There is a need for a method to characterize dried oil media dependent upon type, age and origin. Drying oils are composed of mixtures of triglycerides. These are esters formed by the combination of one molecule of the trihydric alcohol glycerol with three molecules selected from a variety of possible fatty acids. The drying-oil triglicerides contain a large proportion of the unsaturated oleic, linoleic and linolenic acids. The double bonds of the unsaturated acids allow them to combine with the oxygen of the air and with one another to form a polymeric network. After saponification the free acids can be isolated. These contain unchanged saturated acids, a little oleic acid and the acids resulting from the decomposition of polyunsaturated acids. These components after conversion into their methyl esters can be esaily separated and quantatively determined by gas chromatography. The drying process depends on the nature of the pigment and the conditions. A tentative relation can be established between the composition of fatty acids (in particular between saturated acids and the products of decomposition) and age. However, the relationship between the quantities of two saturated acids, palmitic and stearic, for the sample given remains essentially unchanged by drying and is in dependent of the pigments present. This differs for the principal drying oils -- linseed, walnut, and poppy -- and seems to be a means for their identification in paint samples. Fatty acids of dried egg are qualitatively similar to those of dried oils but can be distinguished by the very small proportion of bicar boxylic acid produced by the separation, such as azelaric acid. -- AATA