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Solubilised Vat Dyestuffs

Solubilised Vat Dyestuffs

The vat dyestuffs, which are unmatched for their overall fastness qualities, are inherently challenging to use with cellulosic fibres. 

(i) The challenges include the necessity for careful chemical control when converting insoluble vat colour to its leuco-compound,
(ii) the leuco-extreme compound's high affinity under typical dyeing conditions, which tends to supply uneven dyeing, and
(iii) challenges when oxidising the leuco-compound back to the insoluble vat colour.

Because they're water-soluble, have a way lower affinity for the fibre, and more easily change into the insoluble vat colour after dying, the solubilized vat dyestuffs are developed from vat dyestuffs that don't have these defects.

Since most solubilized vat dyes have such a weak affinity for cellulosic fibres, producing deep shades with them using conventional methods isn't cost-effective. I

nstead, padding processes are typically employed when producing deep shades with solubilized vat dyes. 

The solubilized vat dyes are particularly appropriate for pale colours that are challenging to urge with the traditional vat dyes. 

The 2 series of dyestuffs, vat dyes and solubilized vat dyes, are therefore discovered to enhance instead of competing with each other. 

Chemistry of solubilised vat dyes:

The solubilised leuco-vat dyestuffs come from the anthraquinonoid and indigoid vat classes similarly together or two parent vat colours that aren't suitable to be used as vat dyestuffs. 

They're also available as vitriol esters. After being absorbed by the cellulose, the esters are oxidised in an acid solution to revive them to their original, insoluble vat colour.

The solubilized vat dyestuffs are marketed as stable powders that ought to not be exposed to light, acid fumes, moisture, or high temperatures because these elements promote the deterioration of the colours.

The figure following shows the link between the appliance of a vat colour and its solubilized vat derivative. 

Chemistry of solubilised vat dyes


Dyeing cotton with solubilised vat dyes:

In water with sodium carbonate at a 50–70°C temperature, solubilized vat dyestuffs dissolve. 

Alternatively, the fabric could be padded through the answer rather than being coloured during this solution as normal.

The dyed material is then developed, or the parent vat colour is renewed, by treating it concurrently with an acid (often sulfuric acid) and an oxidising agent, which is acid, produced by the reaction of nitrite and oil of vitriol. oil of vitriol and nitrite are frequently added to the dyeing bath and therefore the developing bath, respectively.


The material is rinsed and soaped in the manner typically used in applying vat dyestuffs after the initial vat dye's development, or regeneration, The table below shows the order of operations.

Steps : 



The solubilized vat dyes' affinity for one dye compared to a different varies greatly. 

Typically, salt is added to the dye bath to reinforce tiredness. 

Padding techniques are popular (salt is eliminated during this case) and have the advantage of continuous operation. 

The ease of development differs from dye to dye, thus the amounts of nitrite and acid, additionally because of the temperature of development, must be tailored to every situation.   

The solubilized vat dyestuffs are typically utilised for pale hues because of their relatively low affinity. 

They're of very high value for the creation of sunshine shades with exceptional evenness and penetration on every kind of yarn and product. they're especially employed in garments like shirts, sheets, towels, knitted cotton, linen dress items, and for over-dying coloured-woven styles where fastness is crucial. 

Additionally, the dyeing of sunshine hues on polyester cotton, like for shirts, sheets, etc., has been done using soluble vat dyes. 

Cotton and polyester fibres will both be stained to an identical extent by soluble vat dyes at light colour depths, providing the looks of firmness of shade. 

It should be emphasised that, in terms of both light and wet fastness qualities, a properly processed solubilized vat dyeing is simply as quick as a standard vat dyeing performed with the parent vat dyestuff.

Questions -

  1. Explain dyestuffs of solubilized vat dye.
  2. What is the chemistry of solubilized vat dye?
  3. How dye the cotton with solubilized dyes?


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.

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

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