The influence of metal stearates on the water sensitivity of modern oil paints. In Conservation of Modern Oil Paintings

The influence of free metal stearates, other metal soaps and free fatty acids on the water sensitivity of modern oil paint swatches from three brands of artists’ manufactured tube paints was investigated. The swatches produced in 2006 and tested for water sensitivity in 2008 were re-tested, and changes in sensitivity were recorded. Swatches with a range of sensitivity to water and those that exhibited visible surface deterioration were selected for chemical and optical characterisation. This included a novel method of sample preparation for gas chromatography coupled with mass spectrometry (GC/MS) for quantitative analysis of free fatty and dicarboxylic acids and related metal soaps. Results suggested that the proportion of free fatty acids and metal soaps in the swatches does not relate to water sensitivity of the paint surface. It is therefore likely that the polymeric/ionomeric network plays an important role in water sensitivity. Results showed that fatty acid efflorescence is linked with high levels of free fatty acids (FFA) in the paint swatch and that the extent of the efflorescence is proportional to the quantitative results for free fatty acids found in the GC/MS analyses