Hematoxylin may form precipitates or films when in solution that can become deposited onto histologic sections.
Appearance: blue/black/purple precipitates of various sizes throughout the histologic section
Recognition:
(1) disappearance after filtering or replacing the hematoxylin solution
(2) exclusion of other causes of pigmentation or precipitates
Risk factors for precipitate formation:
(1) inferior quality of hematoxylin
(2) hematoxylin used after the expiration date
(3) hematoxylin solution after improper storage or handling
(4) failure to filter the solution before use
(5) formation of a surface film during the day
