What is the correct sequence to remove Formalin pigment AFH from tissue?

• A. Bring section to absolute alcohol → Place section in saturated picric acid for 5 min to 2 hours → Wash for 15–20 min in running tap water → Proceed to desired stain
• B. Place section in saturated picric acid → Bring to absolute alcohol → Wash twice
• C. Wash in running tap water → Alcohol → Picric acid → Stain
• D. Alcohol → Acidified water → Picric acid → Stain

Answer: (A)

Formalin pigment AFH is removed most effectively after the tissue has been dehydrated so the pigment can be reached by the solvent. Dehydrating to absolute alcohol first enables the saturated picric acid in alcohol to solubilize and dissolve the pigment efficiently. Placing the section in saturated picric acid for a set time (5 minutes to 2 hours, depending on pigment amount) removes the pigment without overly disturbing tissue integrity. A thorough rinse in running tap water then eliminates both the picric acid and dissolved pigment, preparing the tissue for the chosen stain. Starting with picric acid before dehydration is less effective because the pigment isn’t as accessible; washing before the pigment-removal step won’t dissolve the pigment adequately; and introducing acidified water in between can alter pigment removal and staining outcomes.