Based on Color
Blue Dyes: Natural indigo, sulphonated natural indigo and the flowers of the Japanese “Tsuykusa”
Red Dyes: The colour index lists 32 red natural dyes. The prominent among them are madder (Rubia tinctorum L), Manjeet (Rubia cordifolia), Brazil wood/Sappan wood (Caesalpina sappan L), Al or Morinda (Morinda citrifolia L).
Yellow Dyes: Colour index lists 28 yellow dyes. Some of the important yellow dyes are, black oak (quercus velutina), tumeric (curcuma longa), and weld
(reseda luteola) and Himalayan rhubarb (rheum emodi).
Showing posts with label natural dye. Show all posts
Showing posts with label natural dye. Show all posts
Sunday, August 3, 2008
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.
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.
Tuesday, December 18, 2007
MERITS AND DEMERITS OF NATURAL DYES
ADVANTAGES OF NATURAL DYES: -
1) Health and safety aspects of natural dyes: Though all natural dyes are not 100% safe they are less toxic than their synthetic counterparts. Many of the natural dyes like turmeric, annatto and saffron are permitted as food additives. Many natural dyes have pharmacological effects and possible health benefits.
2) They are obtained from renewable sources.
3) Natural dyes cause no disposal problems, as they are biodegradable.
4) Practically no or mild reactions are involved in their preparation.
5) They are unsophisticated and harmonized with nature.
6) Many natural dyes have the advantage that even though they have poor wash fastness ratings, they do not stain the adjacent fabrics in the washing process because of the non-substantive nature of the dye towards the fabric. An exception to this is turmeric, which shows substantivity for cotton.
7) Natural dyes are cost effective
8) It is possible to obtain a full range of colours using various mordants.
LIMITATIONS OF NATURAL DYES
The limitations of natural dyes that are responsible for their decline are: -
Ø Availability
Ø Colour yield
Ø Complexity of textile dyeing process
Ø Reproducibility of shade
Besides these there are other technical drawbacks of natural dyes: -
These are: -
Ø Limited number of suitable dyes
Ø Great difficulty in blending dyes
Ø Non-standardized
Ø Inadequate degree of fixation
Ø Inadequate fastness properties except few exceptions
Ø Water pollution by heavy metals and large amounts of organic substances.
1) Health and safety aspects of natural dyes: Though all natural dyes are not 100% safe they are less toxic than their synthetic counterparts. Many of the natural dyes like turmeric, annatto and saffron are permitted as food additives. Many natural dyes have pharmacological effects and possible health benefits.
2) They are obtained from renewable sources.
3) Natural dyes cause no disposal problems, as they are biodegradable.
4) Practically no or mild reactions are involved in their preparation.
5) They are unsophisticated and harmonized with nature.
6) Many natural dyes have the advantage that even though they have poor wash fastness ratings, they do not stain the adjacent fabrics in the washing process because of the non-substantive nature of the dye towards the fabric. An exception to this is turmeric, which shows substantivity for cotton.
7) Natural dyes are cost effective
8) It is possible to obtain a full range of colours using various mordants.
LIMITATIONS OF NATURAL DYES
The limitations of natural dyes that are responsible for their decline are: -
Ø Availability
Ø Colour yield
Ø Complexity of textile dyeing process
Ø Reproducibility of shade
Besides these there are other technical drawbacks of natural dyes: -
These are: -
Ø Limited number of suitable dyes
Ø Great difficulty in blending dyes
Ø Non-standardized
Ø Inadequate degree of fixation
Ø Inadequate fastness properties except few exceptions
Ø Water pollution by heavy metals and large amounts of organic substances.
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