Iron salts in the form of ferrous sulphate (also known as green vitriol or copperas)
are extensively used in dyeing and printing. Application of iron salts imparts a
black or grey color to the fabric and dulls the shade. Ferrous sulphate if applied
alone leaves only a very small quantity of iron on the fabric. Tannin-pretreated
cotton picks up a good amount of iron. Cream of tartar can be used along with iron
to fix it on the animal fibers. Traditional dyers use a fermented iron solution for
iron mordanting where iron is present as acetate.