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A reddish brown amorphous dyestuff extracted from certain species of lichen (e.g. orchella weeds).


It is derived from orcinol extracted from lichens (e.g. Rocella tinctoria). The orcinol is converted to orcein by reacting with ammonia and air.

It forms the essential colouring matter of cudbear (a commercial powdered archil). It is used as a food dye forming dark brown crystals. It is also used as a stain in microscopy to visualize elastic fibers.

Word origin: from its related chemical product: orcinol.
Synonym: archil, orchil, lacmus, litmus, Citrus Red 2, C.I. Natural Red 28.
See also: orcinol, orcin.