Soap was found to have formed on the surface of some oil paintings
The National Gallery in London has been carrying out a detailed study of tiny white inclusions in the surface of many of its paintings (dating from 13th to late 18th century). Using IR microscopy, scanning electron microscopy, energy-dispersive x-ray analysis and other techniques, researchers at the gallery have shown that these inclusions consist of lead soaps (especially lead azelate), which are the result of metal-based pigments reacting with the oil used to make paint. It is hoped that the results of these studies will influence decisions on the future storage, conservation and exhibition of valuable paintings.
Chemistry World (April 2004)
Ed. Formation of lead (and zinc) soaps on the surface of paintings has continued to be studied around the world, for example at the Metropolitan Museum of Art in New York, US, and at the UK’s National Gallery in 2013. For a recent article on soap formation on oil paintings, see J Catalano et al, Appl. Spectrosc., 2014, 68, 280 (DOI: 10.1366/13-07209).