Identification of organic pigments by solution spectrophotometry

Organic pigments can be extracted readily into organic solvents from paints, plastics, inks, and other colored samples. If visible (in some cases near‐infrared) wave‐length spectrophotometric data are obtained from the resulting solutions using a log‐absorbance presentation, the pigments can be identified by matching curve shapes to those in a library of reference curves. Pigment identification is recognized as an important aid in industrial color matching. This article describes research leading to analytical schemes for the solution spectrophotometry of organic pigments, and to the development of an available library of reference curves. The advantages of the logabsorbance presentation are illustrated. A curve‐shape index is described for searching the reference library. The solution‐spectrophotometry method is compared with common alternatives; it is simple and rapid, usable on a micro scale, relatively free from interferences by other constituents of the samples, capable of identifying impure samples and the components of mixtures, and applicable with readily available equipment.