Its time to get to grips with Mordants

According to Jenny Dean, a mordant is a substance that has an affinity with both the fibre that is to be dyed and the natural plant dyestuff that has been chosen to colour the fibre. It therefore acts as a bond between fibre and dyestuff, so that the dye is driven permanently into the fibre. Even though many plants stain fibres when used without a mordant, the addition of a mordant will yield a stronger, more intense and more permanent, lightfast and wash-fast colour on the fibres.

Some plant dyes that contains a lot of tannin (such as indigo and woad) will fix onto the fibre without the need for a mordant. Other plants (such as oak galls, rhubarb leaves or the leaves of stagshorn sumach) contain natural mordants, and purists may choose to use them to fix natural dyestuffs. However, most dyers use chemical mordants, as these can be weighed more reliably. 

The most common chemical mordants used by dyers are compounds of aluminium (alum), copper and iron, though as iron dulls, darkens or ‘saddens’ naturally dyed colours (I just love the idea of a colour being saddened!) it is more often used as an ‘assistant’ or ‘modifier’ (that is, as a supplementary chemical during or after dyeing) than as an actual mordant. Chrome and tin can also be used as mordants. All mordants, including those derived naturally from plants, are poisonous to some degree, so they should be used and disposed of responsibly.

Different mordants yield different colours when combined with the same dyestuff. If three skeins of the same wool are mordanted with alum, copper and iron respectively, and placed in the same dye bath, three different colours will be obtained. I’m planning to explore this later on in my project.

Jenny Dean says that, although it is technically possible to mordant and dye fibres simultaneously in one combined process, to be most effective the fibres should be mordanted in a separate process to the actual dyeing. This is known as pre-mordanting. Once they have been pre-mordanted, the fibres can be dried, labelled and stored indefinitely for future use. I’m planning to pre-mordant my skeins of wool in batches of ten: five with alum and five with copper. 

I’ve set down the recipes for my alum and copper mordants as follows:

Recipe for Alum Mordant

Sufficient to mordant 5 x 20 gram skeins (i.e 100 grams, dry weight) of wool. The wool should be wetted thoroughly before it is mordanted so that the mordant will take evenly.

• 8 grams of alum dissolved in a small amount of boiling water in a jug

• 7 grams cream of tartar dissolved in a small amount of boiling water in a jug

• 100 grams (dry weight) of wool, already prepared to receive a mordant by having been tied loosely into a skein and washed in warm water containing a few drops of wool-friendly detergent to remove any dirt, grease or chemical residue from industrial processing

• 4 litres of cool water in a stock pot

Add first the dissolved cream of tartar and then the dissolved alum to the mordant bath and stir. Add the wetted wool and bring the bath up to simmering point. Simmer for one hour, agitating gently from time to time. Switch off the heat and leave the bath to cool overnight. Remove the skeins of wool from the cool mordant bath, rinse them and hang them up to dry or use them immediately in a dye bath.

Recipe for Copper Mordant

Sufficient to mordant 5 x 20 gram skeins (i.e 100 grams, dry weight) of wool. The wool should be wetted thoroughly before it is mordanted so that the mordant will take evenly.

• 2 grams of copper sulphate dissolved in boiling water in a jug

• 40 millilitres of vinegar

• 100 grams (dry weight) of wool, already prepared to receive a mordant by having been tied loosely into a skein and washed in warm water containing a few drops of wool-friendly detergent to remove any dirt, grease or chemical residue from industrial processing

• 4 litres of cool water in a stock pot

Add the coper sulphate solution and then the vinegar to the mordant bath. Stir well. Add the wetted wool and bring the bath up to simmering point. Simmer for one hour, agitating gently from time to time. By this point, the wool should be pale green and the water virtually clear. Switch off the heat and leave the skeins of wool to cool overnight. Remove the skeins, rinse them and either hang them to dry or use them in a dye bath at once.

If you try this, the first thing that may strike you is the small quantity of each chemical needed. I was so surprised that I felt I had to check my figures. I have bought enough alum to dye 312 x 20 gram skeins of wool, and enough copper to dye 1250 x 20 gram skeins of wool! I don’t think I’ll be running out of mordants for some considerable time. However, I could get through a lot of skeins of wool over the course of the year. 

To illustrate this point, the Winterbourne Dyers put eight skeins into each dye bath that they made up! Seven of these had been pre-mordanted with alum and one with copper. The first skein recorded their ‘standard’ colour, the second was tested for lightfastness, the third and fourth were over-dyed with woad and madder, the fifth was ‘modified’ with dilute distilled vinegar, the sixth with washing soda and the seventh with iron. The eighth was the copper mordanted skein. I’m fairly sure they were following Jenny Dean’s advice on modifying dye colours, as in ‘Wild Colour’ she suggests leaving one skein per dye bath unmodified as a standard shade, when playing with acid, alkaline, copper and iron modifiers to extend the range of colour from a dye bath. 

Jenny Dean’s standard colour swatches for each dye plant she recommends in ‘Wild Colour’ show what might be expected from the dye applied to an un-mordanted fibre, a fibre treated with an alum mordant, an un-mordanted colour with iron used as a ‘modifier’ after dyeing and a fibre that has been treated with both an alum mordant before dyeing and and an iron modifier after dyeing. 

I don’t think (at least, at this early stage in my project) that I shall be so ambitious, as I would soon accumulate many, many coloured skeins of wool. Right now, I’m thinking of dyeing just two skeins of wool per dye bath, one pre-mordanted with alum and the other with copper. 

Some plants are reported to yield bright colours when pre-mordanted with tin, so I may try this as a mordant at a later stage in my project, if it seems like a good idea. I may also make a separate experiment in the use of modifiers on one specific dye plant, where this would extend the range of colours that i could obtain in an interesting way. I’ll report on these ideas as I try them out.