Comparative study of the effect of traditional pigments on artificially aged oil paint systems using complementary analytical techniques

The changes observed in the bulk physical properties of a series of artificially light-aged pigmented linseed oil paint films have been linked to differences in the chemistry (at a molecular level) of the organic binding medium. Using a combination of spectroscopic, chromatographic and spectrometric techniques it is possible to identify various sub groupings within the pigmented films based on the proportions of free, ester- and metal-bound acids and polymeric network components, and the chemical composition of these fractions. Paint systems with a low degree of hydrolysis (malachite, lead white and Naples yellow under the experimental conditions) are physically hard. In paints with a high degree of hydrolysis (vermilion and vine black), monocarboxylic acids are mainly present in free form resulting in a soft film. In other paint films there is clearer indication of reaction between pigments (lead white, cochineal lake, Naples yellow and smalt) and oil, with metal carboxylate-containing products being identified. Although these artificially aged reconstructions are not directly comparable with naturally aged samples, the study results in information regarding the drying and ageing of oil paint, the influence of pigments on these processes and pigment-medium interactions.
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