Sodium chloride is mainly used in the dyeing process in printing and dyeing factories to promote or slow dyeing. For example, when dyeing cotton with direct dye, adding sodium chloride can promote the combination of dye and fiber and increase the dye uptake rate. When dyeing wool or silk with acid dyes, sodium chloride can be used as a dye retardant to slow down the adsorption speed between the dye and the fiber, improve the level of dyeing, and prevent the dyeing of flowers.