The ferrous mordanting process used for bleaching pigmented fibers has been improved. The serious problems of discoloring and excessive damaging of bleached fibers associated with the deposition of iron during the mordant bleaching process are resolved. All mordanting parameters are critical for successful bleaching of pigmented fibers. When used at a specific temperature and a specific time during mordanting, a reagent (reductive agent or acid) capable of stabilizing the mordant bath (during treatment) produces the most complete reaction of melanin with the iron, while not allowing the iron to be deposited on the keratin. Thus, in the subsequent bleaching process, maximum whiteness is achieved with less damage in terms of the mordanting. Sodium bisulfite can be used as an auxiliary, i.e., at the initial 4.0 pH of the bath, and acetic acid and citric acid can also be applied during mordanting without causing discoloration and excessive damage. The optimum conditions for mordanting are 20°C and 15 minutes when sodium bisulfite is used, and 60°C and 15 minutes with a stabilizer of acetic acid or citric acid. The improved process is, in all respects, superior to conventional processes, with no need for after-treatment with a reducing agent.
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