Pigments generally are insoluble and are applied not as solutions but as finely ground solid particles mixed with a liquid. In general, the same pigments are employed in oil- and water-based paints, printing inks, and plastics. Pigments may be organic (i.e., contain carbon) or inorganic.
For the most part, organic pigments are presently synthesized from aromatic hydrocarbons. These are compounds containing structures of carbon atoms with hydrogen atoms attached that are formed in closed rings. Organic pigments include azo pigments, which contain a nitrogen group; they account for most of the organic red, orange, and yellow pigments. Copper phthalocyanines provide brilliant, strong blues and greens that are unusually colourfast for organic colours. Some pigments, such as fluorescent ones, are simply dyes that have been rendered insoluble by chemical reaction.