Cream of Tartar – 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 color change, and in mordanting to soften wool fibers. It will shift the color of cochineal, madder and lac from their fuchsia and burgundy red shades to a brighter, redder colors. With madder, it will shift the hue to orange and with cochineal the color will become a bright red to orange. It can inhibit the color development in logwoods and certain tannins, so it is rarely used with these dyes.