In dyeing, sodium carbonate is used as a fixer and scouring agent. It may be used in small amounts to alter the ph of a madder dye bath which causes it to redden, or used for scouring cellulose fibers. It is also an easy way to raise the pH of an indigo vat. (for balancing an indigo vat, plan on using between 250-500 grams (8-16 ounces) of soda ash.) In addition, it is a mild base that increases the pH of an indigo vat or adds alkalinity to a dyebath to modify its shade.