We use Iron (ferrous sulfate) as a color changer, darkening or “saddening” natural dyes on protein or cellulose fibers. It also increases lightfastness and acts as a mineral mordant for dark shades. The famous black dye recipes from the 17th and 18th century use generous amounts of iron and tannin. Iron reacts with the tannin in many dyestuffs creating colors ranging from chartreuse green to black, depending on the dye it is combined with.
Our iron powder is light green and food grade. Too much iron can harshen the hand of protein (silk, wool) fibers, so use sparingly. Use it either during mordanting or in a post-dye bath. There are specific safety precautions with iron: Keep out of reach of children. Instructions on safe use are on our site here.
Ferrous Sulfate may also be used as the reducing agent in a traditional indigo fermentation vat, sometimes called the “Copperas” vat. Copperas is an older term for iron and this vat is best suited to cellulose fibers. As well, it is possible to create an iron acetate mordant by combining iron and acetic acid. This is another old, traditional recipe. People sometimes use it as a thickened solution to create black lines on printed fabric.
- 100g of Ferrous Sulfate is ample for creating many mordant or afterbaths at 1%