New Insights into the Cleaning of Paintings

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136 • smithsonian contributions to museum conservation In order to ensure reproducibility and accuracy in the cleaning operation, mock- ups were immersed in the cleaning solution and tests were run in duplicate. As previous reports show that most of the material lixiviated from a paint sample occurs in the first few minutes (Ormsby and Learner, 2009), the effect of a fiveminute immersion was evaluated. The effects of cleaning (both efficacy of dirt removal and changes to the paint film) were assessed by the following: level of dirt removal, color change, loss of extractable material, detection of residues, and disruption to the paint surface. Changes to the paint surface morphology were monitored by atomic force microscopy (AFM) in vibrating mode on areas of 50 × 50, 10 × 10 and 2 × 2 mm 2 . Alterations in the surfaces’ chemical composition were assessed by Fourier transform infrared spectroscopy attenuated total reflectance (ATR), and color coordinates were collected with a portable colorimeter, using the CIE L*a*b* system. Roughness values R a obtained with AFM were calculated on the 10 × 10 mm 2 scan areas, as an average of five selected 2 × 2 mm 2 areas. The value presented is the average of the two replicates. RESULTS AND DISCUSSION Artificial aging studies indicate that loss of paint plasticizer, diisobutyl phthalate (DiBP), is the major alteration between aged and unaged samples (Ferreira et al., 2010). The ATR spectra from the artificially aged control sample showed no significant signs of a surface enrichment with DiBP. Therefore, it was expected that immersion could only remove negligible quantities of plasticizer still present on the tests films. As expected, only minor changes were seen in ATR spectra that can be tentatively correlated to the extraction of this additive (Figure 1). Moreover, DiBP was not detected among the residues remaining after immersion. Because of the irregular surface topography and affinity for dirt that is retained by the paint surface, immersion of the samples was not efficient for dirt removal. This was confirmed both by optical microscopy and colorimetry. Smaller AFM scan areas were found to be the most useful because of the heterogeneous nature of the paint surface and the technical difficulties encountered when scanning large features deposited on the samples. Moreover, with the 10 × 10 and 2 × 2 mm 2 areas changes in the latex surface can be seen with high detail (Figure 2). Pure water did not induce relevant alterations on the morphology of the white paint. However, with the aqueous solution of Brij700S the smoothness of the latex particles is lost, and the polymer surface displays a more irregular texture, which could be the result of surfactant residues left on the paint. Large and protruding features appeared on the paint’s surface after white spirit immersion. Cleaning with an eraser resulted in both particles and/or eraser additives being left on the surface. These residues could not be identified with ATR, probably because of their small FIGURE 1. The ATR infrared spectra. (top) Artificial aging of the sample induces loss of the plasticizer, as seen from comparison of the circled peaks. (bottom) The aged control sample shows no plasticizer enrichment on the surface, and therefore only minor differences can be observed in those peaks after water immersion. quantity, but they are clearly related to the eraser because the pattern left in the polymer surface is similar to that observed when using it directly on mica sheets. Moreover, the physical abrasion provoked by the mechanical action can account for the decrease in the surface roughness. CONCLUSIONS These preliminary results offer a first insight into the response of PVAc emulsion paints to cleaning procedures. Surface roughness was not significantly affected with the immersion of the samples in any of the tested solvents. However, changes in surface morphology were observed for the surfactant solution and even more for the white spirit. Immersion of the samples was insufficient to obtain dirt removal. Moreover, surfactant residues were not effectively removed. The most significant changes were introduced by the eraser. Concern should be raised about using Akapad for dirt removal in Sarmento’s White Paintings as these paints might be liable to mechanical damage. Physical disruption of the latex paint was only detected at the nanoscale; however, it could result in a flattening of the paint surface that is contrary to the distinctive pigment agglomerates and filler texture typical of these paintings. Work is currently under way to study and test samples prepared by the artist and naturally aged (20 years) as well as on model samples reproducing the artist’s technique.
number 3 • 137 Acknowledgments Ana Pereira acknowledges Fundação para a Ciência e Tecnologia (FCT/MCTES) for her Ph.D. grant (SFRH/BD/39917/2007) and Joana Lia for kindly providing the paint samples. This work has also been supported by Fundação para a Ciência e a Tecnologia through grant no. PEst-C/EQB/LA0006/2011. REFERENCES Ferreira, J. L., M. J. Melo, and A. M. Ramos. 2010. Poly(vinyl acetate) Paints in Works of Art: A Photochemical Approach. Part 1. Polymer Degradation and Stability, 95:453–461. http://dx.doi.org/10.1016/j.polymdegradstab.2010.01.015. Ormsby, B., and T. Learner. 2009. The Effects of Wet Surface Cleaning Treatments on Acrylic Emulsion Artist’s Paints—A Review of Recent Scientific Research. Reviews in Conservation, 10:29–41. Pereira, A. I., S. Schäfer, and M. J. Melo. 2007. “Julião Sarmento, a Portuguese Artist at Work: Study of Just a Skin Affair from 1988.” In Modern Paints Uncovered: Proceedings from the Modern Paints Uncovered Symposium, ed. T. J. S. Learner, P. Smythen, J. W. Krueger, and M. R. Schilling, pp. 294–295. Los Angeles: The Getty Conservation Institute. FIGURE 2. The AFM amplitude images of artificially aged PVAc white paints. For the aged control and solvent- immersed samples, images of surface areas are presented (10 × 10 mm 2 at the left and 2 × 2 mm 2 at the right); area sizes for the erased samples are indicated below the images. Average roughness R a is listed below each sample.
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Smithsonian Institution Scholarly P
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smithsonian contributions to museum
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Contents PREFACE ACKNOWLEDGMENTS
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number 3 • v Extended Abstract—
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viii • smithsonian contributions
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The Removal of Patina Stephen Gritt
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number 3 • 3 and conceals its bea
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number 3 • 5 REFERENCES Algarotti
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8 • smithsonian contributions to
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Surface Cleaning of Paintings and P
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number 3 • 19 methods for cleanin
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number 3 • 21 not the varnish its
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Extended Abstract—A Preliminary I
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number 3 • 25 FIGURE 3. Detail of
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Extended Abstract—A New Documenta
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number 3 • 33 FIGURE 2. Recording
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Oil Paints: The Chemistry of Drying
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number 3 • 53 FIGURE 3. Weight ch
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number 3 • 55 FIGURE 7. Formation
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number 3 • 57 FIGURE 11. Differen
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The Influence of Pigments and Ion M
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number 3 • 61 FIGURE 3. Mechanica
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number 3 • 63 FIGURE 7. Mechanica
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number 3 • 65 observation that co
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number 3 • 67 • Not all pigment
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Page 101 and 102: Characterization and Stability Issu
Page 103 and 104: number 3 • 91 FIGURE 2. Film form
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Page 107: number 3 • 95 allows identificati
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Page 119 and 120: Sensitivity of Oil Paint Surfaces t
Page 121 and 122: number 3 • 109 Analytical Methods
Page 123 and 124: number 3 • 111 The method for ass
Page 125 and 126: number 3 • 113 FIGURE 6. Secondar
Page 127 and 128: Extended Abstract—The Effect of C
Page 129: number 3 • 117 Table 1. Surface m
Page 137 and 138: Multitechnique Approach to Evaluate
Page 139 and 140: number 3 • 127 RESULTS AND DISCUS
Page 141 and 142: number 3 • 129 FIGURE 4. The SEM
Page 143 and 144: number 3 • 131 FIGURE 7. (top) St
Page 145 and 146: number 3 • 133 FIGURE 10. Stress-
Page 147: Extended Abstract—A Preliminary S
Page 159 and 160: Cleaning of Acrylic Emulsion Paints
Page 161 and 162: number 3 • 149 advocates of publi
Page 163 and 164: number 3 • 151 2.5, 3.5, 4.5, 5.5
Page 165 and 166: number 3 • 153 ethoxylate units i
Page 167 and 168: number 3 • 155 FIGURE 5. Golden A
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Page 181 and 182: Extended Abstract—The Removal of
Page 183 and 184: number 3 • 171 RESULTS AND DISCUS
Page 185 and 186: number 3 • 173 FIGURE 3. The SEM
Page 187 and 188: Extended Abstract—Cleaning Issues
Page 189: number 3 • 177 Acknowledgments Th
Page 197 and 198: Effects of Commercial Soaps on Unva
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number 3 • 187 The aqueous and or
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number 3 • 189 all tests. The res
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number 3 • 191 palmitic and stear
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FIGURE 5. Scanning electron microsc
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number 3 • 195 FIGURE 6. Confocal
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Extended Abstract—Tissue Gel Comp
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number 3 • 199 • The capillary
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202 • smithsonian contributions t
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Extended Abstract—Use of Agar Cyc
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number 3 • 207 FIGURE 4. The FTIR
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Extended Abstract—The Schlürfer:
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number 3 • 223 FIGURE 3. Removal
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Extended Abstract—Surface Cleanin
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number 3 • 227 Table 3. Cleaning
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Extended Abstract—Laser Cleaning
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Ending Note: Summary of Panel Discu
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Index TABLES in BOLD; Figures in It
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number 3 • 243 polyvinyl acetate
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