Natural IndigoA.Indigo is a dark blue crystalline powder that melts at 390°–392°C.
Properties of Indigo
B.It is insoluble in water, alcohol, or ether but soluble in chloroform, nitrobenzene, or concentrated sulfuric acid.
C.The chemical structure of indigo corresponds to the formula C16H10N2O2.
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D.The naturally occurring substance is indican, which is colorless and soluble in water. Indican can easily be hydrolyzed to glucose and indoxyl.
E.Mild oxidation, such as exposure to air, converts indoxyl to indigo.
F.Indigo is a frequency range of visible light, from 440 to 420 nanometers in wavelength, placing it between blue and violet.
Indigo has despite many other blue dyestuffs kept his popularity. This by no doubt is achieved by the fact that Indigo has a number of properties which have in this combination not yet been achieved by other single dyestuffs.
The main properties are:
• Pleasant colour shade.
• Possibility to achieve by simple repeated dipping, deep marine blue shade.
• Possibility to dye cotton in cold dye bath.
• Competitive in price.
• Possibility to achieve an acceptable colour fastness and the exceptional advantage by repeated washing of fading colour, to keep the colour shade that always a clear, pleasant blue shade result.
Three basic steps for indigo application are .
1.Dissolving the dye by reduction involving vatting and loosening up.
2.Dyeing from the vat.
3.Oxidising in the air.
Since indigo has a low affinity for cotton, deep blue dyeings are only obtained when dyeing and oxidising are repeated several times.
Five major Indigo dyeing methods for the basic denim are
1- Indigo rope dyeing process
2- Indigo one sheet dye slashing
3- Indigo double sheet dyeing
4- Loop dye 1 for 6 (continuous dye slashing)
5- Loop dye 1for 6 with dyemer (continuous mercerization dyeing and sizing).
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