New Insights into the Cleaning of Paintings
SCMC-0003 SCMC-0003
58 • smithsonian contributions to museum conservation REFERENCES Erhardt, D., R. Cunningham, and S. Rasanen. 2001. “Extraction of Material from Oil Paints by Solvents.” In Materials Issues in Art and Archaeology VI, ed. P. B. Vandiver, M. Goodway, J. R. Druzik, and J. L. Mass, pp. 43–52. Boston: Materials Research Society. Erhardt, D., C. S. Tumosa, and M. F. Mecklenburg. 2000. Can Artists’ Oil Paints Be Accelerated Aged? Polymer Preprints 41(2):1790–1791. Mills, J. S., and R. White. 1987. The Organic Chemistry of Museum Objects. London: Butterworths. Tumosa, C. S., D. Erhardt, M. F. Mecklenburg, and X. Su. 2005. “Linseed Oil Paint as Ionomer: Synthesis and Characterization.” In Materials Issues in Art and Archaeology VII, ed. P. B. Vandiver, J. L. Mass, and A. Murray, pp. 25–31. Materials Research Society Symposia Proceedings 852. Boston: Materials Research Society. Tumosa, C. S., J. Millard, D. Erhardt, and M. F. Mecklenburg. 1999. “Effects of Solvents on the Physical Properties of Paint Films.” In Preprints 12th Triennial Meeting ICOM Lisbon, ed. J. Bridgland, pp. 347–352. London: James & James. van den Berg, J. D. J. 2002. Analytical Chemical Studies on Traditional Linseed Oil Paints. pp. 9–52. Amsterdam: Molart (FOM).
The Influence of Pigments and Ion Migration on the Durability of Drying Oil and Alkyd Paints Marion F. Mecklenburg, Charles S. Tumosa, and Edward P. Vicenzi Abstract. The durability of paints made with drying oil and alkyd mediums refers to their resistance to atmospheric moisture and solvents used in the cleaning of paintings. Ideally, after a reasonable drying period, these paints develop sufficient polymerization and cross-linking to resist swelling and deterioration from most cleaning solvents. Although there has been considerable research on the effects of certain metal ions on the autoxidation of drying oils, that research cannot be used to determine the long-term stability of paints made with drying oils. Current research suggests that a wide variety of metal ions affects the ultimate film formation of oil paints. The exact reaction of those ions with the drying oils is not clearly understood. But there is now considerable evidence that those metal ions are not only capable of migrating throughout a given paint layer but also sufficiently mobile to migrate from one paint layer to an adjacent one in a painting. In this case the migrating ions are capable of either enhancing or degrading the adjacent paint layers. Because artists’ alkyd paints contain considerable levels of drying oils, they can react with pigments in an manner analogous to oil paints and therefore will be part of this discussion. INTRODUCTION Marion F. Mecklenburg and Edward P. Vicenzi, Museum Conservation Institute, Smithsonian Institution, Museum Support Center, 4210 Silver Hill Road, Suitland, Maryland 20746, USA. Charles S. Tumosa, Department of Criminology, Criminal Justice and Forensic Studies, University of Baltimore, 1420 North Charles Street, Baltimore, Maryland 21201, USA. Correspondence: Marion F. Mecklenburg, mecklenburgm@ si.edu; Charles S. Tumosa, cstchemist@aol.com; Edward P. Vicenzi, vicenzie@si.edu. Manuscript received 19 November 2010; accepted 24 August 2012. To a practicing painting conservator it can be puzzling that oil paints made with specific pigments, such as organic reds and blacks and some of the earth colors, are easily and safely cleaned on some paintings whereas they are quite sensitive to solvents on others. The question regarding the resistance to damage from cleaning solvents comes down to what enhanced the durability of these paints. There has been considerable research on the effects of certain metal ions on the autoxidation of drying oils. For example, it has been shown that metal ions such as Co 2+ , Mn 2+ , and Fe 2+ are considered “primary” driers and act during oxidation, whereas Pb 2+ , Zr 4+ , and Al 3+ are “secondary” driers and are active during polymerization. Finally, Ca 2+ , K + , and Zn 2+ are considered auxiliary driers as they act to modify the activity of the primary driers (van den Berg, 2002; Tumosa and Mecklenburg, 2005). More importantly, it is generally agreed that the ability of a metal compound to catalyze the oxidation of the oil and form a film depends upon both the solubility and the dissociation of the metal ion in the oil (Olson, 1921; Marling, 1927; Bennett, 1941; Morgan, 1951; Stewart, 1967). In order to get sufficient concentrations of metal ions to catalyze the oxidation of the oil, either the metal ions must be added separately (dissolved or reacted) or the metal ions must dissolve from the pigment itself. Dissociation into metal ions is quite important, and a compound such as tetraethyl lead, which has covalent bonding and does not dissociate, exerts no influence on the drying of oil (Bennett, 1941). The requirement for a metal ion
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58 • smithsonian contributions to museum conservation<br />
REFERENCES<br />
Erhardt, D., R. Cunningham, and S. Rasanen. 2001. “Extraction <strong>of</strong> Material from<br />
Oil Paints by Solvents.” In Materials Issues in Art and Archaeology VI, ed.<br />
P. B. Vandiver, M. Goodway, J. R. Druzik, and J. L. Mass, pp. 43–52. Boston:<br />
Materials Research Society.<br />
Erhardt, D., C. S. Tumosa, and M. F. Mecklenburg. 2000. Can Artists’ Oil Paints Be<br />
Accelerated Aged? Polymer Preprints 41(2):1790–1791.<br />
Mills, J. S., and R. White. 1987. The Organic Chemistry <strong>of</strong> Museum Objects. London:<br />
Butterworths.<br />
Tumosa, C. S., D. Erhardt, M. F. Mecklenburg, and X. Su. 2005. “Linseed Oil Paint<br />
as Ionomer: Syn<strong>the</strong>sis and Characterization.” In Materials Issues in Art and<br />
Archaeology VII, ed. P. B. Vandiver, J. L. Mass, and A. Murray, pp. 25–31.<br />
Materials Research Society Symposia Proceedings 852. Boston: Materials<br />
Research Society.<br />
Tumosa, C. S., J. Millard, D. Erhardt, and M. F. Mecklenburg. 1999. “Effects <strong>of</strong><br />
Solvents on <strong>the</strong> Physical Properties <strong>of</strong> Paint Films.” In Preprints 12th Triennial<br />
Meeting ICOM Lisbon, ed. J. Bridgland, pp. 347–352. London: James<br />
& James.<br />
van den Berg, J. D. J. 2002. Analytical Chemical Studies on Traditional Linseed Oil<br />
Paints. pp. 9–52. Amsterdam: Molart (FOM).
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