Iron hematoxylin, rather than aluminum hematoxylin, is usually used to stain nuclei in trichrome procedures because

• A. Subsequent staining solutions are basic
• B. Subsequent staining solutions are acidic
• C. Iron provides stronger coloration
• D. Aluminum causes overcolorization

Answer: (B)

In trichrome staining, you want the nuclei to stay distinctly colored while the rest of the tissue takes on the colors from the acidic post-stains. The following steps use acidic solutions, so the nuclear stain must resist acid decolorization. Iron hematoxylin forms a complex that is more acid-stable, keeping the nuclei dark and well-defined throughout the acidic staining steps. Aluminum hematoxylin, on the other hand, is more prone to fading or losing color under acidic conditions, which would blur nuclear detail. That compatibility with acidic subsequent stains is why iron hematoxylin is preferred.