Dyes and Pigments

The color of a pigment is deposited when the spreading agent dries or hardens. The physical property of a pigment does not change when it is mixed with the agent. Some organic dyes can be converted into pigments. For example, dyes that have salt groups in their chemical structure can be made into an insoluble salt by replacing the sodium molecule with a calcium molecule. Dyes that depend on chemical treatment to become soluble such as indigo, can also be used as pigments. Pigments are also classified, in addition to classification mentioned above, by their color–white, transparent, or colored.

Pigments are also used for other purposes than just coloring a medium. Anticorrosive pigments, such oxides of lead, are added to paint to prevent the rusting of objects made of iron. Metallic pigments such as aluminum, bronze, and nickel are added to paints and plastics for decorative, glittery effects. Pulverized mica produces a sparkle effect and bismuth oxychloride gives a pearlescent appearance to paints and cosmetics.

Luminous pigments have the ability to radiate visible light when exposed to various energy sources. The luminous pigments that emit light after exposure to a light source and placed in the dark are called phosphorescent or commonly, glow-in-the-dark. Phosphorescent pigments are made from zinc or calcium sulfides and other mineral additives that produce the effect. Another good example of how dyes are made into pigments are some of the fluorescent pigments. Fluorescent pigments are those that are so intense that they have a glowing effect in daylight. These pigments are added to various resins, ground up, and used as a pigment. Some fluorescent pigments are illuminated by an ultraviolet light source (black light).