Iron (ferrous sulfate heptahydrate)
Price is per ounce.
Iron (ferrous sulfate heptahydrate) is used as a color changer, darkening protein or cellulose fibers. It can harshen the hand of protein fibers, so use sparingly, at no more than 4% on weight of goods. It can be used either during mordanting, in a post-dye bath, or in any application where a color change is needed.