Twenty-two pigments commonly used in artists' paints were investigated by recording the fourth-derivative (d 4) ultraviolet-visible spectra. Dimethyl sulphoxide was used as a universal solvent. It was possible to distinguish pigments which were chemically very similar and of the same colour, and to quantify the components of binary mixtures without separation by using side-peak-side ratio computations. Acrylic or oil media had no influence on the derivative spectra. For mixtures of more than two components, the pigments were separated by thin-layer chromatography and the d 4-spectra were recorded directly from the developed spots; 10 ng of each pigment in 5 μl of solvent was enough for the analysis.