Dyes are substances capable of imparting color by chemically or physically binding with materials (including biological tissues). Dyes are themselves colored due to absorption of various wavelengths of light. As an example, picric acid absorbs short wave-length light from the spectrum to transmit light perceived as yellow, while acid-fuchsin absorbs light from the middle of the spectrum to transmit light perceived as red.
Dyes can be grouped into the following two classifications:
Natural: Dyes that are derived from natural resources. The most important natural dyes in the histopathology laboratory are hematoxylin and cochineal (from which carmine is extracted).
Artificial: Dyes that are derived through chemical reactions. Artificial dyes greatly outnumber natural dyes.
