To minimize formation of formalin pigment, which action is recommended?

• A. Raise pH above 6.0
• B. Lower pH
• C. Add more formalin
• D. Decrease temperature

Answer: (A)

Formalin pigment forms when formaldehyde reacts in an acidic environment with heme to produce an insoluble hematin-type pigment. Keeping the fixative buffered at a neutral to slightly basic pH prevents these conditions, so raising the pH above 6—ideally around neutral (pH 7)—greatly reduces pigment formation. In contrast, lowering pH promotes pigment formation, adding more formalin increases available formaldehyde for reaction, and lowering temperature only slows the process rather than preventing it if the environment remains acidic.