Before you start natural dying it is really important to understand mordants. What they do. How to use them. And safety issues.
Natural dyes are enhanced and made more permanent with the use of mordants. Mordants help set the dye pigment and improve the colour and light fastness. However due to growing awareness of the toxicity of some mordants, in particular chrome I only use alum which still gives me a wonderful range of colours and is the least harmful of all the mordants. Without a mordant the dye molecules simply lie on top of the fibre and will wash off.
Woad/indigo is exceptions to this, as they do not require a mordant; however the dyeing process is different and more complicated.
Mordanting can be done in two ways.
Mordants can be found in natural sources such stale urine and wood ash which give an alkali mordant. Acids are present in acid fruits or rhubarb leaves and are used today by only a small minority of natural dyers. These days it is more usual to use a chemical mordant such as alum which is available as a powder.
Alum is the easiest and safest mordant to use. Measure quantities carefully as too much alum leaves yarn or fibre feeling sticky.
Cream of tartar is not really a mordant, but is used to give luster and brightness to wool.
Unless you are intentionally aiming to influence the results of mordanting you should always use a stainless steel or unchipped enamel pot for your projects.
Other mordants which are used by some natural dyers are:-
Natural dyeing takes time and patience. Trying to rush the process or skip the mordanting process or being careless and not following instructions correctly will give you disappointing results. It is important to master your mordanting techniques if you are to produce consistent and professional results you will be proud of.
Natural dyes will only dye natural fibres. Natural fibres are grouped into two categories.
Vegetable (cellulose) which include, cotton, flax, jute, linen and hemp.
Protein (animal) which includes wool, alpaca, mohair, cashmere and silk.
Protein fibres are easier than vegetable fibres to use with natural dyes.
It is impossible to colour match when using natural dyes. Several factors will influence this. The plants you use may well have been grown in different soils. The weather conditions may have been different. The water may also be different. Also different fibres dye differently. Therefore if you require a certain quantity of yarn or fibre for a project, dye the entire batch together to ensure the colour is the same throughout.
Adding more than the recommended quantity of mordant does not mean you will get a better result. In fact it means the opposite! It weakens the fibre and makes it brittle – it can even make it slimy.