CREAM OF TARTAR ~ To change colour (PH indicator) and soften fibre
Cream of Tartar, also known as potassium bitartrate, is produced by fermenting grape juice. It is used to acidify the dye bath to effect a colour change, and in mordanting to soften wool fibers as well as slowing down the mordant uptake in a hot mordant bath.
In general Cream of tartar can be dissolved in the dye bath. It helps to lower the PH of the bath.
PH of Cream of tartar is 5.