AIC's 41st Annual Meeting

Water-borne emulsion polymer paints have enabled artists to move aesthetically far from traditional limitations of oil paints, but have left us with a cultural legacy replete with some of the greatest challenges in terms of conserving and exhibiting these treasures. Methods for treating and exhibiting traditional oil paintings have been developed over the last five centuries and their suggested display and storage parameters have principally influenced the design of the modern museum environment. The exact parameters for acrylic paintings, particularly those of cleaning methodology, are not as well understood. To better define acrylic cleaning considerations, we have examined pH, conductivity, and specific ion effects of potential aqueous cleaning solutions on a series of commercial acrylic paints in order to minimize the extraction of paint film components and minimize physical distortion of the paint film. 3-D microscopic techniques were developed to characterize the physical changes (volume and surface roughness) and liquid chromatography-tandem mass spectrometry was used to characterize the extent of extracted surface surfactant (Triton X-305) following paint film exposure to the cleaning solution. The tested paint films in this study exhibited an isotonic point below which swelling and extraction is significant, and above which the swelling and extraction is diminished. Experimentally, optimization of conductivity and the ionic species in solution reduced both the physical film changes and surfactant extraction from acrylic paint films; in contrast, pH appears to be of limited use in controlling aqueous cleaning effects. Additionally, there seems to be a specific ion effect for both swelling and de-swelling in acrylic paint films that can be rationalized through the Hofmeister Series.

Recent work funded through the National Science Foundation has focused on the formulation of microemulsions incorporating the optimized aqueous cleaning solution conditions to minimize aqueous solution contact with the paint film surface that included conservator-testing of optimized microemulsion cleaning solutions at the Cleaning Acrylic Painting Surfaces (CAPS 2012) workshop. 2D-desorption electrospray mass spectrometry (2D DESI-MS) is being explored for the first time for the chemical analysis and chemical imaging of art surfaces. DESI-MS and enhanced modes of the linear ion trap mass analyzer can chemically map surfactant on the paint surface before and after microemulsion cleaning and surfactant oxidation products during aging studies. 2D DESI is being investigated as a complementary technique to electron spin resonance (ESR) imaging to image free radicals and ESR silent photoproducts. Studies that investigate the environmental storage conditions (relative humidity, temperature, vibration) on the migration of surfactant to the paint film surface will also be discussed. The introduction of 2D DESI offers a new molecular imaging technique to the museum conservation laboratory and will likely find utility in projects outside the scope of the present work. This paper will discuss the findings of this study and suggest new guidelines for the cleaning of acrylic paintings in museums.