Wednesday, December 30, 2009

Natural dyes classified on the basis chemical nature of colouring matter

Natural dyes can be classified on the basis chemical nature of colouring matter:-

The yellow colours are derivatives of hydroxy and methoxy substituted flavones or isoflavones. Eg: - jackfruit bark

The dyestuff is extracted from Indigofera tinctoria, a bush of the pea family. The dye is extracted from the leaves of the plant.

Dihydropyrane :-
These are principal colouring matters of logwood and they give dark shades on cotton, silk, and wool.

Some of the most important red dyes are based on the anthroquinone structure. These are obtained from both plants and insects. These dyes have good fastness to light. They form complexes with metal salts and the resultant metal–complex dyes have good Manjitha

Anthocyanidins: -
This class includes carajurin, obtained from the leaves of Bignonia chica and Awabanin. It dyes silk in blue shades eg. Beet Root

Carotenoid :-
This class includes the orange pigment carotene found in carrots. The dyes based on carotenoid structure are annatto and saffron.

Alpha-hydroxy naphthoquinones:-
The 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.

Author : Supriya Sagar Kanzarkar (SGGS I.E & T, Nanded)

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