New Insights into the Cleaning of Paintings

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122 • smithsonian contributions to museum conservation Table 1. Results of the first sets of 64 cleaning tests on Chemistry as evaluated by visual inspection, by microcopic examination (magnification 63×), and under UV irradiation. For the evaluation numbers, a negative value indicates pigment loss: −6, uneven minimal cleaning; −5, even minimal cleaning; −4, uneven average cleaning; −3, even average cleaning; −2, uneven good cleaning; −1, even good cleaning. A positive value indicates no pigment loss: 1, uneven minimal cleaning; 2, even minimal cleaning; 3, uneven average cleaning; 4, even average cleaning; 5, uneven good cleaning; 6, even good cleaning. Color Test details Dark blue, diluted Blue mixed with white Dark green, diluted Green mixed with white Dark red, diluted Red mixed with white Semisolid paint on underdrawing Bare ground Application area laboratory flask below boy laboratory flask below girl background behind girl background behind boy test tube cloud behind boy girl’s ankle omnipresent Pigments ultramarine, Prussian blue, cobalt blue cobalt blue, emerald green plus white emerald green, chrome green emerald green, chrome green plus white vermilion vermilion plus white vermilion plus white on carbon black zinc white, lead white, chalk Test 1, natural saliva 2 6 2 5 −4 3 1 1 Test 2, Marlipal 1618/25 −5 6 6 5 −3 6 4 3 Test 3, Brij 700 gel −1 6 6 3 −1 3 −1 3 Test 4, Triton X- 100 gel −1 6 6 6 −1 6 −1 6 Test 5, triammonium citrate (cotton swab) −5 6 6 6 −3 3 −1 6 Test 6, triammonium citrate (sponge) −5 3 4 3 –3 6 1 1 Test 7, vulcanized natural gum sponge 2 2 2 2 2 2 2 2 Test 8, bread dough 2 2 6 3 4 2 2 3 first two were identified on the exposed areas and are responsible for the gray dust layer. The latter two are still invisible to the naked eye. The metal soaps were identified on both exposed and unexposed areas, but the zinc oxalates were only identified on the exposed surface and not below the frame. When metal soaps become visible, they are seen as white surface deposits, and they are generally regarded as rather common in oil paintings from the 1600s to the early 1900s (van Loon, 2008). They form through the saponification of unsaturated fatty acids in either the binding medium and/or the ground layers. Their development is promoted by various factors, including high temperature and relative humidity (van Loon, 2008). They are removable by mechanical means or can be disguised by increasing their saturation with varnish. Saturation is, however, no option for the Munch Aula paintings since any kind of surface saturation will reveal the darkened canvas in all the areas of bare ground. When visible, copper and calcium oxalates have been reported as either grayish brown surface crusts on easel paintings (Higgit and White, 2005) or as semiopaque film on murals (Nevin et al., 2008). They are highly insoluble and thus very difficult to remove by traditional methods. There is no known literature on the appearances of zinc oxalate salts or on their removal. If, or when, the zinc salts become visible on the Aula paintings (or any other paintings by Munch), they might cause radical changes to the appearances of the paintings and the artist’s intent. Further research must be employed to delay the growth of possible visible and untreatable intrusions of the zinc oxalates on the paintings in question.
number 3 • 123 Acknowledgment Access to the MOLAB was obtained thanks to the 6th Framework Programme (contract Eu- ARTECH, RII3- CT- 2004- 506171). REFERENCES Frøysaker, T., C. Miliani, and M. Liu. 2011. Non- invasive Evaluation of Cleaning Tests Performed on Chemistry (1909–1916). A Large and Unvarnished Oil Painting on Canvas by Edvard Munch. Restauro, 4:53–63. Higgit C., and R. White. 2005. Analyses of Paint Media: New Studies on Italian Paintings of the Fifteenth and Sixteenth Centuries. National Gallery Technical Bulletin, 26:88–104. Nevin, A., J. L. Melia, I. Osticioli, G. Gautier, and M. P. Colombini. 2008. The Identification of Copper Oxalates in a 16th Century Cypriot Exterior Wall Painting Using Micro FTIR, Micro Raman Spectroscopy and Gas Chromatography- Mass Spectrometry. Journal of Cultural Heritage, 9(2):154–161. http://dx .doi.org/10.1016/j.culher.2007.10.002. van Loon, A. 2008. Color Changes and Chemical Reactivity in Seventeenth- Century Oil Paintings. MOLART Reports 14. Amsterdam: Netherlands Organization for Scientific Research. FIGURE 3. Noninvasive reflectance mid- infrared FTIR measurements: comparison of a spectrum collected on an uncleaned area (II, black line) with a spectrum of an area below the frame (I, gray line). The spectral region used for the identification of the different compounds is labeled: asterisk (*), diagnostic bands for Zn oxalates; section sign (§), diagnostic bands for Zn and Pb soaps, i.e., carboxylates; and dollar sign ($), diagnostic bands for silicates and sulfates. The transmittance of hydrated zinc oxalate is also shown (III, red line).
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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 and 148: Extended Abstract—A Preliminary S
Page 149: number 3 • 137 Acknowledgments An
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
Page 169: number 3 • 157 alien und Methoden
Page 181 and 182: Extended Abstract—The Removal of
Page 183 and 184: number 3 • 171 RESULTS AND DISCUS
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number 3 • 173 FIGURE 3. The SEM
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Extended Abstract—Cleaning Issues
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number 3 • 177 Acknowledgments Th
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180 • smithsonian contributions t
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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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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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