Possible uses for thin-layer chromatography in the investigation of organic pigments are examined. The tests are extended to include sparingly soluble azo and polycyclic pigments. The results for the various classes of pigments are shown in the form of R values. A method of identifying chemically identical pigments which differ in physical prop-erties such as particle size or crystal structure is described. The principle of this method consists in visualising differences in solubility by chro-matographic means. -- AATA