Colorants are normally understood to include both pigments and dyestu£. Pigments refer mainly to inorganic salts and oxides, such as iron and chromium oxides, which are usually dispersed in crystal or powder form in an application medium. ™e color properties of the dispersion depends on the particle size and form of the pigment. Pigment colorants tend to be highly durable, heat stable, solvent resistant, lightfast, and migration fast. On the other hand, they also tend to be hard to process and have poor color brilliance and strength. Dyes (also called dyestu£) are conventionally understood to refer to organic molecules dissolved, as molecular chromophores, in the application medium. Examples are azo dyes, coumarin dyes, and perylene dyes. ™e color imparted by dyestu£ to the resulting solution depends on the electronic properties of the chromophore molecule. Dyestu£ colorants tend to have excellent brilliance and color strength, and are typically easy to process, but also have poor durability, poor heat and solvent stability, and high migration. Because of the contrasting properties of both types of colorants, much work has been done trying to improve the attributes of each class of colorant.