This chapter discusses the historic and present-day techniques employed for colouration using indigo, the oldest known natural blue dye. It has been mostly used for dyeing the popular denim jeans. Fabrics for other fashionable garments are also dyed using indigo. In recent times, the use of plant-based indigo has been replaced by its chemically indentical counterpart. This chapter begins with an outline regarding indigo formation in plants so as to highlight the chemisty involved in converting insoluble indigo into its water soluble leuco-form by reduction. this reversible conversion is critical to bring about textile colouration because only this form can be absorbed by textile fibres. Next traditional indigo dyeing and priniting methods that evolved across the globe are briefly reviewed. This is followed by a discussion on present day industrial practices. the use of alternate chemicals in teh indigo colouration process with a focus on minimising undesirable effects on the environment is highlighted. Catering to the present trend that prefers the use of natural to manufactured raw materials, a comparison between the colouring effectiveness of natural and synthetic indigo is included.
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