Tanned leather is (a) pretreated in an aqueous and alkaline medium either
with ammonia, primary amines or a mixture of ammonia and primary amines and then
with a polyfunctional organic compound containing at least one aldehyde group as
a functional group, or (b) in an aqueous and acidic medium with a polyfunctional
organic compound and then ammonia, primary amines or a mixture of ammonia and primary
amines, and (c) then dyed in an aqueous and alkaline medium with a water-soluble
dye containing at least one functional group which is capable of reacting with
one of the functional groups of the organic compound, forming a covalent bond.
A tanned and dyed leather is obtainable with a high color intensity, outstanding
wet fastness and excellent grain tightness, wherein the dye is permanently and
covalently bonded to the leather via a bridging group, preferably in the region
of the surface, and the bridging group is essentially bonded to the leather via
-NCH- groups.
