Tartaric acid white crystalline organic acid. It can be used to shift the color of natural dyes like brazilwood and logwood. It is an optional addition to the alum mordant in the natural dyeing of cloth. It is used to soften the protein fibers and brighten shades. It is used like cream of tarter but will give different shades than cream of tarter. (Cream of tarter is the salt of Tartaric Acid. See our Twenty Ancient Dyestuff tech sheet for info.