How to Mordant

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

WHAT IS MORDANTING?

Many natural dyes require the use of a mordant to achieve the most durable and long lasting colors. Mordanting prepares the fibers to bond with natural dyes and is typically a separate immersion bath for the fibers. The technique is simple:  measure the mordant, dissolve in water, and add to a dye pot or bucket or tub filled with water.  Add the fibers and hold them for a period of time, then remove and proceed to the dye bath. Although many substances have been used in the past for mordanting, we prefer aluminum potassium sulfate as a mordant for protein (wool) and aluminum acetate for cellulose (cotton, linen, bamboo, etc.) fibers, as well as for protein/cellulose blends, like wool/hemp, silk/bamboo and silk/cotton. If you are dyeing cellulose fibers, please scroll further down to the Mordanting Cellulose Fibers section.

All mordants are calculated based off of a percentage of the weight of fiber. “Weight of fiber” 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. 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.

Which mordant to use?

For basic mordanting, refer to this table.  Once you are comfortable with these techniques, you may explore other mordant options, including the use of iron, tannin and alum, tannin alone and compare results.

Fiber content Recommended Mordant Other Mordant Options
Wool, Alpaca Aluminum Sulfate with optional Cream of Tartar
Silk Aluminum Sulfate Aluminum Acetate with wheat bran afterbath
Cotton, Linen, Tencel, Bamboo and other plant fibers Aluminum Acetate with wheat bran afterbath

 

MORDANTING WOOL

Aluminum sulfate is a metallic salt derived from bauxite, a mixture of minerals.  The historic alum mines were located in Southern Europe (France and Italy), and in Greece and Egypt. Control of alum veins gave nations great power as the mineral was prized for its ability to create deep, bright shades for textile dyeing. Present day reserves of bauxite are found in Australia, Canada, Brazil, and Africa and these regions are the largest exporters of alum.  In the US, Alabama, Georgia and Arkansas held alum mines but their current output is negligible.

Mordanting provides the dyer flexibility as fibers can be mordanted in advance, dried, and dyed later, or mordanted and dyed in one day. Drying and storing, or “curing” alum-mordanted fibers often results in deeper shades on wool and silk. If you are new to natural dyeing, we recommend starting with wool fiber as it is the easiest to dye.

Cream of tartar can also be used as an adjunct to mordanting wool  Its purpose is to assist the alum to bond with the wool and it also keeps wool fibers soft.  Bear in mind that it will shift colors, and in some cases, can inhibit the development of certain shades.

CALCULATING THE AMOUNT OF MORDANT

Aluminum sulfate: the recommended amount of aluminum sulfate is 12% of the weight of fiber, or 1 scant Tablespoon for 100 grams of fiber. Note that you can go up to 20% of the fiber weight, or 1 Tablespoon + 1 teaspoon per 100 grams of fiber. More mordant results in deeper shades with many of the colors, especially the red dyes.

Cream of tartar: the amount of cream of tarter should be 6% of the weight of fiber, or 1 1/4 teaspoons for 100 grams of fiber. You can use aluminum sulfate and cream of tartar together, the cream of tartar brightens many colors and helps keep wool fibers soft.

SAFETY INSTRUCTIONS

We advise 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 sulfate is considered non-toxic but still should be handled with care as it is astringent and drying to skin. If working with children, adult supervision is strongly recommended.

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.

WHAT YOU WILL NEED:

This list of ingredients is for 100 grams/4 ounces of fiber, and with 20% aluminum sulfate for a deeper shade. Adjust the amount of materials as necessary, per the percentage guidelines above.

  • 100 grams/4 ounces fiber
  • 20 grams/.8 ounces/1 rounded Tablespoon + 1 teaspoon of aluminum sulfate
  • A container to dissolve the aluminum sulfate
  • A large stainless steel dye pot
  • Heat source
  • Optional: 6 grams/.25 ounces/1 1/4 teaspoons cream of tartar
  • Dye rings (if dyeing skeins)

Instructions:

Measure the aluminum sulfate and pour it into a container that you can pour hot water into and mix it. Bring about a cup of water to a boil, and pour it into the container to dissolve the aluminum sulfate. If using Cream of Tartar, dissolve separately.

Fill a dye pot with room temperature water, and place on a heat source, then add the dissolved aluminum sulfate and cream of tartar to the pot and stir well.

Add the fiber to the pot, rotating the fibers gently. Make sure there are no bubbles under fabric folds, or that any yarn is floating. Slowly bring the temperature up to 180°F and hold for 45 minutes. Rotate the fibers occasionally and gently.

Allow to cool briefly, and then remove fibers from the dye pot.

Rinse in similar temperature water, remove excess water from the fibers, and proceed to dyeing.

Notes:

Many dyers will reuse their alum bath for multiple mordant sessions to save water and mordant. Aluminum sulfate baths may be reused at least twice and one customer reuses her alum bath up to 7 times! To recharge the bath, add about 25% additional dissolved alum, or 1 additional teaspoon per 100 grams of fiber, stir and mordant as above. If you observe excessive cloudiness or large flakes floating in the bath, it is time to change it.

You may leave the fibers in the mordant solution overnight to cool, then remove excess water. Some dyers feel this increases the depth of shade in the finished piece.

Mordanted fibers may be stored damp in a plastic bag and refrigerated for 3-5 days and cured or aged, as this also seems to increase the depth of shade in the dyed fibers.  Curing normally produces a deeper color, but be aware that fibers mordanted with alum and cream of tartar can get moldy if they are stored longer than a week while damp.  Finally, mordanted fibers may be air dried and stored for future use. Label and store your mordanted fiber and keep it away from dust or dye powders, as it is vulnerable to staining.

MORDANTING CELLULOSE FIBERS

We prefer mordanting our cellulose fibers with aluminum acetate, and then following with a wheat bran bath, helping to improve the aluminum acetate’s performance. This particular method is adapted from an email conversation with Michael Garcia.

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. If working with children, adult supervision is strongly recommended.

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% of the weight of fiber, or 2-4 rounded teaspoons for 100 grams of fiber. More mordant will increase the depth of shade.

Wheat bran: the recommended amount of wheat bran is 5% of the weight of fiber, or 4 teaspoons 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 have access to 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)

For wheat bran bath:

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

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.  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 (see top photo of yarns in tub as an example).

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

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 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.  The solution will be milky.

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 will notice some cloudiness and 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.

Notes:

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. As well, mordanted fibers may be stored damp in a plastic bag and refrigerated up to 7 days and cured or aged, as this also seems to increase the depth of shade in the dyed fibers. Mordanted fibers may also be dried and stored 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.

Aluminum acetate baths may be reused 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.