How can the colour of the Dyes be altered?

The answer lies in the Modifiers. Colour modifiers like methyl or ethyl groups can actually alter the colour of dyes. They do so by altering the energy in the delocalised electrons. It has been found that by addition of a particular modifier there is a progressive alteration of colour. An example can be given for methyl violet series.

The following diagram explains what happens to the colour of the dyes when modifiers are added.

Step A: When no methylgroup is added the original dye Pararosanil as it is called is red in colour.


Step B: As Four Methyl groups are added the reddish purple dye Methyl Violet is got.


Step C: With the addition of more groups a purple blue dye Crystal Violet is obtained. It has in it six such groups.


Step D: Further addition of a seventh methyl group the dye that is got is called Methyl green.

What gives the Dyes Solubility and Cohesiveness?

The answer to this riddle lies in substance called Auxochrome. Moreover the Auxochromes has also the abilty to intensify colours. It is a group of atoms which attaches to non-ionising compounds yet has the ability to ionise. Auxochromes are of two types, positively charged or negatively charged.

Classification of Dyes

There are several ways for classification of dyes. It should be noted that each class of dye has a very unique chemistry, structure and particular way of bonding. While some dyes can react chemically with the substrates forming strong bonds in the process, others can be held by physical forces. Some of the prominent ways of classification is given hereunder.

• Organic/Inorganic
• Natural/Synthetic
• By area and method of application
• Chemical classification- Based on the nature of their respective chromophores.
• By nature of the Electronic Excitation(i.e, energy transfer colorants, absorption colorants and fluorescent colorants).
• According to the dyeing methods
  • Anionic(for Protein fibre)
  • Direct(Cellulose)
  • Disperse(Polyamide fibres)
• However the most popular classification is the one that is advocated by the US International Trade Commission. This system classifies dyes into 12 types.