Ferrous sulfate or iron is an optional mordant and is used as a color changer. It has the added benefit of making naturally dyed colors more light and washfast. It is more often used with cellulose fibers like cotton, linen, rayon and hemp and should be used with care on protein fibers as it can make them slightly hard or brittle. Iron shifts a color to a deeper, darker shade. If used in the mordant process that shift is more distinct than when used directly in the dyebath. Iron should be used at 2-4% wof. More than that could damage the fiber.
Natural dye – mordanting and nuancing any fibers : iron is the basis of all grey and black shades by reaction with natural tannins. In a general way, it is used to darken colors and make them deeper. It slightly improves light- and wash-fastness from those obtained with aluminum mordants. Recommended use at 1-3 % of the Weight Of Fiber (WOF). A higher % may alter the structure of proteinaceus fibers and make them breakable.
For grey and black shades, we also recommend to use our extracts of logwood, oak gallnut, sumach gallnut, tara, acacia. The best results will be obtained with combinations of these extracts.
Also, combinations of aluminum and iron mordants or a last (very light) iron bath after a aluminum-mordanted-color will widely increase the number of shades.
Iron gall inks: The iron sulfate is the basis of this historical ink where it is associated with tannins, in particular our very rich gallnut extracts from oak or sumach.