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Basic concepts of colours and their impact on fabric

Basic concepts of Light and colour -

Colour normally visible to us is a combination of the effect of -
(1) Properties of the coloured substances.
(2) Properties of the light falling on it and getting reflected or transmitted.
(3) Properties of our eyes on which the reflected or transmitted light falls.

The sun is the main and most important source in our solar system. It emits energy in the form of light. 

The light travels in the form of waves at tremendously High velocity i.e 3*108 m/s.

















Only light with a wavelength between 400 and 700 nm is visible to the human eye out of all the light that makes up sunlight. 

The distribution of the wavelength of the radiation in the visible region of sunlight and their corresponding colours are given below. Light is electromagnetic radiation. 

Visible light and electromagnetic spectrum
Visible light and electromagnetic spectrum 

Colour and chemical constitution - 

Colour consist of two groups- 

(i) Chromophore and 
(ii) Auxochrome Explanation - 

(i) Chromophore - (colour-bearing group in dye structure)
Nature must be unsaturated for colour development. Coloured compounds have double bonds, while colourless molecules do not 

It is recognised that for compounds to be coloured, they must have unsaturated chemical groups known as chromophore or colour-bearing groups. 

Chromogen is a chemical that contains a chromophore, although it is not a real dye. 

Types of Chromophores -

(a) Dependent 
(b) Independent 



More than one colour or one Chromophore sufficient to impart colour Ex: N2, N2O, NO2

The single chromophore is sufficient to impart colour Ex: Ethene

(ii) Auxochromes - 

● Auxochromes, which are particular groups' contributions to colour deepening, or 
Auxochromes are particular colour-enhancing or colour-intensifying groupings. 
● Auxochromes aid in the development of colour but are not colour themselves.
● Auxochromes can be anionic or cationic and can be of the acidic or basic variety.

Several significant auxochromes are -

Ex: -OH,-SO3,-NHR,-NH2,-OSO3H,-COOH,-NR2
● Auxochromes form salts either with acids or Alkalies and also Hydrogen bonds with certain groups like the hydroxyl (-OH) group in cellulose and the amino(-NH2) groups in wool and silk.
● When the presence of chromophore in a substance is accompanied by an auxochrome, it becomes a dye.
● Ex: Azo-benzene containing only chromophore is not a dye but, when an -NH2 group is introduced it becomes p-amino azo benzene which is a dye.
In addition to chromophores and auxochromes, certain solubilizing groups like Sodium sulphonate may also be present in the dyestuffs.

The function of auxochromes -
(i)They increase the intensity of the colour
(ii)They make chromogen a dye which helps for fixing chromogen to the fibre

Types of Auxochromes -
(a) Batho-chrome or redshift
(b) Hypo-chrome or blue shift 

Batho-chrome or Redshift

Hypo-chrome or Blueshift

By incorporation of a certain group in di-molecule shifts the absorption maxima from a lower wavelength to a higher wavelength 

Any group when incorporated in a dye structure it brings changes in Absorption maxima from longer wavelength to shorter wavelength 

Groups that deepen the colour of dye or increase the depth of colour are known as Batho-chrome or redshift

It lightens or reduces the intensity of colour or decreases the depth of dye known as Hypo-chrome
and This phenomenon is known as Hypo-chromic shift or blue shift

Ortho and para position groups have to deepen the colour 

Ex: -OCH3, -OCOCH3

Meta position will decrease depending on the colour.

Acylation of phenolic group

Alkali, arile and halogens are Batho-chrome

Basic concepts of colours and their impact on fabric
Basic concepts of colours and their impact on the fabric

Questions -

  1. Describe concepts of colours.
  2. Which two groups are chemical colours contained?
  3. Explain Chromophore and Auxochrome colour groups.


Dyes and dyeing. (n.d.). from

eBook, T. (2021, February 22). Textile dyeing PDF by Dr. N. n. mahapatra. Textile EBook.

Introduction to dyeing and dyehouse automation. (2014). In Modelling, Simulation and Control of the Dyeing Process (pp. 1–30). Elsevier.

Rana, M. B. (2015). Textile dyes and their application process.

textile - Dyeing and printing. (n.d.). In Encyclopedia Britannica.

Textile dyes and dyeing. (n.d.). from

(N.d.-a). from http://chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/

(N.d.-b). from

(N.d.-c). from

(N.d.-d). from

Further reading,


 - Rushikesh Patil (Textile Engineer)
(DKTE Society textile engineering college Ichalkaranji)
Email Id -

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