* The role of sequestering agents in reactive dyeing

Is the use of a sequestering agent required when dyeing with reactive dyes?

When the water of the dyebath contains metallic ions, there is the danger that uneven dyeing, such as specking, or reduction of the concentration of the dye will be caused by the dyestuff's coagulation and reduced solubility. Aside from in the water, metallic ions can also be introduced by impurities in Glauber's salt or common salt, so even when soft water is used in the dyeing, the presence of metallic ions can lead to problems. In Japan, the water quality is generally very good and the chemicals used contain very few impurities, so sequestering agents are often not used. Overseas, however, the use of sequestering agents is very important.
In the past, traditional thinking has been that "if the chromophore of a dyestuff is a metallic complex salt, then sequestering agents should not be used." Recently, however, it has been ascertained that sequestering agents added to the dyebath have practically no effect on the metal in the chromophore of the dye.
Sequestering agents effective in neutral to alkaline conditions are preferable, and agents combining the effects of sequestering agents with those of anionic surfactants and marketed for use with reactive dyes are now being developed.