Iron – Ferrous Sulfate

Iron – Ferrous Sulfate can be used alone as a mordant or to ‘sadden’/deepen or shift color.  It can increase lightfastness as well, and is used in some types of indigo vats as a reducing agent.  You can add iron directly to your dye bath or use it as an after-bath to shift the color.  As little as ¼ tsp is needed to change the color dramatically. 

Iron can be used with tannins to produce dark browns or grays, and used with yellows to produce olive greens.  Used with red producing natural dyes, it can give purples.