Pigment

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(Redirected from Pigmentation)

For the drug referred to as "pigment," see black tar heroin.

In biology, pigment is any material resulting in colour in plant or animal cells which is the result of selective absorption. Some biological material has so-called structural colour, which is the result of selective reflection or iridescence, usually done with multilayer structures. Unlike structural colour, pigment color is the same for all viewing angles. Nearly all types of cells, such as skin, eyes, fur and hair contain pigment. Butterfly wings typically contain structural colour, although many of them contain pigment as well. Creatures that have deficient pigmentation are called albinos.

Because pigment colour is the result of selective absorption, there is no such thing as white pigment. A white object is simply a diffuse reflecting object which does not contain any pigment.

In the coloring of paint, ink, plastic, fabric and other material, a pigment is a dry colorant, usually an insoluble powder. There are both natural and synthetic pigments, both organic and inorganic ones. Pigments work by selectively absorbing some parts of the visible spectrum (see light) whilst reflecting others.

A distinction is usually made between a pigment, which is insoluble, and a dye, which is either a liquid, or is soluble. There is a well-defined dividing line between pigments and dyes: a pigment is not soluble in the vehicle while a dye is. From this follows that a certain colourant can be both a pigment and a dye depending on in which vehicle it is used. In some cases, a pigment will be made by precipitating a soluble dye with a metallic salt. The resulting pigment is called a "lake".