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Mordant Wool and Silk

When you have decided which mordant you wish to use – (in my case as previously stated it is always alum) proceed as follows:

  • Calculate 10% alum (aluminium potassium sulphate) to the weight of the dry fibre and 5% cream of tartar to the weight of fibre.
  • Cream of tartar is not a mordant; it is an assistant that allows more alum to be absorbed by the fleece. It also modifies the final colour when using madder or cochineal.
  • For example: for every 100g of dry, scoured fibre to be mordanted carefully weigh 10g of alum in a heat resistant bowl and 5g of cream of tartar in another heat resistant bowl.
  • After weighing the dry fibre soak it in water for several hours as this opens up the fibres making the whole process of mordanting and dyeing easier. The fleece/fibre is also less likely to float to the surface of the bucket.

After soaking continue as follows –

  • ¾ fill a stainless steel bucket with cold water.
  • Dissolve the alum with very hot water and add to the bucket of cold water and stir well.
  • Dissolve the cream of tartar with very hot water and add that to the bucket of cold water and stir again. After soaking the fibre, add it to the bucket and slowly bring it to a simmer, (do not exceed 80 degrees C) Ensure all the fibre is submerged but do not agitate as this will cause wool to felt.
  • Simmer for 1 hour; turn off the heat source and leave to cool in the bucket overnight. (24 -48 hours give better results)  Remove the fleece/fibre from the bucket.
  • You can now rinse the fleece/fibre and use it for dyeing immediately, or dry it without rinsing, to be used at a later date; however, if you dry it, it must be rinsed and soaked well before dyeing.


The same mordant can be used for silk and wool –  however, silk requires even more care as it can lose its natural sheen by overheating – the golden rule being -keep the temperature to just below simmering.

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