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. Perl's iron stain is the classic method for demonstrating iron in tissues. The section is treated with dilute hydrochloric acid to release ferric ions from binding proteins.
Mercurial fixatives seem to do a better job of preserving iron in bone marrow than formalin.
VonKossa stain is a silver reduction method that demonstrates phosphates and carbonates, but these are usually present along with calcium. This stain is most useful when large amounts are present, as in bone. Alizarin red S forms an orange-red lake with calcium at a pH of 4.2. The alizarin method is also used on the Dupont ACA analyzer to measure serum calcium photometrically. Azan stain can be used to differentiate osteoid from mineralized bone.