Mordants are important when dyeing with natural dyestuffs. Their purpose is to fix the dye to the fabric so it is wash and light fast. Mordants can also be used to change the colour of the dye.
Eucalyptus leaves contain natural mordanting properties, so additives aren’t needed to fix the dye to the fabric as long as it is a protein fibre such as wool or silk. Various natural mordants can be used to fix Eucalyptus dyes to plant fibres such as cotton, linen or hemp, and some are mentioned in the recommended books. I use soda ash as it works well with fibre reactive dyes on plant fibres.
In my experience to date, eucalyptus bark does not contain a mordant so can be dyed with leaves to fix the colour.
Different colours can be achieved when using different varieties of leaves, and the colour is as variable as the region or location of the tree, so the results are as unique as your tree. For example, we have many introduced Red Ironbark (Eucalyptus sideroxylon) in our neighbourhood. Some of the trees, particularly the ones planted on the roadside, don’t yield much colour at all. Others, planted in reserves or parks, give a good apricot to rust or shades of lime to deep olive-green depending on the mordants used.
As much as possible, I like to use containers and not additives to the dye to change the colours. Some additives are toxic and I only use the safer alum or potassium aluminium sulfate and vinegar. The containers can be neutral such as enamel or stainless steel, or can alter the natural dye colour of the leaves such as tin, copper or cast iron.
Simmer dyeing is discussed in the next article.