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1 Level dyeing or equalizing acid dyes; Method 1
2 Fast acid dyes; A bath is set at 500C at point A with 4% Sulphuric Acid
(96%) and5% Glauber’s Salt and hydrous, maintain pH
3 Milling acid dyes;
2.5 to 3.5. At B add required amount to dyestuff.
4 Super-milling acid dyes.
Method 2
To promote felting in a woolen material, it is treated with
weak alkaline solution with considerable mechanical At A set bath at 50° with 2% Formic Acid (85%) and 5%
action. This process is called milling. Dyes of good Glaubers Salt anhydrous,
fastness to milling are essential to avoid colour bleeding pH 3.5 to 4.5. At B add required amount of dye.
during the process.
Once the bath reaches 75 to 90 min i.e., at C add 2%
Properties of acid dyes Sulphuric Acid (96%) or 2% Formic Acid (85%).
The solubilizing group present in acid dyes are sodium The fabric is rinsed thoroughly after dyeing to remove
salt of sulphonic acid and these form large anion in the any loose dye.
aqueous solution. The method of application of acid dyes to a fabric is by

The main properties of acid dyes are bringing about a chemical reaction. When the acid dye
is applied to the fabric a salt link is formed between the
• Acid dyes are water soluble
molecules of the dye and the polymers of the fabric. This
• Acid dyes are anionic in nature bond that is formed between the dye and the fabric is
• Application of acid dyes are from strong acidic what provides the colour to the fabric. The place at which
condition to neutral pH the dye and the fabric bond is known as the dye site and
in materials like wool, the dye sites are the amino groups
• Acid dyes have excellent affinity towards protein and in the fibre.
polyamide fibres like wool, silk and nylon, modified
acrylics. The types of acids that are used in the acid dye and its
applications are acetic acid, hydrochloric acid or sulphuric
• They are not suitable for dyeing cellulosic fibres acid and the best application is achieved on heating
because the dye lack affinity towards cellulosic fibres the dye acid mix. The heating process jump starts the
• The dye fibre bonding that normally occurs is by process of dying, which is not possible below the 40⁰c
hydrogen bond, Vander Waal’s forces and mainly point. A higher temperature gives a better dying result
through ionic bonding. as the heat enables the dye to separate from the acid
mix and join the polymer of the fibre. In cases, where
Methods of acids dyeing: There are two methods of acid dyes and its applications are used in the form of
dyeing the fabrics with acid dyes. The difference is the printing, it is possible to get the transfer done with the
use of different acids at different concentrations. (Fig 1) help of steaming.

The use of acid dyes on fibres is something that is most
result oriented, which is what makes the application of
acid dyes popular in the fabric industry. The fabrics dyed
with acid dyes are known to have excellent light fastness
in a lot of cases which is why the fabrics dyes with acid
dyes keep looking brighter for longer. However, when
you need to make sure that you have the most viable
results from the acid dying process, it is important to be
sure about picking the right manufacturer of acid dyes.

Textile & Handloom: Shawl Weaving Artisan : (NSQF - 2024) R.T. Ex.No 1.6.55-65 87