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• Colouration: The colouration must be relatively 1 Classification of dyes based on origin
permanent, not readily removed by rinsing in water a Natural dyes
or normal washing procedures, and must not fade
rapidly upon exposure to light. b Synthetic dyes
• Absorption: The process of attaching the dye 2 Dyes classification based on chemical structure
molecule to the fibre involves absorption, where dye a Azo dyes
molecules concentrate on the fibre surface. Four
kinds of forces bind dye molecules to the fibre: ionic b Anthraquinone dyes
forces, hydrogen bonding, Van der Waals’ forces, and c Triphenylmethane dyes
covalent chemical linkages.
d Phthalocyanine dyes
Dyeing of wool
e Quinoline dyes
Wool, a complex protein containing about 20 different
amino acids, undergoes dyeing in a dye bath where f Nitroso dyes
sulphuric acid forms ionic linkages with the amino g Indigoid dyes
groups of the protein. The sulphate anion is replaced
by a dye anion. In the dyeing of wool, silk, and synthetic h Natural dyes
fibres, hydrogen bonds are formed between various 3 Classification of dyes based on application
groups and the amino groups. Covalent chemical links method
are established in the dye bath by a chemical reaction
between a fibre-reactive dye molecule and a hydroxy a Direct dyes
group of a cotton fibre in the presence of alkali. b Reactive dyes

The chemistry of the dyeing process c Acid dyes
In any dyeing process, regardless of the chemical class of d Basic dyes
dye used, heat must be supplied to the dye bath. Energy
is used to transfer dye molecules from the solution to the e Disperse dyes
fibre and to swell the fibre, rendering it more receptive. f Vat dyes
This process is known as exhaustion.
g Pigments
Levelness: An important quality
4 Dyes classification based on solubility
Evenness of dyeing, or levelness, is an important quality
in dyeing natural and synthetic fibres. It can be attained by a Water-soluble dyes
controlling dyeing conditions, such as agitation to ensure b Oil-soluble dyes
proper contact between dye liquor and the substance
being dyed, and by using restraining agents to control c Solvent dyes
the rate of dyeing. Natural dyeing
Solvent dyeing Introduction
Recent consideration has been given to dyeing methods Dyes for textile dyeing can be divided into two main
where water is replaced by solvents like chlorinated categories, natural and synthetic dyes. Since prehistoric
hydrocarbons used in dry cleaning. Advantages of times natural dyes is used for coloring food substrate,
solvent dyeing include rapid wetting of textiles, less leather as well as fibers like wool, silk, and cotton. The use
swelling, increased dyeing speed, energy savings, and of non-allergic, non-toxic, and eco-friendly natural dyes
elimination of effluent (pollution) problems associated on textiles has become a matter of significant importance
with conventional dyeing and finishing methods. due to the increased environmental awareness to avoid
Machinery and equipment: Modern dyeing machines some hazardous synthetic dyes. At present synthetic
are made from stainless steel, with steels containing compounds are used for dying textile materials and they
up to four per cent molybdenum preferred to withstand cause water pollution as well as waste disposal problems
acid conditions. A dyeing machine consists of a vessel because these are non-biodegradable and carcinogenic.
to contain the dye liquor, equipped for heating, cooling, These problems can be solved by the use of natural
and circulating the liquor around the goods to be dyed or dye. Natural dyes, also known as natural pigments, are
moving the goods through the dye liquor. The choice of mainly derived from plant roots, stems, leaves, flowers,
machine depends on the nature of the goods to be dyed. fruits, animals, or natural-colored ores. Natural dyes are
colorants obtained from plants, invertebrates, insects,
Classification of dyes fungi, or minerals. Most natural dyes are vegetable
Dyes can be classified into various categories based dyes, the main sources of which are various parts of
on their origin, chemical structure, solubility, application plants such as roots, stems, seeds, barks, leaves, and
method, and other factors. Some common classification wood. There are also other biological sources such as
of dyes include: fungi, snails, insects, etc. Natural sources were the
main source of textile dyes before chemically dyeing.
Textile & Handloom: Shawl Weaving Artisan : (NSQF - 2024) R.T. Ex.No 1.6.55-65 81