Brown pigment non-removable, prevention and removal relate to which fixative and pigment?

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The issue here centers on the brown pigment that forms specifically when picric acid–containing fixatives are used, such as Bouin’s fixative. Picric acid can react with tissue components to create a picrate pigment that is brownish and binds strongly, making it difficult to remove with just water washes. The practical way to prevent or reduce this pigment is to use alcoholic washes, typically 50–70% alcohol, which helps dissolve residual picric acid and remove the pigment during processing. That’s why this option pairs a picric acid fixative with picrate pigment and alcohol washes as the preventive/removal method. Other fixatives produce different pigments and require different handling, so they don’t fit this specific brown pigment scenario.