Iron (Ferrous Sulphate) can be used in natural dyeing as either a mordant, to fix colour to fibre, or as a modifier, to change the tone of a naturally dyed colour. When iron is used with natural dyes, it tends to "sadden" the colours, or darken them towards grey/brown.
In the samples in the last image, the top row was mordanted with iron, while the bottom row was mordanted with alum (another mordant used to brighten colours). Each column is dyed with the same plant; from left to right, marigold, cochineal, and madder root.
Most natural dyes need to be used along with a mordant in order to help the colour attach to the fibre.
Available in 20g or 40g quantities in recycled paper envelops.
Use iron at 2% of the dry weight of fibre (WOF). (Eg. For 100g of fibre, use 2g alum.)
Equipment and Safety
Pre mix each dye vat ingredient in small containers of water to avoid lumps. Always add powder to liquid, not liquid to powder (to prevent powder from flying everywhere). Wear gloves and an apron to avoid staining your hands and clothes. Always dye in a well ventilated area and use separate pots and utensils from your cooking pots.