Application of Indigo in dyeing

Cotton fabrics impregnated with grape-sugar solutions are printed with a mixture of finely divided indigo and strong caustic soda suitably thickened. On steaming the indigo white produced 

The diflieulties in this direction have also been to a certain extent Tanquished by the introduction of artificial indigo. A thickened mixture of orthonitrophenylpropiolic acid and grape-sugar, or better an alkaline xanthate with an alkali is printed, and the indigo blue developed by steaming and drying. 

However, orthonitrophenylpropiolic acid does not appear to have made serious competition with natural indigo in this direction, and interesting as the synthesis is from a scientific standpoint, it has not yet been applied practically to any great extent. 

Indigo carmine is almost exclusively used in wool-dyeing, and is applied in an alum bath at the boil. 

The shades obtained are finer than those from the vat, but are not so fast. They are principally used in production of mixed shades. 

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