Schmorl's method uses the reducing properties of melanin to stain granules blue-green. The most specific method of all is an enzyme histochemical method called DOPA-oxidase. It requires frozen sections for best results, but paraffin sections of well-fixed tissues may be used. Bleaching techniques remove melanin in order to get a good look at cellular morphology. They make use of a strong oxidizing agent such as potassium permanganate or hydrogen peroxide.
Ocular melanin takes hours to bleach, while that from skin takes minutes.
Formalin fixation imparts a strong yellow autofluorescence to unstained tissues with these substances. The pseudomelanin of melanosis coli is PAS positive whereas true melanin is not. Moreover, pseudomelanin pigment is usually found in macrophages. Lipochrome can be stained by Sudan black B, long Ziehl-Neelson acid fast, and Schmorl's methods. Lipochrome may also exihibit a strong orange autofluorescence in formalin-fixed, unstained paraffin sections.