In the process of powdered indigo dyeing,it is necessary to use a lot of insurance powder and caustic soda for reduction,which has an adverse effect on the environment and the color of the cloth.The pre-reduced liquid indigo was prepared by the reduction of indigo with hydrogen.The normal dyeing could be done by adding a small amount of insurance powder and caustic soda.The pre-reduced liquid indigo and pow-dered indigo were used to keep the same indigo concentration in the dye solution,and dyeing was carried out at the reduction potential from-700 mV to-800 mV to analyze the chromaticity characteristics and color fast-ness of the dyed cloth.The results showed that the dyeing depth and color fastness of pre-reduced liquid in-digo could achieve the dyeing effect of powder indigo.The red color light was weaker than powdery indigo,which was more in line with the market trend.
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