Conservar Património, no. 2 , 2005, pp. 3-12, Portuguese

Oils, paintings and chemistry

Maria Eduarda Machado de Araújo
Departamento de Química e Bioquímica
Faculdade de Ciências da Universidade de Lisboa
1749-016 Lisboa, Portugal
eduaraujo@fc.ul.pt

Abstract

In oil paintings artists use oils to apply pigments. These oils firstly are liquid and then solidify in a thin film. Many chemical reactions are involved in drying and also in the aging of these oils. Drying is a continuous process that begins with the oxidation of insaturated fatty acids from triglycerides to originate peroxides. These compounds suffer a cascade of reactions that lead to cross linking bonds between fatty acids residues, transforming the oil in a solid film. Identification of the film oil is possible using the palmitic/stearic ratio (P/S) by chromatographic (GC) and/or spectroscopic techniques. Sterol composition, phytosterols or cholesterol, determined by GC-MS or FTIR techniques, allows investigators to distinguish between oil painting and a temper one that used egg as the binding medium.

Keywords

Oils, paintings, drying, ageing, peroxides.

Language

Portuguese

Original title

Óleos, pintura e química