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Abstract

Mineral tanned leather is frequently retanned with synthetic tanning agents to improve the fullness and softness, but leather retanned by the prior art methods is difficult to dye in full shades with anionic dyes. According to the invention, condensation products of C.sub.1-4 aldehydes with certain aromatic sulfonic acids or carboxylic acids containing amino groups are employed for retanning, thereby improving the receptivity of the leather for anionic dyes. These acids have the general formula ##STR1## where X and X' are independently H, --CH.sub.2 --SO.sub.3 H or --CH.sub.2 --OH, A is a benzene radical, Y and Z are independently H, --SO.sub.3 H or --CO.sub.2 H, R is H or C.sub.1-4 -alkyl and n is from 0 to 10, with the proviso that at least one sulfonic acid or carboxyl group is present in the molecule.

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First Claim