Azin dyes

Safranin (Safranin O or basic red 2) is a biological stain used in histology and cytology. Safranin is used as a counterstain in some staining protocols, colouring cell nuclei red. This is the classic counterstain in both Gram stains and endospore staining. It can also be used for the detection of cartilage, mucin and mast cell granules.

thumb|right|Letter from Perkin's son, with a sample of dyed silk Mauveine, also known as aniline purple and '''Perkin's mauve''', was one of the first synthetic dyes. It was discovered serendipitously by William Henry Perkin in 1856 while he was attempting to synthesise the phytochemical quinine for the treatment of malaria. It is also among the first chemical dyes to have been mass-produced.

Phenazine is an organic compound with the formula (C6H4)2N2. It is a dibenzo annulated pyrazine, and the parent substance of many dyestuffs, such as the toluylene red, indulines, and safranines (and the closely related eurhodines). Phenazine crystallizes in yellow needles, which are only sparingly soluble in alcohol. Sulfuric acid dissolves it, forming a deep-red solution.

chemical compound

thumb|Structure of a major component of the dye nigrosin. In staining dyes, nigrosin (CI 50415, Solvent black 5) is a mixture of black synthetic dyes made by heating a mixture of nitrobenzene, aniline, and hydrochloric acid in the presence of copper or iron. Related to induline, it is a mixture of phenazine-based compounds. Its main industrial uses are as a colorant for lacquers and varnishes and in marker pen inks. Sulfonation of nigrosin yields a water-soluble anionic dye, nigrosin WS (CI 50420, Acid black 2).