A blue-black precipitate is seen on an H&E stained slide. This could probably be prevented in the future by:

• A. Filtering the hematoxylin
• B. Increasing the time in hematoxylin
• C. Using a stronger mounting medium
• D. Reducing the dehydration steps

Answer: (A)

Particulate matter in the hematoxylin working solution is the clue. When hematoxylin isn’t filtered, undissolved pigment or metallic complexes can be carried into staining and then appear as blue-black precipitates on the slide. Filtering the hematoxylin removes these solids before use, keeping the stain clear and preventing those deposits from forming on the tissue.

If you were to leave the stain unfiltered but increase the time in hematoxylin, you’d risk over-staining and potentially accentuating any existing precipitates, rather than preventing them. Using a stronger mounting medium won’t fix the precipitate issue, since the problem originates in the stain itself, not the coverslip mounting. Reducing the dehydration steps wouldn’t directly address the particulate in the stain and could compromise tissue morphology or overall staining quality.