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Introduction of Indigo dyeing

Indigo Dyeing

The plants that produce indigo are members of the genus Indigofera, and when exposed to air, the yellow liquid that's produced by their leaves quickly turns blue.

Indican, a glucoside of indoxyl that's hydrolyzed by enzymatic action into indoxyl and subsequently converted into indigo through further oxidation, is the plant's present source of colour.

In fact, indigo is also considered a dye for wool instead of cotton because it was first accustomed colour wool. 

The natural indigo plant's fermenting fluids were first accustomed to dye wool by early man some 4,000 years ago. 

The strategy was further improved over the years, and far later, around the year 1500 AD, cotton was dyed using it. 

Indigo dyeing

The reaction of Indigo with Cellulosic fibre:

Indigo must be chemically transformed into a soluble "leuco" form to be ready for dyeing because it's a kind of dye that's insoluble in water.

A vat dye's leuco form could be a distinct colour from the parent ingredient; indigo's leuco form could be a light yellow. 

Once the cotton yarns have absorbed the leuco kind of the dyestuff, they're either exposed to air or are treated with an oxidizer like peroxide to oxidise them and return the colour to its original insoluble form. 

The leuco variety of indigo incorporates a lower affinity for cotton than other vat dyes, therefore the yarn must undergo multiple dye application cycles to urge a sufficiently deep colour.

The cotton material must first be pre-wetted or boiled off by running it through hot and cold water baths containing surfactants to extend its absorbency. 

Industrial dyeing of denim warps typically involves either ball-warp dyeing or open-width dyeing (also referred to as slasher dyeing) (rope dyeing). 

Indigo's colour intensity is usually influenced by the number of dips, but other process factors, like dye concentration, pH, reducing agents, wetting agents, temperature, immersion time, and oxidation time, even have a control on the ultimate colour yield. 

These factors affect the quantity of indigo dye that accumulates on the material further as its penetration level. 

Surface dyeing or ring dyeing typically leads to a better apparent yield and better wash-down properties. 

Following may be a summary of this dye's overall reaction.
Reaction : 

Soluble leuco form of indigo
Soluble leuco form of indigo

Questions -

  1. Explain the process of indigo dyeing.
  2. What is the reaction of indigo dye with cellulose fibres?


Hussain, T. (2007, November 19). Important considerations in dyeing with vat dyes.; Fibre2Fashion.

Kim, M. R., Kim, H., & Lee, J. J. (2013). Dyeing and fastness properties of vat dyes on meta-aramid woven fabric. Fibers and Polymers14(12), 2038–2044.

Patwary, E. M. Z. (2012, May 4). What is vat dye. Textile Fashion Study; Engr. Mohammad Zillane Patwary.

Saha, S. (2018, October 21). Vat Dyes. Blogger.

Sharmin, F. (2017, November 18). Dyeing of cotton with vat dye. Textile Study Center.

The Editors of Encyclopedia Britannica. (2015). vat dye. In Encyclopedia Britannica.

  • More about denim fabric and indigo dyeing

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Writer - Rushikesh Patil (Textile Engineer)
(DKTE Society textile engineering college ichalkaranji)
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