Masson's trichrome stain

Masson's trichrome is a three-color staining protocol used in histology. The recipes evolved from the original Masson's formulation to different specific applications, but all are suited for distinguishing cells from surrounding connective tissue.

Most recipes produce red keratin and muscle fibers, blue or green collagen and bone, light red or pink cytoplasm, and dark brown to black cell nuclei.

The trichrome is applied by immersion of the fixated sample into Weigert's iron hematoxylin, and then three different solutions, labeled A, B, and C:
 * Weigert's hematoxylin is a sequence of three solutions: ferric chloride in diluted hydrochloric acid, hematoxylin in 95% ethanol, and potassium ferricyanide solution alkalized by sodium borate. It is used to stain the nuclei.
 * Solution A, also called plasma stain, contains acid fuchsin, Xylidine Ponceau, glacial acetic acid, and distilled water. Other red acid dyes can be used, eg. the Biebrich scarlet in Lillie's trichrome.
 * Solution B contains phosphomolybdic acid in distilled water.
 * Solution C, also called fibre stain, contains Light Green SF yellowish, or alternatively Fast Green FCF. It is used to stain collagen. If blue is preferred to green, methyl blue, water blue or aniline blue can be substituted.

A common variant is Lillie's trichrome. It is often errorneously called Masson's trichrome. It differs in the dyes used, their concentrations, and the immersion times.