New Insights into the Cleaning of Paintings

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100 • smithsonian contributions to museum conservation FIGURE 3. Swelling of (A) oil paint and (B) alkyd paint in binary solvent mixtures. All series exhibit nonideal behavior. Cosolvents (Co- S.) are H, n- hexane; T, toluene; C, chloroform; D, diethyl ether; A, acetone; and E, ethanol. with the polymer even though it is virtually incompatible with the cosolvent (Wessling, 1970). These swelling anomalies conspicuously correlate with a change in boiling point (Hellwege, 1975) or the exceed volume V E (Fermeglia and Lapasin, 1988) of binary mixtures. In turn, this correlation can be explained by a change in cohesive properties (Figure 5). These anomalies occur when the intermolecular interaction between the individual components is smaller than that between structurally similar molecules. The formation of associates of the polar solvent component within the mixed system leads to a local reduction in the cohesive energy between liquid clusters of variable nature. Such mixtures can be described as microheterogenic systems (Murdoch et al., 2002). From the perspective of an energy landscape (Abraham et al., 2007), the system represents basins with lower cohesive energy between the solvent phases (Figure 6). Since energy minima are necessary for cavity formation, the distribution of the solute in the surrounding liquid is, in general, preferential in microheterogeneous mixtures. Thus, even very small amounts of ethanol in an arbitrary binary solvent mixture can dramatically increase the swelling action. The opposite applies in the case of an increase in cohesive energy (Sivakumar and Naidu, 1997). This is evident, for example, in the case of acetone- chloroform mixtures, where the interaction between the molecules of the different solvents forming hydrogen bonds is much stronger than between molecules within the individual solvents. No cluster effects can thus be observed. As a result, the nonideal behavior of solvent mixtures is dominated by intermolecular forces within the liquid and therefore is largely independent of the solvation process. Leaching Capacity of Solvent Mixtures The properties of solubilization discussed above and the swelling capacity of solvent mixtures are directly relevant to the
number 3 • 101 FIGURE 4. Swelling anomalies of oil (shaded circles) and alkyd paint films (open circles) in solvent mixtures containing acetone and ethanol. Apart from the chloroform- acetone mixture (shaded gray), all series show positive anomalies. These mixtures thus have a significantly increased swelling capacity exceeding that of the pure solvents several times. FIGURE 5. (top) Nonideal swelling of oil paint in relation to (bottom) the nonideal boiling temperatures of the binary mixtures. Mixtures containing polar solvents show an inverse relationship between boiling point and swelling behavior. Deviation from ideal behavior increases with an increase in polarity difference of the solvents mixed. Gray shading highlights negative anomalies.
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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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Page 63 and 64: Oil Paints: The Chemistry of Drying
Page 65 and 66: number 3 • 53 FIGURE 3. Weight ch
Page 67 and 68: number 3 • 55 FIGURE 7. Formation
Page 69 and 70: number 3 • 57 FIGURE 11. Differen
Page 71 and 72: The Influence of Pigments and Ion M
Page 73 and 74: number 3 • 61 FIGURE 3. Mechanica
Page 75 and 76: number 3 • 63 FIGURE 7. Mechanica
Page 77 and 78: number 3 • 65 observation that co
Page 79: 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
Page 105 and 106: number 3 • 93 (Saunders, 1973). T
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
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number 3 • 151 2.5, 3.5, 4.5, 5.5
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number 3 • 153 ethoxylate units i
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number 3 • 155 FIGURE 5. Golden A
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number 3 • 157 alien und Methoden
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160 • smithsonian contributions t
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Extended Abstract—The Removal of
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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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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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