the polymer. Therefore, it will only be at the discretion of the restorer to decide which of the two recipes must be used, bearing in mind that Recipe A, which differs from B only for the presence of the two additives, produces colours which are easier to apply and in which the pigment is better dispersed. After the aging process, the self-produced colours do not show surface morphological change. Moreover, the pigments which constitute them, do not interact with the binder, giving rise to the formation of new substances, therefore are stable both chemically and physically Even the colorimetric data suggest that the self-produced colours after aging are stable and do not show important chromatic alterations, therefore can be safely used for pictorial retouching of artworks. The only inorganic colours that have shown evident chromatic changes after aging are: • Pure Ultramarine Blue, prepared with both Recipes A and B that darkened, confirming the data reported from the recent scientific studies regarding ultramarine watercolours [14]. For this reason, it would be preferable to find a valid substitute, or at least to use the colour made with Recipe A, which darkens less than the one prepared with Recipe B. • Burnt Sienna prepared with Recipe B that slightly blackened and turned yellow, whilst the colour prepared with Recipe A did not change. It is hypothesized that this different response to aging depends on the dispersion of the pigment in the binder and therefore the one prepared with Recipe A, that contains xanthan gum which helps the dispersion of the pigment in the binder, is more homogeneous and alters less than that prepared with Recipe B. Therefore, the use of colour prepared with Recipe A is suggested. In the study carried out on the three self-produced organic colours, it was found that Alizarine Crimson Dark prepared with both Recipes A and B tends to darken with time, confirming the instability of this colour. For this reason, its use is not recommended. The use of the two substitute colours tested is suggested because after aging they remained stable and did not undergo noticeable chromatic variations. As a substitute for light alizarin, Quindo® Pink D can be used, prepared with both Recipes A and B, whereas as a substitute for dark alizarin, Irgazine® Ruby DPP TR can be used, prepared with Recipe B, because it is observed that the one prepared with Recipe A, although stable, is more subject to chromatic variations over time. The comparison between selfproduced colours with QoR® has highlighted some discrepancies in composition between these two types of colours and differences in their behaviour following aging. In fact, after aging, two organic QOR® have shown differences in comparison to the corresponding self-produced colours: • QoR® Permanent Alizarin Crimson is made up of a pigment

76 Vanessa Ubaldi | Roberto Bestetti | Roberto Franchi | Emanuela Grifoni | Pier Paolo Lottici | Francesca Modugno | Richard Wolbers | Daphne De Luca different to that identified in the corresponding self-produced colour Alizarin Crimson Dark (Recipes A and B): QoR® is composed of dimer 1-amino-9,10-anthraquinone and not alizarin, which is a 1,2-dihydroxyanthraquinone, present in the corresponding self-produced colour. • QoR® Pyrrole Red Deep shows a chemical transformation unobserved in the corresponding self-produced colour Irgazine® Ruby DPP-TR (Recipes A and B). It is hypothesized that these differences also affected the stability of QoR® colours. In fact, the colorimetric data indicate that the use of QoR® Pyrrole Red Deep and of the other substitute tested, QoR® Quinacridone Red, is not recommended because they undergo obvious chromatic alterations over time. For this reason, in contrast to organic selfproduced colours, it is preferable to use QoR® Permanent Alizarin Crimson, which is more stable than the two QoR® substitutes and corresponding self-produced colour because it is not composed of alizarin (1,2-dihydroxyanthraquinone). Compared to self-produced colours (Recipes A and B), QoR® colours have proven to be less stable and durable over time. In fact, they undergo more chromatic variations, since out of ten QoR® samples, five darkened and turned yellow as a consequence of aging: QoR® Yellow Ocher Natural, Ultramarine Blue, Viridian Green, Quinacridone Red, and Pyrrole Red Deep have been in fact altered. 4. CONCLUSIONS Based on the results obtained, considering the terms of stability and durability over time, one can conclude that the self-produced colours are better than the commercial colours and therefore more suitable for pictorial retouching of artistic artefacts. It would be desirable to continue this research on Aquazol® 500 based colours to study in more depth their reversibility, and their application on various types of artefacts, including contemporary artworks such as alkyd, vinyl, and acrylic paints. Developing an analytical protocol, it would be possible to identify, based on the surface to be retouched, the best solvent to be used for both application and re-solubilization of the colours, and to investigate if, after their removal, there are any traces of residues on the surface, or within the preparatory and pictorial layers of the samples prepared in the laboratory, made with different painting techniques. The final scope is to create selfproduced colours with characteristics suitable from an aesthetic and conservation point of view, so that the restorer can self-produce stable and reversible retouching colours with known composition and chemicalphysical characteristics.

The use of aquazol® 500 as a binder for retouching colours: analytical investigations and experiments 77 ACKNOWLEDGMENTS The authors acknowledge: Prof. Danilo Bersani and Prof. Claudio Oleari of the University of Parma (Department of Mathematical, Physical and Computer Sciences); Dr. Jacopo La Nasa, Dr. Sibilla Orsini, Dr. Fiammetta Di Marco, Dr. Maria Rosaria Tinè, Dr. Celia Duce, Dr. Alessio Spepi, Dr. Ilaria Degano and Dr. Francesca Sabatini of the University of Pisa (Department of Chemistry and Industrial Chemistry); Dr. Stefano Legnaioli of the Institute of Chemistry of Organometallic Compounds, National Research Council (CNR) of Pisa (Applied and Laser Spectroscopy Laboratory); Dr. Valentina Emanuela Selva Bonino of the Association CESMAR7 (Center for the Study of Materials for Restoration). We are also grateful to Prof. Maria Perla Colombini and Dr. Emma Cantisani for having made the Solar Box available at the Institute for the Conservation and Valorisation of Cultural Heritage (ICVBC) of the National Research Council (CNR) of Florence. REFERENCES [1] UBALDI, Vanessa - Self-produced Colours Based on Aquazol® 500. In DE LUCA, Daphne (Edited by) - Preservation and Conservation of Canvas Paintings. Collection of Fundamentals of Cultural Heritage Preservation and Conservation, 3rd edition, Il Prato, 2018, in press. [2] LA NASA, Jacopo; DI MARCO, Fiammetta; BERNAZZANI, Luca; DUCE, Celia; SPEPI, Alessio; UBALDI, Vanessa; DEGANO, Ilaria; ORSINI, Sibilla; LEGNAIOLI, Stefano; TINÉ, Maria Rosaria; DE LUCA, Daphne; MODUGNO, Francesca - Aquazol as binder for retouching paints. An evaluation through analytical pyrolysis and thermal analysis, Polymer Degradation and Stability. Vol. 144, Elsevier, (October 2017), pp. 508-519. Available at: DOI:https://doi.org/10.1016/j. polymdegradstab.2017.09.007 [8 November 2017]. [3] MODUGNO, Francesca; LA NASA, Jacopo; ORSINI, Sibilla; DUCE, Celia; SPEPI, Alessio; TINÉ, Maria Rosaria; UBALDI, Vanessa; DE LUCA, Daphne - Characterization and ageing studies of Aquazol retouching paints using techniques based on Pyrolysis, Poster Session 2: Wednesday 11 May & Thursday 12 May. In Conference Guide and Abstracts, 21st International Symposium on Analytical and Applied Pyrolysis, Pyro 2016, Nancy,

78 Vanessa Ubaldi | Roberto Bestetti | Roberto Franchi | Emanuela Grifoni | Pier Paolo Lottici | Francesca Modugno | Richard Wolbers | Daphne De Luca France, 9-12 May 2016, p. 82, (ConferenceBook). Available at: http://www.pyro2016. com/_media/pyro2016-conference-book.pdf [8 November 2017]. [4] BESTETTI, Roberto; COLOMBO, Annalisa; DE LUCA, Daphne; SELVA BONINO, Valentina E.; UBALDI, Vanessa - L’impiego dell’Aquazol per il ritocco pittorico in Italia: prove preliminari e avanzamento di una sperimentazione, Sessione Poster. In Giornata di Studio e Workshop sull’utilizzo dell’AQUAZOL - AQUAZOL: esperienze ed applicazione nel panorama Italiano, La Venaria Reale (Torino), Italia, 4 giugno 2014. [5] BESTETTI, Roberto; COLOMBO, Annalisa; DE LUCA, Daphne; SELVA BONINO, Valentina E.; UBALDI, Vanessa - Aquazol based retouching colors: Preliminary Tests and Advancement of an Experiment, Poster. In BAILÃO, Ana; HENRIQUES, Frederico; BIDARRA, Ana (Editorial coordinators), RECH2: PROCEEDINGS, 2nd International Meeting on Retouching of Cultural Heritage, Escola Artística e Profissional Árvore, Casa das Artes and Casa Allen, Porto, Portugal, 24-25 October 2014. Available at: https:// www.academia.edu/15993459/RECH2_ Proceedings [8 November 2017]. [6] CHIU, Thomas T.; THILL, Bruce P.; FAIRCHOK, William J. - Poly (2-ethyl-2- oxazoline): A new water and organic soluble adhesive. In GLASS, J. E. - Water Soluble Polymers, Advances in Chemistry. Vol. 213, American Chemical Society, Washington D.C., 1986, pp. 425-433. [7] VAN GELDER, Mark – Aquazol. In METZGER, Catherine A.; MAINES, Christopher; DUNN, Joanna - Painting Conservation Catalog Volume III: Inpainting, Paintings Speciality Group, AIC, 1156 15th St. NW, Suite 320, Washington DC, 2011, pp. 114-129. [8] WOLBERS, Richard C.; MCGYNN, Mary; DUERBECK, Deborah - Poly (2 Ethyl-2- Oxazoline): a new conservation consolidant. In Painted Wood: History and Conservation, Proceedings of the Symposium, Williamsburg, Virginia, 11-14 November 1994, pp. 514-527. [9] LEWIS, Mark; WOLBERS, Richard - Evaluation of the Suitability of Poly (2-ethyl-2- oxazoline) as a Potential Retouching Medium for Easel Paintings. Paper presented at the American Institute of Conservation at the Twenty Third Annual Meeting, June 4-11, St. Paul, Minnesota, 1995, p.76. [10] WOLBERS, Richard - Giornata di Studio e Workshop sull’utilizzo dell’AQUAZOL, La Venaria Reale (Torino), Italia, 4-5-6 giugno 2014. [11] ASBECK, W. K.; VAN LOO, Maurice

The use of aquazol® 500 as a binder for retouching colours: analytical investigations and experiments 79 - Critical Pigment Volume Relationship, Industrial & Engineering Chemistry. Vol. 41, Isseu 7, ACS Publication, (July 1949), pp. 1470- 1475. [12] Out of the three organic self-produced colours and the equivalents QoR®, TGA was performed on only one organic colour, as indicated in the text, because this technique in comparison to the others requires a greater amount of material, which is not available for all the samples, since they were used for other investigations. [13] The third organic pigment Irgazine® Ruby DPP-TR, used to prepare the same selfproduced colour with the Recipes A and B and its corresponding organic colour QoR®, Pyrrole Red Deep, were not analysed with this technique since the colour samples taken were insoluble in the solvents used in liquid chromatography. [14] PELOSI, Claudia; MARABELLI, Maurizio; FALCUCCI, Claudio; GIURLANDA, Flavio; ORTENZI, Floriana; PATRIZI, Francesca - Problematiche conservative degli acquerelli nel restauro. Archeomatica, numero 0, Novembre 2009, pp. 24 -27.

Abstract The field of art conservation has used Polyvinyl acetate PVAC for consolidation and retouching since the 1930s. Its use as a retouching medium was first mentioned in a 1935 journal, Technical Studies in the Field of the Fine Arts, published from 1932-42 by the Fogg Art Museum. PVAC paints were found to exhibit little or no discoloration upon aging, could be dissolved in a range of solvents including alcohols, glycol ethers, acetone, and toluene, and could maintain both clarity and reversibility.  Hoescht Mowilith 20 and Union Carbide AYAB were the typical PVAC resins used for inpainting. Collaboration between Golden Artists Colors and painting conservators led to the introduction of Golden’s pre-made PVAC conservation paints based on a blend of Union Carbide AYAA and AYAC in 1991. Mark Golden also created custom-made retouching paints for the 1988-1992 treatment of Whistler’s Peacock Room in the Freer Gallery of Art. Unfortunately, both the Mowilith and Union Carbide resins were discontinued causing Golden to cease production of the line in 2010. Continued interest in PVAC retouching paints inspired Golden to collaborate with conservators and conservation scientists to reformulate a new conservation PVAC RETOUCHING COLORS: A BRIEF HISTORY AND INTRODUCTION TO GOLDEN’S NEWLY FORMULATED PVA CONSERVATION COLORS Kristin deGhetaldi (1) | Brian Baade (1) | Joyce Hill Stoner (1) | Jim Hayes (2) | Samantha Alderson (3) 1. University of Delaware, 18 E. Main St. Old College room 302, Newark, DE, 19716; [email protected]; [email protected]; [email protected] 2. Golden Artists Colors, Inc.188 Bell Road New Berlin, NY 13411; [email protected] 3. American Museum of Natural History, 79th St. and Central Park West, New York, NY 10024; [email protected]

1. INTRODUCTION PVAC resins have been used as a retouching medium in the field of conservation since 1935[1]. In 1991, Golden Artists Colors, Inc. introduced a line of specially formulated PVAC conservation paints based on a mixture of AYAA and AYAC manufactured by the Union Carbide Corporation[2]. However, nearly a decade later, the Union Carbide discontinued the production of the PVAC AY resins and Golden ultimately halted production of their PVA Conservation Colors by 2010. paint line three years later. After much testing, the company was once again able to provide conservators with premade PVAC conservation paints in 2017. This talk will briefly outline the history of PVAC retouching paints and discuss some of the specific properties of the new Golden line including molecular weight, gloss, solubility, and practical application tips with examples from the authors’ personal conservation treatments. Keywords PVAC; Polyvinyl acetate resin; Inpainting; Retouching; Golden PVA colors; Golden Artists Colors, Inc.; AYAA; AYAC While conservators have continued to use leftover reserves of the AY resin line for retouching purposes, the pre-made PVA Conservation Colors offered some distinct benefits. In 2013, a renewed collaboration began between conservators, scientists, and Golden Artists Colors, Inc. to re-create the PVAC retouching paints. Thanks to ongoing research spearheaded by objects conservator Samantha Alderson, efforts were already underway to identify and evaluate viable replacements for some of the discontinued AY resins. Paintings conservators from the University of Delaware contacted Alderson and subsequently reached out to Golden Artists Colors to explore the possibility of re-creating a new line of PVAC retouching paints for the art conservation field. This paper will outline some of the preliminary analytical results from tests performed on the replacement PVAC resin. In addition, practical working characteristics of the retouching paints will be summarized based on the treatment of a 17th-century oil on canvas painting attributed to Pietro da Cortona and his workshop. 1.1. Historical Use of PVAC Conservation Paints In 1935, PVAC homopolymer resins were first tested as a potential medium for retouching by conservation scientist Rutherford John Gettens [1]. These initial tests, performed at the Fogg Art Museum, were presumably inspired in part by an article published in a conservation journal earlier that year which focused on the use of polyvinyl acetate in artists’ paints [3]. By the 1950s, PVAC resin was being used routinely as a retouching medium, both as a watermiscible emulsion as well as a simple solution binder that could be thinned with organic solvents [4]. In 1959, conservation scientist Robert L. Feller and paintings conservator Mario Modestini began testing a range of PVAC resins at the National Gallery of Art in Washington, ultimately identifying Union Carbide’s AYAB resin as possessing the most desirable working properties [5, 6, 7]. As the glass transition temperature of AYAB was

82 Kristin deGhetaldi | Brian Baade | Joyce Hill Stoner | Jim Hayes | Samantha Alderson fairly low (remaining somewhat tacky at room temperature), Modestini would often interlayer resins with higher glass transition temperatures (e.g. Paraloid B-72) throughout the inpainting process to effectively seal areas containing PVA retouching and prevent the accumulation of dust [6, 7]. In subsequent decades PVAC resin gained popularity as a retouching medium throughout the conservation community. By the 1980s, however, Union Carbide was no longer producing AYAB, prompting scientists and conservators to identify a replacement material. Conservation scientist René de la Rie, then head of the Scientific Research Department at the National Gallery of Art, suggested that conservators consider using a PVAC resin manufactured by the German company Hoechst. Mowilith 20 possessed a viscosity and refractive index close to that of AYAB (RI=1.467) [ 7, 8]. While some conservators continued to mix dry pigments with Mowilith 20 or with leftover reserves of the discontinued AYAB resin, other paintings conservators expressed interest in obtaining premade retouching colors bound in PVAC resin. Golden began testing a 50/50 mixture of AYAC (lower molecular weight than AYAB) and AYAA (higher molecular weight than AYAB) and the mixture was found to possess satisfactory working and aging properties. A set of colors bound in this mixture was provided to paintings conservators Wendy Samet and Dr. Joyce Hill Stoner for their treatment of James McNeil Whistler’s Peacock Room at the Smithsonian Institution’s Freer Gallery of Art in Washington DC (the treatment occurred between 1988-1992) and in 1991, Golden PVA Conservation Colors became officially available for purchase [2]. Nearly a decade later, Samantha Alderson, objects conservator at the American Museum of Natural History, learned that the Union Carbide AY resins (AYAC, AYAA, AYAF, AYAT) had been discontinued and that Hoechst’s Mowilith 20 was no longer being manufactured. Additionally, she learned that that some PVAC substitutes available through certain art conservation suppliers were mislabeled [9, 10]. Consequently, Golden discontinued their PVA Conservation colors by 2010 as a replacement resin had not yet been identified. 1.2 Recent Developments in PVAC Paints Used in Conservation The PVAC resins that have been commonly used for retouching purposes have not been produced for nearly a decade. As other PVAC resins from Union Carbide’s AY line have also become popular for other uses in conservation (e.g. as surface coatings, consolidants, etc.), a collaborative project was begun by Alderson and her colleagues to identify potential substitutes for these resins, the results of which will be presented in a forthcoming publication [11]. They began by collecting samples of PVAC resin in a wide range of molecular weights from several current manufacturers. These were evaluated and compared to samples of the discontinued Union Carbide and Hoescht resins. The team used a variety of analytical instruments to evaluate and test the potential resins including Fourier Transform Infrared Spectroscopy (FTIR) to characterize chemical composition and Gel Permeation Chromotagraphy (GPC) to measure the molecular weight. In 2013, Alderson was contacted by Kristin deGhetaldi, a paintings conservator, about possible replacement resins for the reformulation of the Golden PVA Conservation Colors. DeGhetaldi had been contracted to conserve a large 12-by-20 foot oil-on-canvas painting attributed to Pietro da Cortona in collaboration with fellow paintings conservator Brian Baade. Rather than trying to replicate the

PVAC Retouching Colors: A brief history and introduction to GOLDEN’s newly formulated PVA Conservation Colors 83 original 50/50 mixture of two PVAC resins of different molecular weight, Alderson suggested initially testing single resins as replacements. She provided Jim Hayes, the technical director at Golden Artists Colors, Inc., with five samples of resins that seemed to be promising substitutes for the original mixture as well as old samples of AYAA and AYAC for comparative testing. 2. MATERIALS AND METHODS 2.1 Mechanical, Solubility, and Color/Gloss Testing Golden’s technical staff produced five paint samples based on the potential resin replacements identified by Alderson and her colleagues in addition to re-creating the original 1:1 AYAA/AYAC mixture for comparison. Each of the five resins as well as the 1:1 AYAA/AYAC mixture (designated as the control) were mixed with three pigments: titanium white (PW6), quinacridone red (mixture of PR 206 and PR 202), and raw umber (PBr7). Paint drawdowns (10 mL) were created and then subjected to a series of tests before and after shortterm light aging. Artificial aging was performed under ambient conditions using a filtered Xenon arc-source with a radiant exposure of 510 kJ/m2 at 340 nm for a period of 405 hours. To assess changes in gloss, a BYK Micro-TRI-Gloss Meter was used on all paint samples (readings were obtained at 60 degrees). Resolubility was assessed by applying cotton swabs saturated in denatured alcohol to the surface of the aged paints, and the number of circles were recorded before the swabs effectively broke through the surface of the paint samples. Flexibility was assessed by manually manipulating the substrate (acrylic-primed canvas) in order to observe any potential cracking, flaking, or delamination. Finally, a Xrite CI7800 Benchtop Color Spectrophotometer was used to monitor any potential shifts in color (calculated using the CIELab delta E masstones). 2.2 Gel Permeation Chromatography (GPC) Gel Permeation Chromatography (GPC) was performed on four pigmented samples bound in the final selected resin: Prussian Blue (PB 15:1/PV 23/PBk 9), Titanium White (PW6), Yellow Ochre (PY43), and Burnt Umber (PBr7). All four samples were prepared by adding 1.5 mL of tetrahydrofuran to approximately 10- 20 mg of paint. After centrifuging the samples for 30 seconds, the dissolved resin was obtained from each of the samples using a 220 nm filter. 5 µl of each samples was then injected into a Waters Alliance® System 2695 Separations Module equipped with a Waters 2414 Refractive Index Detector using a 300x7.8mm High Speed GPC Column (25 minutes @ 35 deg C). Results were interpreted using Millenium® 32 Chromatography Manager Software. 3. RESULTS AND DISCUSSION Golden prepared all five of the samples and sent them to painting conservators deGhetaldi, Baade, and Stoner to perform a series of blind tests to determine which had the most appropriate working properties (the paints were labelled with a code so that the conservators would not know which resin they were using). The conservators unanimously concluded that they could not tell the difference between the workability and re-solubility of the five samples from that of the original Golden PVA Conservation Colors (1:1 AYAA/ AYAC). With the analytical and empirical testing completed, Alderson suggested that Golden select Vinavil Raviflex BL5S as their PVAC binder as her research found that this resin possessed physical properties that were most like Mowilith 20 [11].

84 Kristin deGhetaldi | Brian Baade | Joyce Hill Stoner | Jim Hayes | Samantha Alderson 3.1 Mechanical, Solubility, and Color/ Gloss Test Results Golden’s initial tests on Vinavil Raviflex BL5S have yielded promising results when compared to the control (1:1 AYAA/ AYAC). It showed minimal differences from the control when subjected to the same series of tests (see Tables 1A and 1B) both before and after shortterm aging. The Vinvavil Raviflex BL5S even slightly outperformed the control on some tests. For example, the delta E values measured for each of the new PVAC colors before and after light aging were all below one (not discernible to the human eye). Very minimal changes in re-solubliity were also observed, an expected outcome as PVAC resins have shown little to no signs of cross-linking over time. 3.2 GPC Molecular Weight Results Five samples were subjected to GPC analysis in order to confirm the molecular weight distribution that has been reported in the literature and by the relevant manufacturer (see Figure 1). Samples of AYAF, AYAA, and AYAC were chosen as they span a wide molecular weight range and the latter two resins were used as the primary binders for Golden’s previous PVA line. Two paint samples were also run: burnt umber (PBr7) bound in 1:1 AYAA/ AYAC and cadmium red light (PR 108) bound in Vinavil Raviflex BL5S. As some of the samples did not generate narrow distributed single peaks, only an approximation of Vinvavil’s molecular weight could be calculated. Based on the logarithmic relationship between the elution time and molecular weight, the weight average molecular (as opposed to the number average molecular) was calculated to be approximately 33,000 PIGMENT BINDER GLOSS (BEFORE XENON AGING) GLOSS (AFTER XENON AGING) INITIAL FLEXIBILITY FLEXIBILITY (AFTER XENON AGING) Titanium White Control (1:1 AYAA/AYAC) 26 24 control 0.4 Vinavil Raviflex BL5S 48 46 Slightly less 0.57 Quina-cridone Crimson Control (1:1 AYAA/AYAC) 24 34 control 1.05 Vinavil Raviflex BL5S 32 34 Slightly more flexible 0.97 Raw Umber Control (1:1 AYAA/AYAC) 5 5.4 control 0.5 Vinavil Raviflex BL5S 8.1 10.3 Slightly more flexible 0.76 Table 1A • Chart summarizing test results relating to gloss and flexibility of PVA paints before and after short-term aging. PIGMENT BINDER INITIAL RESOLUBILITY RESOLUBILITY (AFTER XENON AGING) CIELAB, ∆E, MASSTONES (AFTER XENON AGING) Titanium White Control (1:1 AYAA/AYAC) 27 45 0.4 Vinavil Raviflex BL5S 22 29 0.57 Quinacri -done Crimson Control (1:1 AYAA/AYAC) 40 54 1.05 Vinavil Raviflex BL5S 25 28 0.97 Raw Umber Control (1:1 AYAA/AYAC) 42 45 0.5 Vinavil Raviflex BL5S 37 39 0.76 Table 1B • Chart summarizing test results relating to resolubility and color change of PVA paints before and after short-term aging.

PVAC Retouching Colors: A brief history and introduction to GOLDEN’s newly formulated PVA Conservation Colors 85 amu. When comparing this value to the reported molecular weight range (22,000-30,000 amu), this falls in line with the trend observed for all three AY resins, as AYAF, AYAA, and AYAC all possess weight average molecular values that are greater than their number average molecular values [8, 12]. Additional testing using GPC and Size Exclusion Chromatography (SEC) will likely reveal more precise approximations for both the weight average molecular and number average molecular values. 3.3 Working Properties of PVAC Retouching Paints Like the earlier PVAC AY resins, the new line of Golden PVA Conservation colors (made with the replacement resin Vinavil Raviflex BL5S) can be dissolved for retouching purposes using alcohols. To slow down the evaporation rate (allowing for more blending and richer glazes), a small amount of ethylene glycol or propylene glycol monomethyl ether (e.g. Arcosolv PM) can be added to the alcohol diluent. To achieve a more matte appearance, the PVA colors can be further thinned with alcohols (e.g. ethanol) or mixed with additions of dry pigment and/ or matting agents (e.g. glass microballoons). Conversely, a thicker and/ or more glossy paint consistency can be achieved by increasing the amount of ethylene glycol/ propylene glycol monomethyl ether. Additions of the pure resin (Vinavil Raviflex BL5S) predissolved in an alcohol, a mixture of alcohol and ethylene glycol/propylene glycol monomethyl ether, or pure ethylene glycol/ propylene glycol monomethyl ether can be added to the paint. All of these factors can be controlled to achieve the desired level of gloss and open working time. One advantage of using the pre-made PVAC conservation paints is that the colors are well and evenly dispersed. One challenge that faces conservators who hand-mixing dry pigments into a fast-setting resinous medium is to create a paint that will not “sink” over time, a phenomenon due in part to poor pigment dispersion. One potential drawback to all PVA retouching paints is the low refractive index of the resin (1.4665). This is easily remedied by the superimposition of a glaze containing a higher refractive index (e.g. Laropal A81) or the application of a surface varnish with similar properties. PVAC resins are polar by nature and therefore do not wet well onto pigments that are non-polar such as carbon black [13]. One solution to counteract this problem is to add minute amounts of alcohol soluble dyes (e.g. Orasol® Dyes) that have satisfactory lightfast ratings; however, the dyes should be used sparingly and preventive measures (e.g. coating with a varnish containing UV Light Stabilizers, employing appropriate lighting conditions) should be considered if dyes are added to the paints. This particular method (using the newly formulated PVA paints) was used to reintegrate large sections of paint loss on The Triumph of David in order to achieve a satisfactory degree of saturation in darker passages (Figure 2). Like some of the AY resins, the glass transition temperature of the resin in the new PVAC paints is close to room temperature (the manufacturer recommends storing the pure resin at a temperature above 20 degrees C). Consequently, it is advisable to coat the retouching paints with an appropriate varnish layer possessing a higher glass Figure 1 • Comparison of chromatograms collected using GPC associated with AYAF, AYAA, AYAC and original and new PVA paint samples.

86 Kristin deGhetaldi | Brian Baade | Joyce Hill Stoner | Jim Hayes | Samantha Alderson transition temperature in order to avoid the potential accumulation of dust/grime (although this is likely only to affect areas that are covered with thick applications of the paints) [12]. For removal of the paints, ethanol can be used; however, if the artwork is sensitive to alcohols, toluene has been successfully used to remove PVAC resins after short and long-term aging. 4. CONCLUSIONS Previous research and studies have shown that PVAC resins are an appropriate option for making paints for use in inpainting. PVAC resins have been shown to exhibit little or no discoloration upon aging, are soluble in a wide range of solvents, and maintain both clarity and reversibility. The loss of earlier sources of such a resin prompted the discontinuation of Golden PVA Conservation Colors. Research began to find a new replacement resin, which would possess similar or superior properties and allow Golden to resume the production of pre-made PVAC conservations paints. Extensive testing by scientists and conservators resulted in the selection of Vinvavil Raviflex BL5S as a replacement resin. Golden Artists Colors has relaunched their PVA Conservation Colors and they are now available to conservators. ACKNOWLEDGMENTS The authors would like to acknowledge Rachel Modrovsky for her assistance with the preliminary tests performed on the Vinavil Raviflex BL5S paints. We are also indebted to Dr. Shuang Liu for performing Gel Permeation Chromatography on the Figure 2 • Before (left) and after (right) retouching large area of loss in The Triumph of David attributed to Pietro da Cortona using the newly formulated Golden PVA Paints combined with Orasol Dyes (photo courtesy of Villanova University).

PVAC Retouching Colors: A brief history and introduction to GOLDEN’s newly formulated PVA Conservation Colors 87 PVA samples at the Microscopy and Mechanical Testing (MMT) Center at the University of Delaware. REFERENCES [1] GETTENS, Rutherford J. - Polymerized vinyl acetate and related compounds in the restoration of objects of art. Technical Studies in the Field of Fine Arts. Vol. 4, no. 1 (1935), pp. 15–27. [2] STONER, Joyce Hill. - America’s colormen: Bocour, Levison, Gamblin, and Golden. In Modern Art, New Museums: Contributions to the Bilbao Congress, 13–17 September 2004. London: International Institute for Conservation, 2004. pp. 189–192. [3] CLARKE, William J.; IVES, Herbet Eugene - The use of polymerized vinyl acetate as an artist’s medium. Technical Studies in the Field of Fine Arts. Vol. 4, no. 2 (1935), p.4. [4] DIGNEY-PEER, Shawn, et al. The imitative retouching of easel paintings. In STONER, Joyce H.; RUSHFIELD, Rebecca A., eds. – The Conservation of Easel Paintings. London: Routledge, Taylor & Francis Group, 2012. pp. 607-634. [5] FELLER, R. - Exposure Tests on Traditional and Polyvinylacetate Retouching Systems and Characterization of Certain Modern Proprietary Painting Media. AIC Preprints, Fourth Annual Meeting, Dearborn, Michigan, 1976, p. 126. [6] BERGER, Gustav Adolf. - Inpainting using PVA medium. In Cleaning, Retouching and Coatings: Technology and Practice for Easel Paintings and Polychrome Sculpture, Preprints of the Contributions to the Brussels Congress, 3–7 September 1990. London: International Institute for Conservation, 1990, pp. 150-155. [7] BERGER, Gustav Adolf. - Inpainting using PVA medium – Inpainting using PVA Medium: Mario Modestini’s Pioneering Research – In BERGER, Gustav Adolf; RUSSELL, William H. ed. - Conservation of Paintings: Research and Innovations. London: Archetype Publications., Ltd., 2000. pp. 191–216. [8] UNION CARBIDE. - Polyvinyl acetate resins for coatings and adhesives. Danbury, CT: Union Carbide Chemicals and Plastics Company Inc., 1989. [9] ALDERSON, S. - Union Carbide no longer manufacturing PVAC resins. AIC News Vol. 34, no. 2 (2009), pp. 16–17. [10] ALDERSON, S. - Response to Supplier for AYAA Sought, Conservation DistList. Available at: http://www.cool.conservation-us.org/ byform/mailing-lists/cdl/2013/0918.html (12 July, 2017). [11] ALDERSON, S., DOWN, J.L., MAINES, C.S., WILLIAMS, R.S., and YOUNG, G.R. - Substitutes for discontinued poly(vinyl acetate) resins used in conservation (forthcoming publication in the Journal of the American Institute for Conservation). [12] VINAVIL - Technical data sheet. Raviflex BL 5S. Available at: http://www.vinavil.com/ public/1/SchedeTecniche/raviflex%20bl%20 5s%20-%20a%20(engl).pdf (12 July, 2017). [13] DIGNEY-PEER, S., THOMAS, K., PERRY, R., TOWNSEND, J., and GRITT, S. - The imitative retouching of easel paintings. In STONER, Joyce H.; RUSHFIELD, Rebecca A., eds. – The Conservation of Easel Paintings. London: Routledge, Taylor & Francis Group, 2012. pp. 607-634.

Abstract The aim of this work is to present preliminary results of the use of watercolour markers in chromatic reintegration. The behaviour of 15 watercolours of Winsor & Newton® markers were tested to ascertain whether these are useful for use in the retouching practice. Three different types of reintegration techniques were used to test the two brush tips: mimetic, pointillist and tratteggio, and three testing surfaces were created by applying four fillers over a wooden board covered by calcium carbonate and rabbit glue, Modostuc® and Gesso Primer. To examine the process of the reintegration of the markers on the surfaces an USB digital microscope was used to visually assess its details and a hyperspectral imaging system was used to assess its chromatic properties. It was found that the used fillers and accompanying varnish USING WATERCOLOUR MARKERS IN CHROMATIC REINTEGRATION Liliana Cardeira (1, 4) | Ana Bailão (1, 2, 3) | João Linhares (3) | Sérgio Nascimento (3) 1. Faculty of Fine Arts, University of Lisbon; Largo da Academia Nacional de Belas Artes nº 14, 1200-005, Lisboa; E-mail address: [email protected]; 2. Research Center for Science and technology of the Arts - Portuguese Catholic University, Centre Regional of Porto, CITAR, Portugal; Rua Diogo de Botelho 1327, 4169-005, Porto; E-mail address: [email protected]; 3. Centre of Physics, University of Minho, Gualtar Campus, Gualtar, 4710-057, Braga, Portugal; E-mail address: [email protected]; 4. HERCULES Lab and Chemistry Department, Evora University, Portugal ;Palácio do Vimioso Largo Marquês de Marialva, nº8, 7000-809, Évora; smcn@[email protected]

1. INTRODUCTION The use of colour markers is well known in the field of the artistic materials, but their use in the context of the chromatic reintegration on conservation and restoration is still unknown. The purpose of this project was to present preliminary results of the assessment of the use of watercolour markers in chromatic reintegration. The watercolour markers were tested under several conditions of technique of use onto several surfaces to ascertain whether they can be used on the retouching practice [1, 2]. produces a non-neglected visual difference in the obtained colours, when markers are used to reintegrate art paintings. These findings seem to indicate that the watercolour markers can be used during the process of reintegration, but the fillers and varnish in use has to be taken into account. Keywords Watercolour markers; Fillers; Varnish; Chromatic reintegration techniques. The study is being conducted within the framework of the conservation and restoration of a set of paintings by Adriano de Sousa Lopes (1879-1944) [3]. This artwork belongs to the painting collection of the Faculty of Fine Arts, University of Lisbon (FBAUL), Portugal. Researching the sustainability of use of retouching materials remains a priority in the 21th century in the context of restoration. The watercolour is a widely used and studied material in chromatic reintegration [4]. There are several watercolour brands available, used by professional conservators that can be found in common retailer, and it is possible to find watercolours in a wide variety of forms: pans, tubes, crayons, coloured pencils, even stones. Nevertheless the wide availability of watercolours, their usage as an option of chromatic integration in restoration is yet to be assessed systematically. The purpose of this work was to assess the usage of watercolour markers in the context of the conservation and restoration of art paintings and systematically assess its behaviour under different fillers and varnishes. 2. MATERIALS AND METHODS To assess the use of watercolour markers of W&N [5] (Figure 1) in the chromatic reintegration of art paintings, watercolour markers were tested on three different types of fillers using different reintegration techniques. This assessment was done two-fold. Under visual inspection of the chromatic properties, enlarged by the usage of a digital microscope, and by the means of a hyperspectral imaging system. The chromatic properties of the object under analysis were compared. Recently, watercolours in the form of a pen became available. To conduct the experiments the Winsor and Newton® watercolour markers (Table 1) were used. They are much cheaper than their alcohol based version but non-refillable. Nevertheless, these watercolour markers enable the spread of its Figure 1 •Watercolours in pens –form from the Winsor & Newton Company. Liliana Cardeira©.

90 Liliana Cardeira | Ana Bailão | João Linhares | Sergio Nascimento colours without the need of a brush or water. According to the manufacturer the colour blending varies depending on the paper or substrate used so it is paramount to test the markers over different fillers to assess their behaviour. It was decided to test the markers with three fillers and four varnishes to check is functionality and to test their influence on the final colour saturation. COLOUR NUMBER PIGMENT LIGHTFASTNESS ASTM 4303 119 – Cadmium yellow pale hue PY74 -------- 266 – Gamboge hue PY83 -------- 552 – Raw Sienna PY42, PY83, PR179 -------- 554 – Raw Umber PY83, PV23 -------- 074 – Burnt Sienna PR101 I 076 – Burnt umber PY83, PR122, PBk7, PBr7 -------- 061 – Burnt red PR188, PY83, PV23 I 95 – Cadmium red hue PR188 II 545 – Quinacridrone Magenta PR122 -------- 522 – Phthalo green PG7 I 312 – Hooker’s green Dark PB15:3, PY83 -------- 514 – Phthalo blue (red shade) PB15:2 II 515 - Phthalo blue (Green shade) PB15:3 II 337 – Lamp black PBk7 I 331 – Ivory black PBk7, PY83, PBk9 -------- Mock-ups with different fillers were created to compare the behaviour of 15 colours from the watercolour markers of Winsor & Newton® (as described in Table1). The fillers were applied over a wooden board with dimensions of 30cm x 23cm, and were made from: calcium carbonate and rabbit glue from CTS; Modostuc® from Plasveroi International; and Gesso Primer from Talens®. Over the watercolours four varnishes were applied: Paraloid B72®, Laropal 81®, Retouching varnish of Talens® and retouching varnish of W&N®. Each one of the 15 watercolour markers were tested on each one of the three fillers, each one under one of the four varnish used, on a combination of 12 conditions per colour. Each colour combination was then assessed under a visual inspection and the hyperspectral system. To extend the analysis of the chromatic reintegration, three different reintegration techniques were used and evaluated. 2.1. Visual inspection of the chromatic reintegration techniques with the watercolour markers. The markers in pen-form have the advantage of having a fine point at one end and a flexible brush tip on the other for fine or thick strokes, respectively. The fine tip has a more accurate trace but thicker and the brush tip allows the application of colour layers. Some of these materials have a lightfast and are highly pigmented such as Burnt Sienna, Burnt red, Cadmium red hue, Phthalo green, Phthalo blue (red shade), Phthalo blue (Green shade) and Lamp black. In the context of this research, different types of reintegration techniques were used to test the fine tip and the flexible Table 1 • Pigments, references of watercolour markers and American Society for Testing Material (ASTM) [6]. Liliana Cardeira®.

Using watercolour markers in chomatic reintegration 91 brush tips, namely, mimetic, pointillist, Tratteggio and Selezione cromatica [4]. Figure 2 represents the different reintegration techniques over different fillers. No varnish was used in this case. Care was taken to reproduce the same pattern and painting technique over the different fillers. Understanding now the colours react and interact on the distinct reintegration technique is key to validate the process of the selection of the proper chromatic reintegration technique in each case. To asses this reaction and interaction of the colours over the fillers a visual inspection was made. The behaviour of the watercolour markers over three fillers using different reintegration techniques was made by using an USB digital microscope Dino-Lite Pro brand - AM4013-FVW model with 1.3 Mpixel resolution. This microscope is portable, equipped with one switchable LED UV light and enabled an augmentation of the image viewed by 200x times. This technique was used to verify in detail the behaviour of the material in the distinct types of fillers, as the magnification using the USB microscope enable a better visual comparison. The easy of the colour spread, the simple of colour application, and the adsorption of the watercolour paint by the substrate material were observed and analysed in order to estimate the best reintegration technique over the better ground layer. About the methodology, it was only used the digital microscope Dino-Lite for observation of the samples, but in this case all samples were assessed by the same experienced observer and as such the results should be accepted, even if small differences are to be assumed. 2.2. Inspection hyperspectral of the chromatic reintegration technique with the watercolour markers. To understand the chromatic properties of the watercolour markers Figure 2 • Tests of markers in three types of fillers with different reintegration techniques. Liliana Cardeira and Ana Bailão®. Figure 3 • Markers under different fillers and distinct varnishes. Anabela Cardeira, Carina Carvalho and Liliana Cardeira®.

92 Liliana Cardeira | Ana Bailão | João Linhares | Sergio Nascimento under different varnishes (Paraloid B72®, Laropal 81®, using retouching varnish of Talens® and retouching varnish of W&N®) and fillers (calcium carbonate, Modostuc® and Gesso Primary) (as represented in Figure 3 and Table 1) the mock-ups were digitized with a hyperspectral imaging system to obtain their spectral information combined with their spatial information. [7] The hyperspectral imaging system was comprised by a fast-tuneable liquid-crystal filter coupled with a monochromatic digital camera and a zoom lens. The acquisition was carried from 400 nm to 720 nm in 10 nm steps, with a spatial resolution of 1344 (H) x 1024(V) pixels with a field of view of about 7º x 5º. More information about the system can be found elsewhere [8]. The hyperspectral data was calibrated using the spectrum of the light reflected from a flat uniform reference present in the scene during the process of image acquisition. The spectral reflectance of each pixel of the image was corrected for dark noise, spatial non-uniformities and stray light. The spectral radiance of each image pixel was then estimated from the reflectance data assuming the CIE D65 standard illuminant [9] and converted into the CIELAB colour space coordinates assuming the CIE 1931 standard colorimetric observer [10,11]. The CIELAB coordinates [11] were averaged across a fixed area over all the combinations of watercolour markers, different fillers and varnishes, and then compared. By taking mockup 1 as represented in Figure 3 as an example, using the first yellow marker under Paraloid B72 as reference, the colour difference was estimated against the other three varnishes and averaged. In all cases, the colours under Paraloid B72 were used as reference. The averaged area included 45 pixels horizontally and 10 pixels vertically, with an approximated area of 7813 mm2 . The standard deviation was also estimated as a measure of the computed uncertainty. To estimate the variations in colour induced by the three fillers and varnishes for the same watercolour marker, the colour difference between one of the possible combinations onto the others was estimated by computing the Euclidean Distance between the two pairs of colours in the CIELAB colour space by: CIELAB colour space provides a numerical representation of the visual chromatic perception. As such, by estimating a numerical distance in such three-dimensional space by using the former equation, a visual chromatic difference is directly related [9, 12]. Only using hyperspectral images is it possible to have access to both the spatial and spectral information over Figure 4 • Spectral imaging setup for the mock-up acquisition (Left) and the hyperspectral imaging system (right), João Linhares and Sérgio Nascimento®.

Using watercolour markers in chomatic reintegration 93 such wide areas. Figure 4 represents the process of image acquisition using the hyperspectral imaging system. 3. RESULTS AND DISCUSSION As shown in Table 2, the watercolour markers can be used in all the tested reintegration techniques, but sometimes the fillers do not produce the desired outcome. According with the observations with the digital microscope Dino-Lite, about the colour spread, the colour application, the adsorption of the watercolour paint by the substrate material and the capability of gradually building up the colour using multiple layers, with the last layer not affecting the bottom layer, the most suitable reintegration technique was the pointillism. The filler with best results was the calcium carbonate. Table 2 presents a summary of the authors findings when experimenting the three reintegration techniques over the three fillers. The dots, when observed with the Dino-Lite microscope, were only uniform and round over calcium Figure 5 • Images of mimetic, pontilhism, tratteggio technique obtained with a USB digital microscope Dino-Lite Pro brand - AM4013-FVW model with 1.3 Mpixel resolution. Ana Bailão®. MIMETIC POINTILLISM TRATTEGGIO Gesso Primer In the application of colour, this spreads Easy application in 1st and 2nd layer In the application of the 3rd and 4th layer begins to create textures Easy application Uniform points in the 1st and 2nd layer Easy control Less saturation and less porous Traces become thinner Calcium carbonate In the application of colour, this spreads Easy application in 1st and 2nd layer In the application of the 3rd layer begins to create textures Easy application It allows you to create burnish Uniform points in the 1st and 2nd layer It allows you to create fine traits Modostuc Colour application, very difficult Easy application It is stained due to the porosity of the mass In the 2nd tier points are spreading Thick strokes and difficult to be controlled Features spread Greater absorption, influencing trace and colour saturation Table 2 • Results found between different types of fillers with different types of chromatic reintegration techniques. Liliana Cardeira and Ana Bailão®.

94 Liliana Cardeira | Ana Bailão | João Linhares | Sergio Nascimento carbonate. With Modostuc® the dots adopt an irregular round shape. It was also difficult to apply a flat and regular layer of colour over Modostuc® and Gesso Primer. (Figure 5). The deformation of the points and the influence of the fillers were examined at magnifications of 200X. As can be seen in Figure 6, the pointillist technique had a different behaviour depending on the fillers of the ground layer. These results seems to support that the best reintegration technique is the pointillism over the calcium carbonate filler. Using the hyperspectral imaging it was found that there was a great visual impact of the filler and varnish over the perceived colour of the watercolour marker (Table 3). The average colour difference estimated using the CIELAB Euclidian distance was of 4.8 (±2.6), 5.8 (±2.7) and 7.1 (±3.3) to mock-up 1, 2 and 3, respectively, and considering only the chromatic changes, discarding the luminance information, the results obtained were 3.9 (±2.4), 5.3 (±3.0) and 5.7 (±3.7), for mock-up 1, 2 and 3, respectively. This was estimated by averaging the chromatic coordinates of an area of equal size across each filler and varnish combination, and by using the colour ∆Eab formula as described in the Materials and Methods Section. Having the same filler and the same marker it was possible to assess the colour changes across different varnishes. It was found that, the uniformity of the marker was visually recognizable and quantified by the estimated colour differences with values higher than the expected threshold for complex images (DE of 2.2 [13]). This was found by comparing all the possible combinations of fillers and varnishes and estimating the colour differences higher than the 2.2 threshold limit of discrimination. It was assumed that if the colour difference was higher than the threshold, the samples were visibly different. With this technique it was possible to register a very significant change in sienna burnt, hooker’s green dark, blue Phthalo (green shade) and raw sienna in mock-ups 2 (Gesso Primer) and 3 (Modostuc®). However, mock-up 1 (Calcium carbonate) presents very stable pigments: cadmium red hue, sienna burnt, burnt red and Phthalo Blue (red shade). The change of varnish depends on the fillers. In mock-ups 1 and 2, it is possible to see the colour Figure 6 • Results with microscope Dino-Lite in various fillers with the pointillist technique, for magnifications of 200X. Liliana Cardeira®. COLOUR LUMINACE CALCIUM CARBONATE 4.8 3.9 MODOSTUC® 7.1 5.7 GESSO PRIMARY 5.8 5.3 Table 3 • Results of the average colour difference and luminace. João Linhares®.

Using watercolour markers in chomatic reintegration 95 change with the varnish Talens® while in sample 3, it is the varnish Laropal 81® that it is more accentuated. 4. CONCLUSIONS It was found that the used fillers and accompanying varnish produces a non-neglected visual difference in the obtained colours, when markers are used to reintegrate art paintings. It was found that the fine point enabled conservators to achieve more control when performing the distinctive retouching, especially using the pointillism technique. It was also found that the fillers influenced the brushstroke of the markers and the saturation of the colours. The flexible brush likewise allowed for uniform underpainting, more saturated in porous fillers, like Modostuc®. These markers were highly pigmented and since they were water-based they provided a permanent ink flow. This characteristic was good for pointillism but did not allow blending or the creation of hues gradation when more than one layer was needed. The tests proved that it was possible to use watercolour markers during the process of reintegration, especially when working with small chromatic losses to be reintegrated with saturated colours. The selection of the markers according to the pigment, filler and varnish has to be done first, as the colour differences demonstrate, since the colour changes between the same water marker colour, on the same filler but under diverse varnish was greater than the threshold of the colour difference detection for complex scenes. This material doesn´t need watering in pigment, and ends up generating a faster and cost-effective process. The hyperspectral system has the advantage of good spatial resolution, as good as the human eye at the same distance of viewing, nevertheless the colour space used to perform the estimations of the colour differences is known not to be perfectly uniform (see reference [13]), nevertheless since this is a comparative study, the results can be used and compared among each other. REFERENCES Scientific article: [1] Cardeira, L.; Bailão, A.; Baptista Pereira, F.; A ., Candeias, A.; Nascimento, S.; Linhares, J. – Using watercolours markers in chromatic reintegration: a case study. 5th International Conference, YOuth in Conservation of Cultural Heritage, YOCOU 2016. [2 (4)] BAILÃO, A. - Critérios de intervenção e estratégias para a avaliação da qualidade da reintegração cromática em pintura. Porto, Universidade Católica Portuguesa (2015): pp.250-256. [3] CARDEIRA, Liliana - Conservação e Restauro das obras do pintor Adriano de Sousa Lopes da Colecção de Pintura da FBAUL. FBAUL,

96 Liliana Cardeira | Ana Bailão | João Linhares | Sergio Nascimento Dissertação de Mestrado, (2014). [4] BAILÃO, A. - As técnicas de Reintegração Cromática na pintura: revisão historiográfica. Espanha, Ge-conservacion, nº 2 (2011): pp. 45-63. [7] SÁNCHEZ ORTIZ, A. et all. “Investigación sobre la estabilidad química y óptica de materiais contemporáneos para reintegración cromática”. In IV congreso del GEIIC, Cáceres, 2009. Cáceres: GEIIC (2010): pp. 195-205. [8] PINTO, P.D., LINHARES, J.M.M., NASCIMENTO, S.M.C. “Correlated Colour temperature preferred by observers for illumination of artistic paintings “, J. Opt. Soc. Am. A. (2008), 25(3): p. 623-630. [10] BAILÃO, A. “Avaliação colorimétrica da alteração de cor de alguns guaches e aguarelas utilizadas na reintegração cromática de bens culturais”, Universidade Católica Editora – Porto, Matrizes da Investigação em Conservação e Restauro I (2014): pp. 13-41. [11] LUO, M. R., CUI, G., RIGG, B.” The development of the CIE 2000 colourdifference formula: CIEDE2000”. Color Res. Appl. (2001) 26: pp. 340–350. doi:10.1002/ col.1049. Book Chapter: [6] AA.VV. - Herramientas integradas de análisis espectrales y colourimétricos aplicadas a la restauración de pintura. In Conservación de Arte Contemporáneo, 14ª Jornada. Spain: Museo Nacional Centro de Arte Reina Sofia, 2013, pp. 33-42. [9] CIE, Colourimetry, in CIE. 2005. pp. 1-82. [12] Linhares, J. M. M., Pinto, P. D., & Nascimento, S. M. C. (2008). The number of discernible colors in natural scenes. Journal of the Optical Society of America A, 25(12), 2918. [13] Aldaba, M. A. et al. “Visual sensitivity to colour errors in images of natural scenes”. Vis Neurosci 23, 2006, pp. 555–559. Website: [5] WiNSOR & NEWTON, Water colour markers. Available at: http://www. winsornewton.com/uk/shop/water-colour/ water-colour-markers [10-07-2016]. [6] AMERICAN SOCIETY FOR TESTING MATERIAL – ASTM – Methods for lightfastness of colourants used in artists Materials (D4303) Specification for artists Watercolour paints (D5067). In http://www. astm.org/Standards/D4303.htm (2016/ 07/ 20)

Nome artigo 97

Abstract Prior to the exhibition Alojz Gangl. A Sculptor on his Way to Modernism (2010) National Gallery of Slovenia had to restore a large number of his sculptures. This paper presents three case studies and focuses on the treatment of losses to decorated surfaces. Each described sculpture is made of a different material: unfired clay, plasticine and plaster. The purpose of this article is to present the conservation treatments of different materials, which share the same approach to aesthetic presentation. When we considered damages aesthetically unacceptable, the chosen approach to fillings and colour reintegration for all three sculptures was the same: to fill and retouch. In two cases, the procedures of filling and colour reintegration were done literally in a single step. We would like to share the conservation treatments of some materials such as unfired clay and plasticine which are rarely documented and we would also like to present a few decisions that are in a certain way different from the past practice FILLING AND COLOUR REINTEGRATION IN A SINGLE STEP Martina Vuga National Gallery of Slovenia; Puharjeva 9, Ljubljana, Slovenia; [email protected]

1. INTRODUCTION National Gallery of Slovenia opened an exhibition of works by the sculptor Alojz Gangl (1859 – 1935) in 2010. He was the beginner of the revival of sculpture in the Slovene lands and the doyen to the first generation of Slovene earlymodern sculptors. (Fig. 1) In the history of Slovene sculpture, he is known above all as the author of the first Slovene public monument, which was erected, to poet and with similar materials. Restorationconservation procedures, methods and materials varied according to the diversity of the constituent materials of the sculptures. It was not possible in the three discussed cases to fulfil every requirement for the reversibility of the materials and treatments. The principle of retreatability (keeping open the options for future treatments) seemed more realistic in this situation. [1] Keywords Filling; Colour re-integration; Sculpture; Unfired clay; Plasticine; Plaster cast. national awakener Valentin Vodnik. [2] Prior to being presented in the exhibition, a number of selected sculptures from different collections and owners needed to be restored. When they were brought to the conservation-restoration workshop in the National Gallery of Slovenia, certain artworks were in a very poor state of preservation because of the fragility of the material itself and frequent or inappropriate handling and/or storing in the past. The poor state of conservation made handling and exhibiting impossible. Sculptures from Gangl’s oeuvre vary in material, from traditional sculpture materials as plaster, wood, terra cotta, bronze and stone to more unusual, provisional and unstable materials like unfired clay, plasticine and other mixed materials. 2. MATERIALS AND METHODS After initial examination the condition of the sculptures was discussed, and goals for the treatment were established. Conservation treatment should return them to visual and physical state as close to “original” as possible and suitable for exhibiting. That meant that dirt needed to be cleaned from the surfaces; losses would be compensated; and finally areas of restoration would be visually integrated with the original surfaces. Because of the materials not so common in the restoration practice, we had to choose the materials and methods on a case-by-case basis. The paper describes three selected case studies. The first discussed sculpture is made of unfired clay, the next one is a plaster cast and the third Figure 1 • Alojz Gangl | (© Bela Krajina Museum)

100 Martina Vuga one is made of plasticine. All three cases share a certain decision: filling and colour re-integration (almost) in a single step. 2.1 Conservation-restoration treatment of St. Agnes, unfired clay The first case study describes the treatment of the sculpture of St. Agnes (38.5 x 14 x 11.5 cm), c 1924, from the Bela Krajina Museum (inv. no. U66). It is made of unfired clay and coated with oil colours. The paint layer imitates the surface of glazed terra cotta. 2.1.1 Condition before treatment Examination of the sculpture before the treatment revealed that clay core had suffered from multiple mechanical injuries. Parts of it have been broken and lost, e.g. the tip of the palm branch the Saint is holding in her right hand (Fig. 2) and some pieces at the back of the figure. 2.1.2 Survey of the described interventions The rarity of sculptures in clay results from the nature of this material. Clay is a material susceptible to humidity, and that is why most of the sculptures made of clay are fired. Restorations performed on similar objects are rarely documented and a survey shows a very wide range of materials used. Some similar cases with the focus on binders and consolidants are listed in the following paragraphs. The first example is the intervention of the 1990s on a clay Sarasvati statue from the Todai-ji Buddhist temple in Nara, Japan. Traditional Japanese glue made of seaweed or its mixture with synthetic resin was used for consolidation of clay and paint layers. Moulded missing parts were adhered with clay soil mixed with addition of different aggregates. [3] The Paraloid B72 was used for the consolidation and bonding in the intervention on a Nodding Figure in 1996. [4] The Aquazol 500 was introduced in the intervention on a Chinese Figure in 2001, where it served in various stages of the treatment, also as a consolidant and filling medium. [5] Ethyl silicate was used for the consolidation and epoxide resin glue for the bonding a sculpture by Mastroinanni in 2005. [6] From described cases, we can conclude there is no generally accepted protocol to selecting materials for interventions on sculptures made of unfired clay. 2.1.3 Materials and methods The conservation treatment of St. Agnes encompassed local consolidation of the clay, cleaning of the painted surface, filling of the cracks and remodelling of the missing parts. A damp cotton swab was used to eliminate the soiling from the painted surface. Remodelling of the missing elements of the sculpture was possible because of the existence of a plaster cast and a bronze version of the same statue. Before remodelling we used Paraloid B72 to consolidate the clay and to make a barrier coat. In selecting materials for the loss compensation and the filling, the specific, water sensitive nature of clay Figure 2 • Alojz Gangl, St. Agnes, unfired clay, before treatment; (© National Gallery of Slovenia, photo: M. Vuga). Figure 3 • Alojz Gangl, St. Agnes, unfired clay, after treatment (© National Gallery of Slovenia, photo: M. Vuga).