Archil, Or Orchil, (Span. orchilla; Fr. or-seille). The red, violet, and blue colors which are known in commerce under the names of archil, cudbear, and litmus are supplied by different species of lichens, rocella, variolaria, lecunora. The rocella tribe grow upon rocks on the seacoast in the Canary islands, Sardinia, and Corsica, at the Cape of Good Hope, and on the W. coast of South America. Archil is prepared by digesting the lichens in a hot solution of ammonia, allowing it to stand for a few hours, and exposing the clear solution, which is drawn off from the lichen, in deep jars, to the air for about three weeks; the solution when concentrated by evaporation forms the archil liquor of commerce. The dye is also met with as a violet paste, and when dissolved in alcohol is used to color spirit thermometers. In consequence of its want of permanence, archil is rarely employed with any other view than to modify, heighten, and give lustre to other colors. - Some confusion exists in reference to the trade names of the different dyes prepared from lichens, but the best authorities confine the use of the word archil to the liquid or pasty dye obtained from the rocella tribe.

Cudbear is the equivalent of persio, and is chiefly made from the lecanora tartarea, while litmus is derived from the rocella tinctoria.