Common names for the lichen Ochrolechia tartarea L., Lecanoraceae and for the coloring matter from this and other lichens, especially Lecanoraceae and Roccellaceae. A source of litmus, q.v. Acids in lichens (e.g. lecanoric acid) hydrolyze to orcinol, q.v., which, in the presence of ammonia can be oxidized to the dye orcein, q.v. The dyes French Purple, Persio, Orchil, and Orseilles derive from the salts of orcein: Colour Index Vol. 3 (3rd ed., 1971) p 3241.