The chemistry of artists’ oil paints

Oil paintings from the 20th and 21st centuries present a range of conservation issues different from those of paintings realised in the previous centuries. These issues are believed to be correlated with the use of manufactured artists’ oil paints, which contained driers, fillers and stabilisers, modified oils, semi-drying oils and a range of pigments. The chemical nature of the changes occurring in the film former as a consequence of degradation is, in most cases, not fully understood at the molecular level. It has been hypothesised that some degradation phenomena taking place in oil paintings - especially those produced with modern manufactured artists’ oil paints - are related to the chemical nature of the oil cross-linked network, and in particular, to a low degree of polymerization and a high degree of oxidation. The polymeric as well as the highly complex multi-component nature of paint films do not allow a straightforward characterization of its molecular features. However, a useful approach to improve our understanding of the chemical structure of the paint film is the characterisation of the process leading to its formation: the curing. In this context, the principal aim of my Ph.D. project was to implement a methodological approach to monitor physico-chemical changes of oil paints upon curing and ageing. In particular, great effort was made to design a methodological approach able to characterise the effect of different oils, pigments and driers on the autoxidation kinetics, to monitor the evolution of oxidation products, to evaluate the magnitude of oxidative degradation and cross-linking phenomena, and to determine the structure of the cross-linked fractions.