Cream of Tartar (COT) – Cream of Tartar is a white powder often used in baking to help stabilize meringue. It is a byproduct from the sediment left behind in winemaking – another use for a waste product! In natural dyeing, we use cream of tartar to acidify the dye bath to as a color changer. It’s also used in mordanting to soften wool fibers. As well, I’ve read that it helps aluminum sulfate bind more strongly to the fibers. Depending on the dye, it will shift cochineal, madder and lac to brighter, redder colors. With madder, it will shift the hue to orange and with cochineal the color will become a bright red. It can inhibit the color development in logwoods and certain tannins, so we rarely use it with these dyes.
We can also use cream of tartar as an adjunct to mordanting wool. Its purpose is to assist the alum to bond with the wool and it also keeps wool fibers soft. Bear in mind that it will shift colors, and in some cases, can inhibit the development of certain shades.
CALCULATING THE AMOUNT OF MORDANT
The amount of cream of tartar should be 6% of the weight of fiber, or 1 1/4 teaspoons for 100 grams of fiber. You can use aluminum sulfate and COT together. The COT brightens many colors and helps keep wool fibers soft.