Which pigment is removed by alcoholic picric acid?

• A. Acid hematin
• B. Mercury pigment
• C. Hemosiderin
• D. Lipofuscin

Answer: (A)

The main idea is differentiating and clearing pigment that can form during hematoxylin staining. Acid hematin is a brown-black pigment that appears when hematoxylin-treated sections are exposed to acidic conditions, which reduces stain contrast. Alcoholic picric acid selectively dissolves this acid hematin, improving nuclear detail by removing the unwanted pigment while leaving the true hematoxylin stain intact. The other pigments mentioned—lipofuscin, hemosiderin, and mercury pigment—are not targeted by this step, so they aren’t removed by alcoholic picric acid in the same way.