The ageing of egg yolk, one of the proteinaceous media used by artists, was studied. Films of egg yolk alone, or egg mixed with linseed oil or gum arabic, with and without the addition of pigments (cobalt aluminate, ferric oxide, barium sulphate) were prepared. These were aged in the dark at 40 degrees C. Films were also prepared and aged in light, of binding media alone and also with the addition of a drier, cobalt octonate. Ageing was followed from the amount of material extractable in water, and in trichloromethane-methanol mixtures. Changes in double-bond content of the egg yolk and egg yolk-linseed oil mixtures were determined using the iodine number method. Disc electrophoresis was used to check changes in the protein fraction after extraction of the lipids. The egg yolk films were studied using infrared analysis. The results obtained indicated that these films resisted oxidative cross-linking. Tables, graphs, references.