The removability of naturally aged synthetic picture varnishes has been examined on more than 50 paintings. Most of these paintings had been coated with either poly(isoamyl methacrylate) or poly(n-butyl methacrylate). Since these aged methacrylate coatings were applied between 10 and 40 years ago, questions had been posed about possible cross-linking of the polymer chains, which would make them more difficult to remove with solvents or even render them completely insoluble. These questions were investigated by applying solvents of increasing polarity to the varnish by swab, and analyzing the material removed by infrared spectroscopy. All coatings were found to be removable with solvents, although often fairly polar solvent mixtures were necessary.Only 5 of 25 paintings suspected of being coated with poly(isoamyl methacrylate) were found to be coated with this varnish. The varnish, a type known as 27H, was removed with relatively mild solvents, often by swelling. Thirty-one paintings coated with poly(n-butyl methacrylate) were examined. Although solvents more polar than acetone were not required for removal of the coatings, concerns were raised about the sensitivity of the paint films of early American paintings to that solvent. In addition, although these coatings are removable today, the future aging behavior of these varnishes under the conditions of exposure at the National Gallery of Art, where ultraviolet filters are in place, has not been determined. Continued systematic monitoring of the aging behavior of these varnishes on selected paintings will be carried out.
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