A mordant is required if the colour from natural dyes is to remain wash fast. Materials can be pre-soaked in a mordant and left damp prior to dyeing. The mordants can also be added to the dye bath while the dye is being simmered. Mordanting materials before and after dyeing with natural dyes will add extra fastness.
Dyeing without Chemicals
The quantities of mordant used in preparing fibre for dyeing have been the subject of much disagreement over recent years. Historically the craft dyer used 'enough' to make sure the job was done well. This gave rise in recent years to a strong reaction for ecologically sound mordanting where the levels of mordant were reduced considerably, alternative mordants were sought out, and additives used to increase the effectiveness of mordants. The most extreme version was the concept of 'dyeing without chemicals'. The belief that oxalic acid used as a mordant and derived directly from rhubarb leaves and roots is 'good' and the same substance from a factory is 'bad', is prejudiced. Oxalic Acid is a listed poison!
The common mordants are Alum (Potassium Aluminium Sulphate), Copper (Copper Sulphate), Tin (Stannous Chloride), Iron (Ferrous Sulphate) and Tannic Acid. These are used in various combinations with assistants for mordanting wool, cotton, linen and silk.
Before dyeing, it is important to check whether the item is 'Prepared for Dyeing' (PFD) or requires scouring to remove any grease, oil or starch. Run a few droplets of cold water onto the fabric. If they soak in quickly, no scour is necessary. To remove starches, size and oils, add 5ml of Synthrapol (a non-ionic detergent) along with 2-3 litres of water for each 100g of material. Stir gently over a 15 min period, and then rinse thoroughly in warm water. It is possible to use household detergent, but the alkaline residue may affect the final colour or wash fastness.
Mordants for Dyeing Wool and Silk (Protein) Fibres
The quantities of mordants shown are for 500g of dry weight of woollen fibres with five litres of water. Bring the mixture to boiling temperature and hold there for one hour. Do not agitate as this will felt the fibres. Allow to cool, rinse and dry.
- Alum Mordant: 100g, it helps to add 35g of Cream of Tartar (Potassium Hydrogen Tartrate). Use of more than 150g of Alum will tend to make the fibre feel sticky.
- Copper Mordant: 100g, add 20g of Cream of Tartar to improve colour and light fastness.
- Tin Mordant (Stannous Chloride): Use with natural dyes to brighten colours, especially yellows, oranges and reds. Do not use too much Tin as this will make the fibre brittle
- Iron Mordant: 20g in solution is added to the dye bath after dyeing to darken the dye colour
Experimenting and careful note taking will help you to repeat the colours and results achieved by these mordants.
Cotton and Linen (Cellulose) Fibres
Cotton and Linen dyeing requires a different approach. The metallic part of the mordant does not attach readily to cellulose until it has reacted with Tannic Acid (tannin). First dissolve 40g of Tannic Acid in 5 litres of hot water. Steep the fibres in the bath for up to 24 hours.
To mordant the prepared fibres mix 250g of Alum and 25g of soda ash (anhydrous sodium carbonate) in 5 litres of hot water and allow to soak for up to 24 hours, rinse in warm water and dry and then repeat the mordanting. Copper and Tin mordants can be used in similar proportions as for wool to assist with blues, blacks and reds.
Alternatively, Aluminium Acetate acts as an effective mordant for Cotton (and other cellulose fibres) when using natural dyes, giving a significant difference in colour take-up and improved light fastness. Use the Aluminium Acetate as a 5% solution for best results - this article, from Turkey Red Journal (opens in a new window), confirms usage.