Color pigments are colored or fluorescent particulate organic or inorganic solids which usually are insoluble in, and essentially physically and chemically unaffected by, the vehicle or substrate in which they are incorporated. They alter appearance by selective absorption and/or by scattering of light. Pigments are usually dispersed in vehicles or substrates for application, as for instance in the manufacture or inks, paints, plastics or other polymeric materials. Pigments retain a crystal or particulate structure throughout the coloration process.
Due to the large number of pigments available, a classification system is necessary: the Colour Index (C.I.) categorizes each commercially available product, which is given a generic name, a sequential number and a constitution number that summarizes its chemical class, e.g., C.I. Pigment Blue 15, constitution number 74160, used in four color printing.
Color pigments may be organic (i.e., contain carbon) or inorganic. Organic pigments are based on carbon chains and rings. Examples of organic color pigments include: monoazo, diarylide, phthalocyanine, quinacridone, perylene, and anthraquinone pigments. Inorganic pigments, chemical compounds not based on carbon, are usually metallic salts precipitated from solutions or metal oxides. Examples of inorganic color pigments include: bismuth vanadate, complex inorganic color pigments consisting of metal oxides, and iron oxide pigments.
Each pigment is made unique to fit its intended use in commerce. Some important characteristics and customer requirements for choosing the right pigment include: broad shade functionality, durability, opacity, dispersibility, heat stability, solvent resistance, etc.