Colourfast dyeing usually requires a mordant. Mordants are metallic salts that facilitate the bonding of the dyestuff to the fibre. Cellulose fibres also require a tannin in order to bond well. Tannins are not technically mordants (they are not metallic salts) but they are often included when speaking about the mordant process for cellulose fibres - as in, “mordanted with alum at 15% WOF and and myrobalan at 5% WOF.”

Some natural dye recipes still call for the use of heavy metal mordants such as chrome. Historically these were introduced during the industrial revolution and we do not recommend them. Heavy metal mordants can be toxic, presenting real challenges for safe use and disposal. Moreover most colours obtained through the use of heavy metals may be obtained through overdyeing or variations in the dye procedure. For those who wish to obtain a mordant from plants, Symplocos is a natural bio-accumulator of alum.

Mordant procedures for protein and cellulose fibres are not interchangeable.

Alum

Potassium Aluminum Sulfate

Potassium aluminum sulfate is the mordant most frequently used by dyers for protein (animal) and cellulose (plant) fibres and fabrics. It improves light and washfastness of all natural dyes and keeps colours clear. It is inexpensive and safe to use. This form of alum is refined from bauxite, the raw state of aluminum ore, and is free from the impurities (such as iron) some other alums may contain. Use at 15% WOF.


Aluminum Acetate
Aluminum acetate is often the preferred alum mordant for cellulose fibres and fabrics. It is refined from bauxite with acetic acid as a purifying agent. Some dyes develop to a richer shade on cellulose when mordanted with aluminum acetate. Aluminum acetate is the recommended mordant when printing with natural dyes. It is more expensive and sometimes hard to find. Use at 5-8% WOF.


Homemade Aluminum Acetate
Aluminum acetate can be made from sodium acetate and potassium aluminum sulfate. Depending on the availability of these materials in your area, this can be cost effective.

To make enough aluminum acetate to mordant 1 kilo of fabric, combine in 3 litres of hot tap water:

  • 150 g sodium acetate or calcium acetate

  • 150 g potassium aluminum sulfate

This can be added to your mordant bath (see the how-to section).

Aluminum Triformate
Aluminum Triformate is a gentle cold temperature mordant for natural dyes on cellulose and protein fibres. In the world of natural dyeing this is an exciting addition to the mordants available. At Maiwa, we have been testing aluminum triformate with all our dye, tannin, and fibre recipes for over two years. We have run all samples through rigorous light-fast and wash-fast testing and our conclusions are that this is an excellent mordant for wool and silk as it does not require heat in the mordant stage - and yet it creates a strong bond between the mordant dyes and the fibre.

For a cold temperature mordant for cellulose fibres this is an easy one step mordant procedure. However, we have found the lightfastness is less across many natural dyes. This is increased by doing a tannin process before the aluminum triformate process.

At Maiwa, for all our natural dyeing of cellulose, we still prefer to use our workhorse cellulose mordant process of tannin then alum and soda ash or aluminum acetate with or without tannin first. We are most excited about being able to use aluminum triformate on proteins without heat. Use at 5-8% WOF.