Fuchsine acid (C.I. 42685)

Acid fuchsin or fuchsine acid, (also called Acid Violet 19 and C.I. 42685) is an acidic magenta dye with the chemical formula C₂₀H₁₇N₃Na₂O₉S₃. Acid fuchsin has wide use in histology, and is one of the dyes used in Masson's trichrome stain. This method is commonly used to stain cytoplasm and nuclei of tissue sections in the histology laboratory in order to distinguish muscle from collagen. The muscle stains red with the acid fuchsin, and the collagen is stained green or blue with light green SF yellowish or methyl blue. It can also be used to identify growing bacteria.