Dyes
Although many different kinds of dyes may be used, most tie-dyers now dye with Procion MX fiber reactive dyes. This class of dyes works at warm room temperatures. The molecules permanently bind with cellulose based fibers (cotton, rayon, hemp, linen), as well as silk, when the pH is raised. Soda ash (sodium carbonate) is generally used to raise the pH and is either added directly to the dye, or in a solution of water in which garments are soaked before dyeing. They do not fade with washing, but sunlight will cause the colors to fade over time.
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