G. H. Friedman's differential staining techniques for calcium-bearing carbonates and gypsum (J. Sediment. Petrology v. 29, no. 1, p. 87-97, 1959) have been successfully applied to a wide variety of materials. Results are reported. Single grains and unconsolidated and consolidated materials, including coals, were tested. Clearly resolved differential staining was obtained even on the finest scale, regardless of the matrix.