How to Mordant Animal 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. 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 WOOL & ANIMAL FIBERS

Our preferred method of mordanting animal fibers is with aluminum sulfate and cream of tartar.

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 Guinea, West 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% WOF, or 1 scant Tablespoon for 100 grams of fiber. Note that you can go up to 20% WOF, or 1 Tablespoon + 1 teaspoon per 100 grams of fiber. So, 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% WOF, 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. 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.

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)

How to mordant

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.

How to mordant

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.

How to mordant

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

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

Reusing the mordant bath to save water and alum

Many dyers will reuse their alum bath for multiple mordant sessions to save water and mordant. You may reuse aluminum sulfate baths 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.

Storing mordanted fibers

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. For longer storage, 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. My unscientific experiments show that mordanted animal fibers hold the mordant for 5+ years, while silk seems to hold it for about a year or two.