A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber.

Both dyes and pigments appear to be colored because they absorb some wavelengths of light more than others. In contrast with a dye, generally a pigment is insoluble, and has no affinity for the substrate. Some dyes can be precipitated with an inert salt to produce a lake pigment, and based on the salt used they could be aluminum lake, calcium lake or barium lake pigments.

Dyed flax fibers have been found in the Republic of Georgia dated back in a prehistoric cave to 36,000 BP. Archaeological evidence shows that dyeing has been widely carried out for over 5000 years, particularly in India and Phoenicia. The dyes were obtained from animal, vegetable or mineral origin, with no or very little processing. So far the greatest source of dyes has been from the plants, especially roots, berries, bark, leaves and wood.