Depending on the supply, the current stock may be in granular form or powder form. Stock may be mixed. Iron is used as a color changer, darkening natural dyes on protein or cellulose fibers and also increases lightfastness for dyes that are prone to fading. Many of the famous black dye recipes from the 17th and 18th century use generous amounts of iron and tannin to produce rich black and gray colors. This particular iron powder is light green. Too much iron can harshen the hand of protein (silk, wool) fibers, so use sparingly. It can be used either during mordanting or in a post-dye bath. Keep out of reach of children. Ferrous Sulfate may also be used as the reducing agent in a traditional indigo fermentation vat, often called the Copperas vat. Copperas is an older term for iron or ferrous, and this vat is best suited to cellulose fibers, not for wool or silk. As well, it is possible to create an iron acetate mordant by combining iron and acetic acid. This is another old, traditional recipe.
