How to Prepare Fabric for Natural Dyeing: Scouring and Mordanting

Good natural dyeing starts long before the dye pot. If fibers and fabrics are not properly prepared, the dye takes up unevenly and the color has poor wash and light fastness. This guide explains the two preparation steps, scouring and mordanting, for both protein and cellulose fibers, and busts a few common natural dyeing myths along the way.

Which fibers can you dye naturally?

Natural dyes work on natural fibers. Synthetic fibers made from petroleum, such as polyester, do not take natural dyes well.

• Protein (animal) fibers: wool and silk.
• Cellulose (plant) fibers: cotton, linen, hemp and bamboo viscose.

Start with fabric that is undyed and free of coatings and softeners, such as our undyed fabric by the yard and dye-ready blanks. Read why this matters in why natural fibers matter for natural dyeing.

The two preparation steps

• Scouring: cleaning the fiber really well to remove grease and any substances from manufacturing, washing or conditioning.
• Mordanting: treating the fiber with a substance that lets the dye fix, or "bite". The word mordant comes from the Latin mordere and French mordre, "to bite".

The methods below are not the only ones, but they are tried and tested, and they are the methods used for many of the results shown on the themazi website. For more options, see our complete guide to mordants.

Safety first

"Natural" does not always mean safe. Read the safety notes for every product you use, and wear gloves and a dust mask when handling irritants or fine powders. Work outdoors or in a well-ventilated space, and never use dyeing equipment for cooking again.

How to prepare protein fibers (wool and silk)

Scouring

Soak the fiber for two hours in warm water with a little pH-neutral detergent. Rinse well, then dry it or keep it wet for mordanting.

Mordanting with alum

1. Weigh the dry fiber.
2. For every 100 g of silk, use 8–10 g of alum (potassium aluminum sulfate). For every 100 g of wool, use 8–10 g of alum and 7 g of cream of tartar.
3. Dissolve the alum (and cream of tartar for wool) in a little boiling water in a heatproof container.
4. Fill a pot with enough cold water to cover the fiber easily, and add the alum solution and the wet fiber.
5. Heat to a very gentle simmer, turn off the heat and leave the fiber to cool in the mordant overnight.
6. Squeeze it out well. Dye straight away, or dry it and wet it again when you are ready to dye.

More detail: how to mordant wool and silk.

How to prepare cellulose fibers (cotton and linen)

Scouring

Simmer the fabric for 90 minutes in a large stainless steel or enamel pot with a tablespoon of soda ash (sodium carbonate), then rinse. Or wash it on the hottest washing machine cycle with a tablespoon of soda ash in the drum. You will be amazed at the dirt that comes out if you do it in a pot!

Mordanting: the tannin and alum method

1. Tannin: weigh the fabric and use the recommended amount of tannin, usually 8–10% WOF (see each product page). Oak gall tannins add the least color of their own and are very rich in tannin; we also offer sumac, pomegranate and acorn. Most tannins are applied by soaking the fabric in the hot tannin bath and leaving it to cool overnight.
2. Alum: for every 100 g of fabric, use 15 g of alum and 2 g of soda ash. Dissolve each separately in boiling water. Fill a container large enough for the fabric with hot tap water and carefully add both solutions; it will fizz.
3. Add the damp, tannin-treated fabric and leave it for several hours or overnight, stirring now and then.
4. Optional: give the fabric a second soak in the saved tannin bath for deeper colors.
5. Dye straight away, or dry it and wet it again when you are ready.

More detail: how to mordant cotton and linen. Our cellulose mordant studio kit includes the tannin, alum and soda ash.

Are all oak galls the same?

Not quite. Read Catharine Ellis's experiment comparing oak galls, and our own oak gall tannin guide.

Myth busting

• Vinegar and salt are not mordants for natural dyeing.
• Most natural dyes need a mordant to fix properly, but a few, such as onion skins and other tannin-rich dyes, do not. See 4 natural dyes that don't need a mordant.
• Most berries, red cabbage, beets, black beans and purple carrots make stains, not dyes. They are not colorfast, even with a mordant. Don't dye with them; eat them instead!

Next step: choose your colors from our natural dyes and mordants, or read natural dyes: everything you need to know.