Which statement about mordants in hematoxylin staining is accurate?

• A. Only ammonium aluminum sulfate is used as a mordant
• B. Only ferric chloride is used as a mordant
• C. Ammonium aluminum sulfate and ferric chloride are mordants
• D. No mordants are used

Answer: (C)

In hematoxylin staining, a mordant is a metal ion that forms a complex with the dye, making it larger and insoluble so it binds strongly to tissue components like nuclei. The most common mordants used are aluminum-based salts and iron-based salts. Ammonium aluminum sulfate forms hematoxylin-aluminum complexes (often called hemalum) that produce a blue nuclear stain, while ferric chloride forms iron-hematoxylin complexes that give a dark blue to blue-black nuclear stain. Because both types of mordants are routinely used to enable and modify staining, the statement that both ammonium aluminum sulfate and ferric chloride are mordants is the accurate one.