The Role of Mordants in Fixation of Natural Dyes

Abstract

In a majority of cases, natural dyes exhibit insufficient affinity for substrates as well as poor fastness to light, washing, and crocking (rubbing). A common remedy for this is to use mordants, which may be applied before, during, or after the coloration step in processes termed pre-, meta-, and post-mordanting, respectively. In traditional processes, the mordants applied were plant extracts, minerals, or human and animal waste, but that range has widened in modern times. It now includes a range of metal salts, organic substances, and biopolymers. Strategies have also evolved of modifying the dyes and/or substrates, and to modify the dyeing process for example by use of electromagnetic and ultrasound irradiation. This chapter provides a review of all these aspects.