INDUSTRIAL CHEMISTRY ORGANIC CHEMISTRY A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z                    HOME ABOUT CATEGORIES SITE MAP COPYRIGHT ADVERTISE CONTACT entire Web this site dye Natural dyes from (A) birch: (1) leaves with alum mordant, (2) bark, (3) bark with iron mordant, (4) bark with alum mordant; (B) lichen (Lecanora tartarea) A colored substance which imparts its color to textiles to which it is applied and for which it has a chemical affinity. Dyes differ from pigments in being used in solution in an aqueous medium. Dyeing was practiced in the Fertile Crescent and in China by 3000 BC, using natural dyes obtained from plants and shellfish. These were virtually superseded by synthetic dyes – more varied in color and applicability – after the accidental discovery of mauve by Perkin (1856). The raw materials are aromatic hydrocarbons obtained from coal tar and petroleum. These are modified by introducing chemical groups called chromophores which cause absorption of visible light (see also color). Other groups, auxochromes, such as amino or hydroxyl, are necessary for substantivity – i.e., affinity for the material to be dyed. This fixing to the fabric fibers is by hydrogen-bonding, adsorption, ionic bonding, or covalent bonding in the case of "reactive dyes." If there is no natral affinity, the dye may be fixed by using a mordant before or with dyeing. Vat dyes are made soluble by reduction in the presence of alkali, and after dyeing the original color is reformed by acidification and oxidation; indigo and anthraquinone are examples. Dyes are also used as biological stains, indicators, and photography. See also azo compounds, fluorescein, and ink. Related categories    • INDUSTRIAL CHEMISTRY    • ORGANIC CHEMISTRY Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) BACK TO TOP