We've divided the section on Mordants into three parts. We start with some explanations and then describe different mordants, tannins, and other additives. We will give detailed procedures in part three. What follows depends on knowing what fibre you are working with. You may wish to review fibres before reading on.

There are only a few dyes(1) (such as indigo) that can effectively be put on a fibre without first mordanting.

Mordanting the fibre is perhaps the most important step in successful dyeing. It is often rushed or even omitted because no visible change occurs. When we teach natural dyes, we notice that if students can grasp the necessity of good mordanting before they embrace the excitement of colours, then they are well on their way to successful and satisfying results.

Advanced dyers will use the mordanting step itself as a means to influence colour. Mordants can be added through blockprinting or silkscreening techniques, or the application can be controlled through resist techniques. This gives a variety of methods to add pattern to a cloth. Some very subtle effects may be created through control of mordants and tannins.

Mordanted yarns - almost indistinguishable from unmordanted yarns.

Mordants facilitate the bonding of the dyestuff to the fibre.There are many mordants and each one will encourage a different shade from a particular dyestuff. As mentioned earlier we do not recommend mordants such as chrome, copper and tin. Although these metallic salts work well to fix the dyes and provide an alternate palette, they are a health hazard and produce toxic waste which requires special disposal. Mordants such as alum, iron, and tannin are safer to use and can produce myriad colours when used in conjunction with the appropriate natural dye. The most frequently used method is premordanting (before dyeing). Occasionally the mordant is added to the dyebath (one-pot dyeing) and sometimes it is added after the dyebath (postmordanting or after-mordanting). Mordant procedures for protein and cellulose fibres are not interchangeable.




mordants

Alum – 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 (see our safety notes). 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 can contain.

 Use at 12-20% WOF. Sometimes we use a combination of two mordants of alum. For example, we will mordant once with alum at 15% WOF and then again with a fresh mordant bath of alum at 15% WOF. Or we will do a tannin/alum/alum mordant to achieve slightly richer colours.

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Alum Acetate – Aluminum acetate is sometimes used as the preferred alum mordant for cellulose fibres and fabrics. It is refined from bauxite and acetic acid is used as a purifying agent. For this reason some natural dyes develop to a richer shade on cellulose. Alum acetate is the recommended mordant for printing with natural dyes. It is more expensive and sometimes hard to find.

Use at 5-8% WOF

Homemade Alum Acetate – The dyer may make aluminum acetate from sodium acetate and potassium aluminum sulfate and, 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:

1 Dyes which do not require mordants are sometimes referred to as substantive dyes. Indigo is the best example of a substantive dye. Occasionally the term substantive will be used for dyes like walnut and myrobalan which are are also tannins. For the natural dyer who wishes the greatest flexibility we recommend that fibres always be properly mordanted.

The Maiwa Guide to Natural Dyes

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