Archil

A natural dye that is bright red to rich purple color, obtained from any of several lichens of the genera Evernia, Roccella, Ramalina, and Lecanoria. such lichens were used by the Egyptians for dyes; the preparation of archil was rediscovered and monopolized by Federigo, an Italian, in the Middle Ages. Archil was used to make the brilliant reds and purples in Florentine cloth. In the18th century a Scottish chemist, C. Gordon, rediscovered and patented the process, which he called "cudbear." The dark red color in archil is formed when lecanoric acid is converted to orcein by fermentation then oxidation. Archil is used as a pigment, textile dye, wood stain, food colorant, and an indicator dye that turns blue in alkaline solutions.