Dyeing processes with indigo

In this section, the use of a wall-jet electrode (with optimal values for its parameters as described in section6.7.2) and the method to detect simultaneously sodium dithionite, sulphite and indigo (see section6.7.4) are evaluated as a function of reproducible dyeing processing. In order to evaluate this, a spectrophotometric method was used to measure the amount of dye absorbed and/or adsorbed by the dyed fabric. 

In a specially designed process, warp yam dyeings with indigo can be imitated [79],... 

The leuco-form of purple is light-sensitive. This property is associated with stepwise debromination, which means that the fraction of indigo and thereby the blue component can be distinctively different, depending on the dyeing process. 

Synthetic dyes, such as indigo with different concentrations (20%-8o%), alizarin for red, auramine for yellow, naphthol for red and yellow, and aniline for blue or black color, have replaced the traditional natural dyestuffs [1, 2, 4, 6]. Examples of the synthetic dyes used in batik processing are Brenta Soga produced by ICI, Naphthol as produced by Bayer, and Anthrasol produced by Hoechst [4]. 

Vat Dyes. Vat dyes are insoluble in water. Indigo, for example, an ancient blue dye, is probably the best-known example of an ancient vat dye others include woad and Tyrian purple. Since the process of dyeing requires that the dye be in solution, dyeing with a vat dye (or vat dyeing, as the process is known) is possible only after the vat dye has been made soluble by a relatively long and somewhat complicated chemical procedure. The terms vat dye and vat dyeing are probably derived from the large tanks or "vats", in which the process was carried out in ancient times. 

The special requirements of the indigo dyeing of cotton warp yarns for denim are capable of being met by indirect electrolysis systems [241]. Examples of four suitable redox systems are shown in Table 12.37. Uniform build-up of depth was observed with each successive step, the results being at least equal to those from the conventional dithionite-based process. Apparendy these processes are amenable to scaling up to bulk production levels [241]. 

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