Mordants for natural dyes
“Step by step one goes very far”
Definition of mordant: Biting and caustic in thought, manner, or style. The word derives from the french word mordre which means to bite. When mordanting fabric for natural dyeing, a better way to describe the process is "a metallic salt that combines with a natural dye to form a pigment" (reference Maiwa).
Mordants are another key process to getting the best results from your fabric and dye. And yes this is another step where you won’t see any colour change on your fabric. A good understanding of the mordants and the process will give you the fullest potential from your dye and a wider range of surface pattern techniques.
Mordants are the key to getting lasting colours.
Not all colours are fully formed in the plant and in a lot of dyes, it is not a case of just getting the colour you see from the plant onto a piece of cloth. Natural dyes just don't work this way, it is more about a process of metamorphosis, in which you need fibre, a natural dye, and a mordant (unless using Indigo).
The dye is from organic matter (something living)- a plant/animal.
The mordant is from something inorganic (not living) - a metallic salt.
Both the organic and inorganic elements need to interact with each other to make a permanent colour. This interaction is more than just sticking colour onto fabric, the mordant is not like glue.
Mordants are metal salts which are dissolved in water. Natural dyes also start as soluble, however, when you combine the two you get an insoluble pigment, which is insoluble and therefore does not dissolve in water at all. The key is getting this reaction to happen on the fabric itself. Thus creating a dye that will stay permanently on the fabric and not wash off.
Some mordants are clear like Alum, and some have a colour like Iron and Copper.
For protein fibres - Silk, Wool and Leather I like to use Potassium Alum Sulfate (Alum).
Potassium Aluminum Sulfate is a safe mordant and one that is frequently used by natural dyers for protein (animal) fibres. However, it can also be used for cellulose (plant) fibres and fabrics. It helps improve the light-fastness and wash-fastness of natural dyes and helps keep clear colours. Potassium Aluminum Sulfate is commonly used in water purification, leather tanning, and baking powder as the E number E522. It also has cosmetic uses as a deodorant and as an aftershave treatment. It has been used as far back as the Early Egyptians around 1500 BC. More history on Potassium Aluminum Sulfate - HERE.
Make sure when buying it is pure Potassium Aluminum Sulfate, other substitutes won’t be as effective for mordanting.
For cellulose fibres - cotton, linen, hemp and bamboo I like to use Tannin with Aluminum Acetate.
Tannin is used alongside the mordant of cellulose fibres. Aluminum Acetate or Alum does not bond very well with cellulose fibres. Tannin does bond well with cellulose fibres and so once the fabric is treated with tannin, the alum will combine with the tannin/fibre complex. Some natural dyes contain tannin and may not need the tannin step of the mordant process (Oak, oak galls, pomegranate, cutch, etc).
Tannins can be clear or they can add colour to the fibre, this is an important consideration when selecting which tannin to use. Experiment with different tannins and find the one that works best for the colours you like. Different tannins require different % per WOF.
Aluminum Acetate is my preferred alum mordant for my cellulose fabrics. I find that it can give cleaner and richer results. I also find it gives better results when used for fabric that is printed or eco printed onto.
