How to Mordant Plant Fibers

Our How To guides are intended to make the dye process easy, from How To Mordant to scouring your fibers to dyeing with an assortment of dyes. You can find other How To guides here.

WHAT IS MORDANTING?

Mordanting is the most important process of preparing fibers to accept color. This is not an optional step but there are many mordant variations, and indigo as a vat dye does not require a mordant. Using a mordant helps to ensure the most durable and long-lasting colors.

(Check out our recent Q & A: Round Up of Mordanting + Scouring 101 here.)

All mordants are calculated based off of a percentage of the weight of fiber or WOF. Weight of fiber (WOF) refers to the dry weight of the yarn or fabric to be mordanted. It is used primarily when weighing mordants and dyes and allows you to quickly and easily calculate how much to measure. Therefore, a kitchen scale is handy to determine the weight of yarns or fabrics. We have also provided easy teaspoon and tablespoon measurements based off of 100 grams of fiber.

MORDANTING PLANT FIBERS

We prefer mordanting plant-based cellulose fibers with aluminum acetate, and then following with a wheat bran or a calcium carbonate bath, and either of these ingredients help to improve the aluminum acetate's performance. This particular method is adapted from an email conversation with Michael Garcia.

Don't have aluminum acetate? You may also successfully mordant using tannin and aluminum sulfate. This is a traditional mordant used for plant fibers prior to the introduction of aluminum acetate and is applied room temperature. Instructions are available here and are courtesy of Catharine Ellis and Joy Boutrup's book, The Art and Science of Natural Dyes.

Once you are comfortable with these techniques, you may explore other mordant options, including the use of iron, or tannin alone and compare results.

SAFETY INSTRUCTIONS

We recommend wearing a dust mask or respirator, gloves, and an apron with all powders as they can be irritating to the nose, throat, and skin. Aluminum acetate is very powdery, smells strongly of vinegar and can irritate nose and throat. We strongly recommend adult supervision if working with children. 

We also recommend that you keep dye tools and utensils separate from kitchen tools and work with plenty of ventilation. Alum may be safely disposed in a municipal water system by pouring down the drain. Do not dispose of in waterways or drains that flow into waterways.

CALCULATING THE AMOUNT OF MORDANT

Aluminum acetate: the recommended amount of aluminum acetate is 5 to 10% WOF, or 2-4 rounded teaspoons for 100 grams of fiber. The higher percentage of mordant will increase the depth of shade.

Wheat bran: the recommended amount of wheat bran is 5% WOF, or 4 teaspoons for 100 grams of fiber.

- OR -

Calcium carbonate: the recommended amount of calcium carbonate is 5% WOF, or 1 rounded teaspoon for 100 grams of fiber.

WHAT YOU WILL NEED:

This list of ingredients is for 100 grams/4 ounces of fiber, and with 5% aluminum acetate. Adjust the amount of materials as necessary, per the percentage guidelines above. Note that if you use hot tap water, you will not need to heat the mordant bath.

For mordanting:

  • 100 grams/4 ounces cellulose fiber
  • 5 grams/.17 ounces/2 rounded teaspoons of aluminum acetate
  • A container to dissolve the aluminum acetate
  • Heat source (optional; see Note above)
  • A large stainless steel dye pot
  • Dye rings (if dyeing skeins)

Choose either wheat bran or calcium carbonate as your final bath. You do not need to do both.

For wheat bran bath:

  • The above 100 grams/4 ounces of mordanted fiber
  • 5 grams/.17 ounces./4 teaspoons wheat bran
  • Cheesecloth

For calcium carbonate bath:

  • The above 100 grams/4 ounces of mordanted fiber
  • 5 grams/.17 ounces./1 rounded teaspoon calcium carbonate

Primary Instructions:

Wet out the aluminum acetate in cold water and dissolve in boiling water. It may be a bit lumpy and sticky, but the lumps work out fairly quickly. A whisk is helpful. We recommend a dust mask when dissolving aluminum acetate as it is very powdery and the strong vinegar smell can be irritating.

Fill a dye pot with hot water from the tap – approximately 110-120°F. If you use hot tap water, you do not need a heat source as this is sufficient heat for mordanting. You may also use a clean bucket or container for mordanting with aluminum acetate.

Add the dissolved aluminum acetate and stir well. Then add the fiber to the dye pot, rotating the fibers gently. Press out air bubbles under fabric folds, or in floating yarn.

If you are heating cold water, heat only to 110°F.

Rotate goods occasionally and hold for 45 minutes.

Remove fibers from the dye pot. Rinsing is not necessary. Remove excess water and proceed to the wheat bran or the calcium carbonate bath.

Wheat bran bath

Enclose the wheat bran in a cheesecloth bundle if you don’t want bran bits all over your fibers. Soak the wheat bran bundle in a small bucket or container of water just off the boil for about 30 minutes. The solution will be milky. This solution lasts about 1-3 days. If you notice it starting to bubble or smell fermented, it's time to make a fresh solution.

Fill a bucket with hot water from the tap – approximately 110-120°F that is large enough to hold your mordanted fabric. If you use hot tap water, you do not need a heat source as this is sufficient heat for the bran bath. Add the bran solution and the bundle of bran to the bucket. You can gently squeeze the bran bundle to extract more of the bran goodness.

Place the mordanted fibers into the bath for 30 minutes, rotating occasionally.
Remove the fibers from the bath. Do not rinse before placing into the dye bath. The fibers are now ready for dyeing.

Calcium carbonate bath

Mix the calcium carbonate with boiling hot water and add to a bucket or container large enough to hold your goods. Add yarn or fiber and leave for 15-30 minutes. Remove, rinse lightly and proceed to dyeing. Calcium carbonate can shift dye colors due to its higher pH, so we like to rinse it prior to use.

Reusing the bath to save water and mordant

You may leave the fibers in the mordant solution overnight, then extract excess water and proceed to dyeing. Some dyers feel this increases the depth of shade of the finished piece. You may store damp mordanted fibers in a plastic bag and refrigerate up to 7 days, and cure or age, as this also seems to increase the depth of shade in the dyed fibers. You may also dry and store mordanted fibers for future use; we recommend using cellulose mordanted fibers within 6 months of mordanting. Label and store your mordanted fiber and keep it away from dust or dye powders, as it is vulnerable to staining.

Reuse aluminum acetate baths at least twice. If you observe cloudiness or flakes floating in the bath, it is time to change it. Recharge the bath with 50% of the amount of required mordant, or 1 teaspoon per 100grams of fiber for a 5% solution, or 2 teaspoons for a 10% solution.