- a dye, about litmus, this is certainly extracted from the lichen Rocella tinctoria; used as a microscopic stain so when a food colouring
- A reddish brown amorphous dyestuff, C7H7NO3, obtained from orcin, and creating the essential coloring matter of cudbear and archil. It's closely associated with litmus.
- A nitrogenous element (C7H7NO3) formed from orcine and ammonia.
Synonym for "orcein"
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