Advancement in Indigo Dyeing

Indigo is one of the most globally widespread dyes of antiquity, and the history of indigo cultivation is closely associated with colonial Bengal. Indigo has a very low affinity for cellulosic, and hence, multiple dips and nips with intermediate air oxidation are required for gradual shade build-up. Sodium hydrosulphite, the most commonly used reducing agent, can generate a reduction potential of −700 mV to −1000 mV. The use of sodium hydrosulphite causes severe environmental concerns when released in industrial waste water due to its carcinogenic health effects. Hence, various ecofriendly reducing agents in the indigo dyeing process have been developed. The ubiquity of blue denim has sustained indigo's use within the ever-globalizing fashion industry. Today, there is growing interest worldwide in reviving the use of natural indigo on ecological grounds. Focus has also been given to indigo's chemical properties and its dyeing chemistry with cellulosic fibers. This chapter addresses different dyeing methods, such as ball/cable warp dyeing, slasher dyeing, loop dyeing, etc. Indigo recovery and reuse and getting uniform shade, equilibrium between the dyes and chemical is also discussed. Focus has also been given to the factors affecting indigo destructions and possible ways to prevent yellowing or ozone fading.