PRO Washfast Acid Dyes & are designed to permanently dye protein fibers - animal fibers like wool, silk, angora, mohair, alpaca, soy silk, and nylon. They have excellent wash and light fastness properties. Available in over 100 vibrant and intermixable colors. These dyes must be fixed with an acid fixative. We recommend Amonium Sulfate (for pastel to medium shades) or Citric Acid Cystals (for pastel to dark shades). Acid dyes must be dissolved with boiling water and applied at a boil for solid shade dyeing and steam set when printing, hand painting or rainbow dyeing. Two ounces (58 grams) of dye powder will dye 12 pounds (5.5 kilograms) of wool to a medium shade.
Please Note: If you are dyeing feathers for hair expensions, DO NOT use directions for staining silk flowers and feathers. Those directions do not allow you to result in a feather that is waterproof. You will need to follow the Rainbow Dyeing directions, where the dye is applied with a brush and then steamed, in order for the color to be permanent.
Suggested Auxiliaries when using PRO Washfast Acid Dyes: 
Ammonium Sulfate or Citric Acid Crystals 
Common Salt or Glauber Salt 
Synthrapol SP, Synthrapol LF or PROsapol