Melanin is a non-hematogenous endogenous pigment, a group of pigments ranging in color from light brown to black, which are commonly found in the substantia nigra and hair follicles of the skin, eyes, and brain. Melanin has a remarkable physical property of being completely insoluble in most organic solvents. ---- This is almost certainly due to the fact that the melanin that has been formed in the melanosomes binds tightly to proteins, and that the melanin binds to proteins. Melanin binds to proteins and these complexes are called “melanin granules” in the cytoplasm. Another physical property of melanin is its ability to be bleached by strong oxidizing agents, although this process is slow, and in pathological cases this pigment can also be found in benign nevus cell tumors as well as malignant melanomas; a number of methods can be used to identify melanin and melanogenic cells, the most reliable of which are: reduction methods, such as the Masson-Fontana Silver Technique and the Schmörl Trivalent Iron - Potassium Ferrocyanide Reduction Assay; and the reduction of the melanocytes by the Schmorl Trivalent Iron - Potassium Ferrocyanide Reduction Assay. potassium ferricyanide reduction assays; enzymatic methods (e.g., dopa reaction); fluorescence methods; and immunohistochemistry.

Melanin staining solution (ferrous sulfate method) uses melanin to take up ferrous ions to form melanin ferrous complex, and then combines with potassium ferricyanide to produce blue ferrous ferricyanide under acidic environment, i.e. Teng's blue reaction, ferrous sulfate method is also known as ferrous ion uptake method, the staining solution is suitable for paraffin sections, and fixation is better by using formalin and should not be used in chromate fixation solution.