Different methods of softening nail specimens for histologic sectioning were compared. For nails of normal thickness, several methods were equally effective, namely, soaking in potassium hydroxide or nitric acid after fixation in formaldehyde solution or Polysorbate 40 (Tween 40) treatment of normally processed paraffin blocks. For thick nails treatment with polysorbate 40 was preferred, although potassium hydroxide was adequate.
Lewin K, DeWit SA, Lawson R. Softening Techniques for Nail Biopsies. Arch Dermatol. 1973;107(2):223-224. doi:10.1001/archderm.1973.01620170035010