Which reagent can be used to remove formalin pigment?

• A. Alcoholic picric acid
• B. Iodine
• C. Sodium hypochlorite
• D. Water

Answer: (A)

Formalin pigment is a brown‑black deposit that can form in tissues fixed with formalin and interfere with staining. The most effective way to remove it is with alcoholic picric acid. The pigment dissolves in this solvent because the alcoholic picric acid solution can solubilize the pigment without markedly damaging tissue morphology or later stains. The other options don’t remove it reliably: iodine doesn’t dissolve the pigment, water won’t affect it, and sodium hypochlorite can bleach pigments but may damage tissue and staining patterns. Using alcoholic picric acid clears the pigment so the true histology can be evaluated.