Iron mordant is used to colour protein fibres (wool, hair and silks) with natural dyes.
Please note: the ferrous sulphate now available is from a different source and it has a higher level of insoluble impurities, mainly fine sand. You are therefore advised to dissolve the chemical in water (200gm of ferrous sulphate/litre) before use, allow the insoluble material to settle, then pour off the liquid for use. Remember to weigh the chemical before dissolving and measure out the water. Use an appropriate quantity of the solution to give the weight of solid ferrous sulphate necessary for your work.
Iron mordant links chemically with the fibre and creates attachment points which bond with the colourant from natural dyes creating light and wash fast colours. It alters the colour obtained from dye plants (depending on the plant used) darkening the colour, known as ‘saddening’, yellows towards orange, reds to brown and purples to black. We encourage experimentation and recommend careful record keeping to help reproduce colours in future dye sessions.
It helps to soak the wool in warm water and squeeze out excess before adding to the mordant bath. For every 250g of the dry wool or silk, use 5-10g of ferrous sulphate in 5 litres of water. Gradually heat the mordant bath to around 80°C for 30 minutes and allow to cool slowly. Remove the wool and squeeze to remove excess liquor.
After mordanting, the wool can be simmered with any of the natural dyes. It may help to place the dyestuff in a mesh bag before adding to the dyebath. Simmer for approximately 30 minutes and turn off the heat. Allow the wool to cool slowly in the dyebath before removing it. Gently rinse out excess dye in clean water.
Alternatively fibres which have been dyed using alum, copper, tin or chrome mordants can be saddened by soaking in a warm bath using the same quantities of fibre, to water and iron mordants.
Iron mordant has also become popular for use in Botanical Printing, also known as ECO printing. This experimental technique is effective on cotton and linen fabrics, as well as wool fabrics including felt, silk fabric and cotton paper. The material is first soaked in a solution of alum mordant (or alum and iron solution) and leaves and petals are placed onto it while it is still damp. The fabric is folded, rolled up and parcelled in cling film or aluminium foil before being steamed to extract the colour. Likewise, leaves and petals can be sandwiched between sheets of mordanted paper and steamed. See here for our steaming instructions which are used to heat-set silk dyes.
Iron will begin to oxidise when it comes into contact with air, this alters the colour from green to rusty brown. This change of colour does not affect the performance of iron as a mordant.
There are hazards associated with the use of this product. Follow the advice on the label at all times.