alum-tannin mordant
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Mordant Cotton with the 3-step alum & tannin process

This is a traditional process that has been thoroughly tested for many years. It also allows you to use tannin bearing plants like sumac leaves instead of tannic acid. If you want areas of pure white, tie or mask the area before mordanting as the tannin gives the fibres a pale yellow tinge. Buy alum and gallnut extract/tannic acid here.

Total weights to mordant 100 grams of fibre:-

  • Alum: 50 grams (25 grams in each of Baths 1 & 3)
  • Soda Ash: 12 grams (6 grams in each of Baths 1 & 3)
  • Tannic Acid: 6 grams of tannic acid or Gallnut Extract (for Bath 2 only).

Pre-wet 100 grams of cotton fibres in warm water for at least two hours.

  1. Bath 1: Fill half of dye pot with water. Bring nearly to boil. Dissolve 25 grams of alum in a small container with boiling water. Slowly add alum to pot and stir well. Weigh out 6 grams of soda ash but do NOT add water to the soda ash! Soda ash causes the water to bubble vigorously. Instead add the soda ash slowly and carefully to the water in the pot. When the bubbles have subsided add more hot water to the pot. Add pre-wetted fibres, heat to simmering point and simmer for an hour. Stir the fabric every fifteen minutes and then leave the fibres in the pot for 24 hours. It is not a problem to leave fibre in the pot at any of the stages for a few days. Wring well and dry. Leave the fibre to age for at least a week. When you are ready for the next step, wash the fibre well.
  2. Bath 2: (Tannin): Fill pot 2/3 with hot water. Dissolve 6 grams of tannic acid in a small container with boiling water, (otherwise particles may stick to bottom of saucepan). Add tannic acid to pot and dissolve well. Add pre-wetted cotton and then simmer for one hour. Leave for 24 hours and wring well and dry. Leave the fibre to age for at least a week. When you are ready for the next step, wash the fibre well.
  3. Bath 3: (Second Alum Bath): repeat the alum mordanting as described for Bath 1.

Dark colours: To get dark colours dye the fibres, wash the fibres, re-mordant with alum and soda ash and dye again. For really dark colours re-mordant using the three step process.

Go to
How to scour cotton

How to mordant cotton

Mordanting with aluminium acetate

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Updated on 19 April 2021
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