Dye:A coloured substance is known as dye when that can fixed upto the substrate and when fixed is not fugitive e.g. fast to light and not washable by water, dilute acid or alkali. Many natural dyes had been known and they were derived from both vegetable and natural sources. Now a day’s most of the dyes are synthetic and are prepared from aromatic compound. E.g. Coal-tar
Acid dye Na =Na+ +A- (coloured acid)
Basic Dye BCl =B+ (colored)
Dye or dyestuff: A dye or dyestuff is usually a coloured organic compound or mixture that may be used for imparting colour to a substrate in a reasonably permanent fashion. A dyed substrate should be resistant to a normal laundry or cleansing procedure and stable to light.
Optical brightness or whiteness which has the special properties of absorbing ultraviolet light and re-emitting the visible light to appear the substrate bright is called white dyes. They are colourless compound.
Dyes in a coloured substance but all coloured substance are not dyes. Thus a dye should fix itself on the substrate to give a permanent coloured appearance.
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Points of difference |
Dyes |
Pigments |
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They are soluble in water & most of the solvents |
Pigments are not soluble in water & most of the solvent |
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Available in large number |
Comparatively lesser in number |
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Lower as compared to pigments |
Very high |
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Low light fast |
more light fast |
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Dye molecules are comparatively smaller |
Pigment molecules are comparatively bigger. |
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Only can impart color by selective absorption of dyes |
Impart color by either scattering of light or by selective absorption |
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Usually the dyes are organic components |
They are normally inorganic components often involving very toxic |
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Dye fixation occurs throughout the cross-sectional area of leather |
Pigments only suspend on the surface of leather. |
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Temporary alter in the structure. |
They retain particulate or crystalloid structure. |
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