Orcein, also archil, orchil, lacmus and C.I. Natural Red 28, are names for dyes extracted from several species of lichen, commonly known as "orchella weeds", found in various parts of the world. A major source is the archil lichen, Roccella tinctoria.[1] Orcinol is extracted from such lichens. It is then converted to orcein by ammonia and air.
Orcein is also used as a stain in microscopy to visualize chromosomes, elastic fibers, Hepatitis B surface antigens, and copper-associated proteins.
Aceto-orcein stain turns chromosomes a purple-red colour. This stain can be prepared from powder or purchased as solution; staining is best with freshly prepared stain as, over time, the stain precipitates and changes colour from a deep red or burgundy colour to a brownish colou.
