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Mordanting Fabric for Natural Dyes

Preparing Fabrics for Natural Dyeing

SCOUR Meaning simply washing, but over a low heat to properly remove any oils and residue.

Soda Ash + Synthrapol for CELLULOSE ½ tsp per lb fabric (1 sq ft med wt)

Synthrapol for PROTEIN (or orvus soap)

*SYNTHRAPOL: Prewashing in Synthrapol helps remove oils, dirt, etc that can cause inconsistent dyes. Synthrapol as the after-wash keeps loose dye particles of dye in suspension so they don't stain other areas of the fabric. It is also pH neutral so it will not alter natural dye colors sensitive to pH change.


MORDANT Few natural dyes bond to your fiber on their own. Mordants are substances which are used to fix the dye to the textile. They also improve the brightness of color, but with some methods, will change the color. The term is derived from the Latin mordere, to bite. The most commonly used mordant is alum, and is considered a neutral mordant as it doesn’t change the color and often enhances. Other mordants are:

  • Iron (ferrous sulphate)
  • Tin (stannous chloride)
  • Chrome (bichromate of potash)
  • Copper sulphate
  • Tannic acid
  • Oxalic acid

SUBSTANTIVE dyes (lichens, walnuts, japanese maple, acorns)

Dye stuffs that are naturally high in tannins, do not need mordants, but definitely benefit when using both. They can also be used as mordants, but will affect your color as they all leave a tan to brown tone.

ADJECTIVE dyes need a mordant to bond with fibers.  The mordant enters the fiber, the dye follows and bonds

Metal Mordants (should not be inhaled!) Copper, Tin, Chrome have been used but used less and less as they are toxic.  If using these in your method use caution!  Masks, gloves, glasses, and proper ventilation should be used.  TIN; (harsh on wool, toxic)

Experiment; boil a tin can for at least one hour, and use the water bath as your mordant.


ALUM Recommended for protein fibers. Aluminum Sulfate has been used for years, will brighten colors, but not alter most,  and great will plant based dyes.  You can play using it as an after bath for some dyes changing the color as with cochineal.  It’s used in pickling and fertilizer.  It’s easy to get and safe.  Still use caution when boiling, making sure not to inhale fumes. 

To mordant the fabric (or fiber or yarn) simmer together with 1.75 tsp Alum and 1 tsp Cream of Tartar per pound of fabric for 1 hour. Allow the fabric to cool in the solution. Squeeze out excess water from material. Rinse in warm water.  Some leave in solution. You can allow the fabric to dry if you want to stockpile some pre-mordanted material, but you want to use it in about a month as over time the alum can degrade the fabric.



ALUMINUM ACETATE Buy or Make (Mix: 1 part calcium acetate or (sodium acetate) with 1 part Alum)

Recommended for cellulose fibers only. This will benefit from pretreating with a tannin dye stuff as well.

For this mordant you do not “cook” the fibre. For this reason a plastic container may be used for mordanting. 

Measurements per 1lb // 6Tbl (3 alum, 3 acetate) // Chalk 2Tbl OR Bran 5.6 Tbl = 1/3c

1) Measure aluminum acetate at 8% WOF, dissolve in hot water. Top up the kettle with enough hot tap water 38 - 50ºC (100 - 120 ºF) to fully cover the fibre when added. 

2) Add wet fibre (recommended to have been already mordanted with tannin). 

3) Let fibre sit for 1 - 2 hours stirring from time to time. Keep the bucket  covered and wrapped so that it retains its heat. 

4) Remove fibre and hang to dry

*Aluminum acetate must be fixed to the fibre prior to dyeing. In some cultures this is known as “dunging” as cow dung is used. Dung is high in phosphates, but you may also use wheat bran or calcium carbonate (our preferred choice).

5) Chalk* (fix) the fibre. Dissolve 50 g of chalk (calcium carbonate) in 5 litres of warm water. Dip fibre into this solution. Fully wet the fibre, wring out and proceed to dyeing. If using wheat bran, mix 100 g of wheat bran in 5 litres of warm water, fully wet the fibre, wring out and proceed to dyeing. 


IRON Ferrous Sulfate use as a mordant and also a color modifier.  You can buy the powder or create your own iron acetate.  Historically mud may have been used in dyeing as it’s high in iron.  Iron “saddens” colors so keep that in mind when choosing this method.  It can also make wool fiber brittle.  Using a softener after dyeing is advised.

  -Boil water in a stainless steel pot, add your “iron water,”  introduce wet fabric, simmer for 15 min. Allow to cool.  Strain and wring out fabric.  Never boil iron and inhale fumes!  

-To alter you dye bath colors, Always dissolve iron separately. Add a very small amount to bath, and then introduce fabric with either mordanting, dyeing, or modifying.

-Making an “Iron liquor or water” In the jar, place the rusty iron objects. Add 2 parts water to 1 part vinegar to the jar, filling the jar to cover the iron objects. Put the lid on the jar and seal tight. The water will turn to a rusty-orange color in 1 to 2 weeks. You can let your iron mordant liquor sit for as long as you like.  Add to it to keep it going, as you use from it. It’s hard to measure the amount of iron it holds, but I would say ½ tsp of powder may be equivalent to 1 Tbl of liquor.


SOY Greatly recommended for cellulose fibers.  You trick the fiber to reacting to the dye like a protein fiber.  Soy coated fiber should be used within two weeks. It further polymerizes becoming insoluble in water.   A half cup of dries soy beans goes a long way. You can make enough for 5 yds of fabric.

-Soak soybeans for about 8 hours.  Strain and rinse.

-Blend soaked beans in full blender of water for 4 minutes and strain and discard the liquid.

-Blend soybean pulp in blender of water again for 4 minutes strain and save the liquid. Discard the pulp. 

-Add water to your soymilk so it looks like skim milk. Store the milk in fridge for at the Most 3 days, but using as quickly as possible is necessary. 

-Soak your fiber for at least an hour.  I always soak overnight.  Wring out the soy lightly.  Lay fiber as flat as possible and store, and let it dry.  The trick is to not get streaks as it dries, which you can get if you hang it.  Some will paint on the fabric with a brush and dry flat. Sometimes I leave it in the fridge overnight and then let it dry.  A double dip is a great idea too. You must allow to dry between applications.

This process is really hard to time out and requires a lot of experimentation per fiber. Experiment! You should let the fabric sit for at least 3 days to work it's magic, but again, not longer than 2 weeks.

Symplocos pdf  from Maiwa for Bebali Foundation

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