Azoic or naphthol dyes are formed in situ on the fabric through a coupling reaction of an aromatic alcohol or amine such as naphthol (the couplingcomponent) with a diazonium salt (the diazo component). Thedye formed contains an azo group:
The fabric is usually impregnated first with the aromatic coupling component followed by immersion of the fabric in a solution containing the diazo component,with the azoic dye being formed instantaneously. Owing to the instability of the components, the dyeings are carried out near room temperature. The dyes have moderate fastness, and dyeings may be mordanted to
increase fastness.
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