formalin pigment

for·ma·lin pig·'ment

a pigment formed when acid aqueous solutions of formaldehyde act on blood-rich tissues; characterized by rotation of the plane of polarized light, withstanding extraction in aqueous and lipid solvents, being bleached in acids and hydrogen peroxide; not formed when tissue is fixed with formaldehyde buffered to pH levels higher than 6.

for·ma·lin pig·ment

(fōr'mă-lin pig'mĕnt) A pigment formed when acid aqueous solutions of formaldehyde act on blood-rich tissues.