CLASSIFICATION OF NATURAL DYES

Based on chemical structure:
Indigoids: -
The dyestuff is extracted from Indigofera tinctoria, a bush of the pea family. The dye is extracted from the leaves of the plant.
Anthraquinones: -
Red dyes are based on anthraquinone structure. These dyes are characterized by good fastness to light.
Alpha napthaquinones: -
Lawsone or Henna is the most prominent member of this class. It is obtained from the leaves of Lawsonia inermis. Another similar dye is Juglone obtained from the shell of unripe walnuts.
Flavones: -
The yellow colours are derivatives of hydroxy and methoxy substituted flavones or isoflavones. Eg: - jackfruit bark
Dihydropyrans: -
These are principal colouring matters of logwood and they give dark shades on cotton, silk, and wool.
Anthocyanidins: -
This class includes carajurin, obtained from the leaves of Bignonia chica and Awabanin. It dyes silk in blue shades.
Carotenoids: -
This class includes the orange pigment carotene found in carrots. The dyes based on carotenoid structure are annatto and saffron.

Fastness of Dyed Textiles

Dyeing is defined as an operation or a series of operation by means of which uniform color of permanent character is produced on a substrate. This implies that it should not be possible to wash the color out easily in laundering, nor should it fade rapidly when exposed to light. There is probably no dye, which can be guaranteed not to alter shade under all condition. Wide variation in the fastness properties of dyes are observed on number of factors, e.g. chemical constitution of the dye, nature of substrate, method of application, auxiliary chemicals added during dyeing etc.
A number of tests are necessary to cover all the important properties of any one dye because good fastness to one influence is not necessarily accompanied by equal fastness to exposure to other condition.Tests may be divided into those of customer significance, such as light, wash; perspiration, rubbing, sublimation and hose concern only the unshrinkable treatment, carbonization etc.