Orcein is an organic dye that is commonly used in histology and staining techniques. This substance is also referred to as C.I. 14070, orchil, or litmus. Orchil is a purple or violet dye derived from lichens, while litmus is a pH indicator that changes color when exposed to acidic or basic solutions. Other synonyms for orcein include cloth purple, orchil red, and Spanish leather dye. It is also called "cudbear", after the name of the lichen from which it is extracted. Orcein is primarily used for staining biological materials like chromosomes and connective tissues, and can also be used in textiles and hair dyes.