Clasping, Pinching, and Biting: A Mordanting Primer

Our gardening and dyeing season has begun in earnest at the Janice Ford Memorial Dye Garden, with  yarrow and indigo filling our inaugural pots. We’ve harvested one of our madder beds, which is really exciting!  Madder root takes three years to mature into a color-producing dynamo, and three years it has been since we planted our bed. Check back for an upcoming post on processing and dyeing … but, before we talk dyes, we need to talk mordants.

You may be able to color fiber with a natural dye but, for the most part, without an intermediary to fix the two together, disappointment looms. Wash it and farewell color. The intermediary is the mordant, a fascinating word which, according to the Oxford English Dictionary, was first recorded in 12th-century French. Long before obtaining its dye connotation, a mordant was a buckle or clasp, i.e., something that fastened two things together. Later, 19th-century zoologists used the term to describe crab and lobster pincers. Can you see the pattern emerging? In adjective form, the medieval-French mordant(e) meant biting or caustic, referring both to the corrosive properties of the thing described and a type of human wit. For the etymologically curious, the first  use of the word in a written-English-dyeing context occurred in 1791 in W. Hamilton’s translation of Claude-Louis. Berthollet’s Elements of the Art of Dyeing.  We’ll leave Etymology Land now but leave you with a mnemonic for later recall — two common mordants in the dyer’s toolkit (alum and tannin), bracketing one uncommonly mordant human wit.

A Definition for Natural Dyers

Following Alpenglow Yarn:
A mordant is a chemical that becomes part of the molecular bond between the fiber and the dye.  Primarily these are metal salts … You can think of a mordant as a molecular glue.  In general, dyes and fibers have a weak affinity for each other. If you tried to dye yarn without a mordant, the color would be very dull, and it would wash out promptly and fade easily. A mordant sticks to fiber well, and it also sticks to dye well. So you essentially “dye” the yarn first with a mordant, then repeat the process with the dye itself. This results in a strong bond between dye and fiber, which is fast to both washing and light exposure (in varying degrees for various dyes and mordants and combinations thereof). The mordant also affects the final color of the dye.

Of the several mordants available to natural dyers, we will focus on alum (potassium aluminum sulfate) and tannic acid because they are our basic, go-to compounds for mordanting protein (animal) and cellulose (plant) fiber. There are likely as many mordanting methods as there are dyers and, at the end of this post, you’ll find a short bibliography of sources we’ve found useful. We encourage you to think critically about mordanting … about everything really … with the goal of understanding what you’re doing. Catherine Ellis has addressed this topic on her blog and it’s well worth a read. While you can certainly follow a set of instructions and achieve good results, your experience will be enriched by study and experimentation. Keep a record of what you use, what you do, and how it turns out. Strategize about what you might do differently next time. Seek out teachers in person, in books, online … consider it a learning opportunity!

Our Instructions

Our dye project is fortunate to have the leadership and guidance of expert and teacher, Donna Brown, and the guidelines that follow are hers, adapted with permission. A note on mordanting safety: while alum and tannic acid are considered relatively safe, care for yourself by wearing latex gloves and, if particles are likely to become air born, invest in air filter masks or a respirator. If possible, work outdoors for good ventilation. Alpenglow Yarn wrote a well-researched post on mordant safety, which we highly recommend.

Mordant Recipe for Protein Fibers: llamas-97337_960_720

Step 1: Weigh your dry material to be mordanted and record your weight of goods (WOG). We generally use the metric system.

Step 2: To facilitate even dyeing, clean or scour fiber to remove any oils, dirt, or processing chemicals. Soak in hot tap water and with a pH neutral liquid detergent (synthrapol, Dawn Original Blue, etc) at about 20 ml or 2% by volume. Rinse and repeat until water is clear. To avoid felting, do not agitate or shock fiber with sudden temperature changes. Fabric can be washed in a machine per washing instructions. You can air dry your fiber for mordanting another day, or proceed to do it right away. Fiber must be wet before proceeding.

silkworm-931555_960_720Step 3: Weigh alum based on your dry weight of goods. Experts differ, suggesting a range from 7% WOG to 20% WOG for alum on protein fibers.  Donna has had success mordanting sheep wool with 7 – 10% and silk at 20% WOG. Different protein fibers may require an increase in the percentage to achieve dark colors; for example, Donna has had better success dyeing alpaca with 15% alum on the WOG.  It’s a good idea to sample with the fiber and water you are using.

Before mordanting, soak fiber for at least one hour in warm water with a touch of soap (as above). Rinse before adding to mordant pot.

Add mordant to a pot full of warm water and dissolve completely before adding fiber.

Step 4: Slowly bring pot temperature up to simmer (approximately 160 degrees F) for one sheep-275928_960_720hour, then let stand without heat for a minimum of two hours. Stir at least twice after removing pot from heat. Do not boil wool as felting may result!

Step 5: Rinse cooled fiber lightly in warm water to wash off the mordant liquid, squeeze gently (never wring), and proceed with dyeing, painting or surface design. Fiber may  be dried at this time and stored until you are ready to dye. It’s a good idea to label fiber, noting that it has been mordanted.

Mordant Recipe for Cotton and Cellulose Fibers:

Step 1: Weigh your dry material to be mordanted. Record your WOG.


Step 2:  Scour your fiber. Prepare a pot of warm water. For every kilo or 1000g of fiber add :
a) a neutral liquid detergent at 20 ml or 2% WOG; and,
b) soda ash (sodium carbonate) at 80g or 8% WOG.
Simmer one to two hours. Multiple scourings may be necessary to completely clean the fiber. If your water turns brown, repeat this step.

Step 3:  Apply tannin. Gallic tannins, i.e., gall nut, sumac, tara, and tannic acid are the best for fixing mordants on cellulose fibers. Tannins block ultraviolet light and therefore increase the light fastness of dyes.


Add tannin at 10% WOG to a vessel with enough warm water to allow fiber to float freely. Soak for one to two hours, then rinse in cold water and dry for later mordanting or proceed to Step 4. If you’re drying your fiber, remember to label it, noting that tannin has been applied.

Step 4: In one container, dissolve alum (potassium aluminum sulfate) in water at 12% WOG. In a second container, dissolve soda ash (sodium carbonate) in water at 1.5% WOG.


Step 5: Mix the two solutions together in a vessel large enough to permit fiber to move freely. Add hot water (90-140 degrees F) to cover your tannin-treated fiber. Remember, the fiber must be thoroughly wet before this stage so plan ahead and soak for a few hours.

Note: the mixture can produce a lot of bubbles; wait until they subside to add fiber. If the solution remains hot (i.e., it’s in a pot on the stove), soak for two hours. If in a bucket and/or not hot, soak for six to nine hours. Stir occasionally for even distribution.

Step 6: Rinse fiber in cool water and dry. Label as desired.

Mordant Reuse and Disposal

If you find your self regularly mordanting a particular protein/animal fiber, you can reseed the pot after a mordant session by adding 50% alum per WOG of the new material to be processed. Add enough water to cover fiber. Donna Brown says you can repeat this re-seeding four to five times before the bath becomes too murky to use.

Regarding cellulose/plant fibers, tannin baths can be stored and reused. When you’re ready to process new material, add additional tannic at the rate of 5% WOG and enough water to cover.

When the time comes to dispose of your mordanting solutions, the US Environmental Protection Agency provides a link to departments in each state and territory that can advise you. Colorado residents, contact the Department of Public Health and Environment. For more information, Jenny Dean provides a handy chart covering disposal and other aspects of several mordants in her excellent book, Wild Color: The Complete Guide to Making and Using Natural Dyes. 

And now, bring on the dyes!

Suggestions for Further Reading

Alpenglow Yarn. “Mordants and Natural Dyeing, the Great Debate.” Blog post. November 11, 2014, accessed June 5, 2016

Brown, Donna, Diane de Souza and Catherine Ellis. “Mordanting Cotton and Cellulose — Successful Methods,” Turkey Red Journal 19:1, Fall 2014., accessed June 8, 2016.

Cardon, Dominique. Natural Dyes: Sources, Tradition, Technology and Science. London: Archetype Publications, Ltd., 2007.
Pages 4-5 and 10-15 discuss mordants and describes mordanting processes for wool, silk, and plant fibers.

Dean, Jenny. Wild Color: The Complete Guide to Making and Using Natural Dyes, New York: Watson-Guptill Publications, 1999.
Pages 36-45 discuss various mordants, provide instructions for protein and cellulose fibers, and address safety and disposal.

Ellis, Catherine. “The Importance of Thinking for Natural Dyers,” Blog post. Natural Dye: Experiments and Results. February 5, 2016, accessed June 6, 2016.

MAIWA. “Natural Dyes — Mordants, Part I,” Blog post. January 11, 2013, accessed June 9, 2016.

MAIWA. “Natural Dyes — Mordants, Part II,” Blog post.
January 23, 2013, accessed June 9, 2016.

MAIWA. “Natural Dyes — Mordants, Part III,” Blog post.
June 27, 2013, accessed June 9, 2016.























Author: Janice Ford Memorial Dye Garden

The Janice Ford Memorial Dye Garden is a joint project of the Denver Botanic Gardens and the Rocky Mountain Weavers Guild, established by a donation from the family of Janice Ford. Janice was an enthusiastic and energetic dyer, weaver, and seamstress who passed away too young in 2011. The garden has been flourishing since 2014, enriching and coloring the lives of visitors, artists in many media, and especially those whose privilege it is to tend it. The garden is located at Denver Botanic Gardens at Chatfield Farms. From June to September, we are there most Thursdays, 9-12, to weed, harvest and dye. Visitors are welcome to stop by to see what we're up to!. Admission is free to Denver Botanic Garden members, with a $5.00 fee/car for non-members.

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