Alum acetate advanced
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How to Mordant Cotton with aluminium lactate/acetate

b) Mordanting cotton with aluminium lactate or acetate: advanced method (2 step)

This method yields better colours than using aluminium lactate or aluminium acetate alone but it requires pre-treatment with tannin which increases the light fastness of the dye.

Aluminium lactate is a new mordant, which is used in the same way as aluminium acetate. This product is manufactured from lactic acid from sustainable sources. It is made from by-products of the sugar industry, maize or starch derivatives. It dissolves better than aluminium acetate.


You will need;
  • 10 grams of gallnut extract (or source of tannin)
  • 10 grams of aluminium lactate or aluminium acetate
  • 100 grams of scoured cotton fabric or yarn

Step 1: Tannin treatment

  1. Soak 100 grams of cotton fibres in warm water for at least two hours.
  2. Half fill the dye pot with hot tap water
  3. Dissolve the gallnut extract in a small container with boiling water.
  4. Add the dissolved gallnut extract to the dye pot and stir.
  5. Add the wet cotton to the pot.
  6. Wearing rubber gloves check, that the water is not too hot for your hands, work the tannin well into the fabric or yarn for a few minutes, squeezing the fabric and then unfolding it a few times. If you are mordanting yarn, especially fine weaving yarn, work the fibre in the pot very carefully, otherwise the yarn will become tangled. Let the fabric or yarn sink to the bottom of the saucepan. Add a bit more hot water if there is space in the saucepan, but don’t fill to the very top.
  7. Leave the cotton in the pot for a couple of hours or overnight.

Step 2: Aluminium lactate or acetate

  1. Half fill the dye pot with hot tap water
  2. Dissolve the aluminium lactate or aluminium acetate in a small container with boiling water.
  3. Add the dissolved aluminium lactate or aluminium acetate to the dye pot and stir. There is no need for extra heat as the warmth from the hot tap water should be enough.
  4. Add the wet cotton (that has been treated with tannin) to the pot and wearing gloves, work the fabric or yarn inside the pot as you did with the tannin. Leave overnight. Wring well and dry. If you are using aluminium acetate, Liles recommends waiting until the vinegar smell has disappeared, which he says can take up to 4 days.
  5. When you are ready to dye, rinse the fibre carefully to remove any unattached mordant.

Go to:

How to scour cotton

Mordanting cotton with aluminium lactate/acetate: basic 1-step method

Mordanting with the traditional 3-step alum-tannin process

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Updated on 19 April 2021
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