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Methods for the mordant dye application

 Method of Application of mordant dye

Method of application of Mordant Dyes to wool are listed below:

(A) Chrome mordant process
(B) After the chrome process 
(C) Meta-chrome process

All three methods have their own merits and demerits. Following is the explanation of each method.

Moderant dye chemical structure

(A) Chrome Mordant Process: 

In this two-bath procedure, the sodium or salt solution is first to want to mordant the wool, which is subsequently coloured within the presence of sulphuric acid. 

The subsequent could be a basic explanation of the dyeing procedure. 

The material is first prepared, then placed during a mordanting bath containing 1–3% sodium bichromate, worked in, and then heated to 50°C for a brief time. 

To enable optimum metal absorption by the fibre, the bathtub temperature is raised to the boiling point and therefore the treatment is sustained for 60 to 90 minutes. 

The absorption is accomplished by adding 1-3% acid to the tub and treating the fabric within the acidified solution.

To prevent the danger of the cellulose component degrading, acid (80%) is substituted for vitriol when dying cotton/wool blends. 

The chroming process may additionally use additional reducing acids, like carboxylic acid, ethanedioic acid, etc. the first goal is to show the chromate into its oxide so the fibre material can quickly absorb it. the following chemical formulae are illustrated. 

Methods for the mordant dye application
Equations 1 and a couple of above explain decreased mordanting in contrast to Equation 3, which depicts unreduced mordanting. 
Because yellow CrO3 turns into green Cr2O3, a process that happens fairly unevenly, the mordanted wool features a yellowish hue and is extremely light-sensitive (and may be recognised by a change in colour of the mordanted material from yellow to green). uneven dyeing would arise from unequal mordanting. 

Squeezing, dipping, and dealing in an exceeding dye bath at 30–40 °C, or ideally at temperature, are all steps within the mordanted wool's dyeing process. 

The needed amount of dye, 1-3% carboxylic acid, and 5- 10% salt are all present within the dye bath. While the fabric is being worked within the dye bath, the temperature is gradually increased to a boil. 

The dyeing is then administered at a boil for 60 to 90 minutes. By adding 1% to twenty-eight sulfuric acid toward the conclusion of the dyeing, the dye bath is depleted. 

C counting on the material's composition and the levelling characteristics of the various dyes, the technique above is changed. 

For example, it's preferable to mix 5- 10% salt with 3-5% ammonium sulphate when working with colours that have an occasional levelling power. 

These substances may additionally be accustomed to dye-dense or intricately woven materials where dye penetration is challenging.

(B) After the chrome process: 

As the name implies, chroming comes after dyeing and is the second process. This procedure also requires two baths. 

Since the dyes are applied on mordanted material using the chrome mordant process, the dye faces dye penetration and levelling challenges. 

However, because the dyes are applied first within the after-chrome process, their low relative molecular mass and excellent migration capabilities allow them to quickly penetrate the fibre and migrate to assist in levelling. 

Shade matching, however, becomes harder because the verity (final) shade isn't visible until after the chroming stage. 

The procedure entails dyeing the wool first, followed by treatments with salt and vitriol. The dye bath is ready using the needed amount of dye solution, 3–5% ethanoic acid, and 5–10% salt. 

The dyeing process begins at 40–50°C, and over the course of 30–45 minutes, the temperature is raised to boiling. to attain levelling and the same shade, dyeing is sustained for an additional 45–60 minutes. 

By adding 0.5 to fifteen formic or acid and continuing the procedure at the boil for a further half-hour, the dye bath is also exhausted. the fabric is then removed, cleaned, and compressed.

The treated items are then placed in an exceeding bath containing 1-3% salt (plus acid, if necessary) at a boil for 30-45 minutes. 

The after-chrome method is primarily appropriate for dyeing medium and deep colours.

Chelation—a complicated bond between a dye molecule and a metal ion—occurs within the fibre in both processes, including chrome mordant and after-chrome, and as a result, level dyeing is produced by consistent initial treatments. 

However, both approaches take a protracted time, require plenty of labour, and are expensive because dyeing and mordanting are done separately, which needs additional water, steam, time, etc.

(C) Meta-Chrome process : 

The meta-chrome process simply entails one step, in opposition to the two-step processes mentioned above. 

The technique makes use of the benefit that chromium doesn't form lakes or complexes within the type of chromates, allowing the dyeing to be drained into the identical bath with ammonium sulphate. 

When dyeing woollen products at a boil, the progressive release of acid from ammonium sulphate encourages the transformation of chromate into dichromate.

The event of a lake occurs inside the fibre, which also absorbs the colour and chromium. The chemical reactions involved in the process are illustrated below. 


Methods for the mordant dye application

Due to the simplicity of administration and minimal damage to the fibre from the relatively brief treatment period, this method only requires one bath. 

Additionally, there's no shade dulling. The procedure's two main drawbacks are first, the poor rubbing fastness caused by complex formation within the bath, and second, the need that only colours that don't react with chromium to be used. 

The following chemicals are accustomed to setting the dye bath once the dyestuff has been dissolved in boiling water. 



X part

Sodium chromate

1 to 2%

Ammonium sulphate

2 to 3%(6 to 8% for deep shades)

To achieve the proper liquor ratio, the desired amount of water is used. 3-8% of the produced 1:2 mixture of chromate and ammonium sulphate is applied.

The material is submerged in a very dye bath that's kept at 50 degrees Celsius and worked certain 5 to 10 minutes. 

Over the subsequent 45 hours, the temperature is gradually raised until it reaches a boil. Dy For 60 to 90 minutes, dyeing is sustained at the boil. 

The coloured items are thoroughly cleaned and squeezed. Because they fade so quickly, mordant colours are especially challenging to get rid of. Correction of uneven colouring is thus a continuing challenge. 

When the dye-metal complex is attenuated, errors in dyeing will be fixed by boiling the dyed wool in a fairly strong oil of vitriol. 

After that, the colour that has been peeled is partially removed with a hot ammonia treatment. the things can then be coloured again. 

Disadvantages of Mordant Dyes

Mordant dyes are nowadays accustomed to a way less extent, for the subsequent reasons.

(a) Colour matching is challenging since the colour develops gradually during the mordanting process. 
(b) Prolonged processing times are expensive and additionally harmful to protein and polyamide fibre.
(C) When sodium and salt salts are released into the environment as dyeing effluent, they grow to be contaminants.

Questions -

  1. Which methods of dyeing are used for the mordant dye application?
  2. Explain Chrome's mordant process for dyeing.
  3. Explain After the chrome process for mordant dyeing.
  4. Explain the Meta-chrome process for mordant dyeing.


How to mordant. (2017, February 21). Botanical Colors.

Kennedy, L. (2020, October 30). Mordants for natural dyes - what you need to know. Little Yellow Wheelbarrow.

Mordants and fixatives - natural dyeing. (2012, September 3). All Natural Dyeing.

The MAIWA BLOG: Natural dyes - mordants part 1. (n.d.). The MAIWA BLOG. from

Victoria. (2020, November 18). The importance of using a mordant in natural dyeing. La Creative Mama.

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