16: Dyeing Check Access

Dyeing leather is an important process, because visual perception is the first experience that a customer or anyone else has of the material: the colour itself, the intensity and the uniformity. Traditionally, vegetable-tanned leather was coloured by natural products, which required the assistance of a mordant. The development of chromium(III) tanning followed the development of synthetic dyes, which offered deeper shades. Currently, the commonest class of dyes for leather is the 1 : 1 premetallised dyes, the equivalent of a strong colourant carrying its own mordant. Other classes of dyes are also used, particularly 1 : 2 premetallised dyes for intensifying colour on the surface; if required, acid dyeing processes can be assisted by levelling agents or intensifying agents. For improved performance there are several versions of reactive dyes for covalent fixation via aromatic heterocycles. Sulfur dyes are used for leathers stable to high pH. New classes of dyes are being developed, notably from natural sources, e.g. from fungi.