A mordant is a term meaning a chemical substance used in dyeing to fix the color, especially a metallic compound, that combines with the organic dye and forms an insoluble compound. Possibly derived from a Latin verb "mordēre", which means "to bite." When it comes to pretreating your item, mordanting is just as important as scouring. With the exception of Indigo, I always mordant my items, including silk, even though it is not required. For color longevity, a mordant is a must! Additionally, since we are using our earth's resources (dye, water, energy) we SHOULD take all the steps to ensure durable, long lasting color.
That being said, there are many mordants to choose from. My mordant of choice for cellulouse fiber is Aluminium Acetate (mineral based), though there are other options like Aluminium lactate (a newish mordant, which is manufactured from lactic acid from sustainable sources) and Symplocos Mordant (naturally alum rich dried leaves from the Symplocos cochinchinensis plant). Alternatively you can use a soy milk binder, though not a true mordant, it will to “proteinize” cellulose fiber. Binders (soy bean milk, egg whites, even blood) help to adhere pigment to the fiber, but the bond is not chemical and sits on the surface. Binders are not considered as durable compared to metallic salt mordants.
Supplies needed: fiber/item for dyeing, non-reactive (stainless steel) pot or bucket, scale, spoon or tongs, Aluminum Acetate, tannin, hot tap water, gloves
1. Immediately after scouring and fully rinsing/neutralizing your item, begin mordanting as follows. Using a scale and large container (a plastic bucket works well since we won't be using heat), weigh out tannin extract at 5% WOF. NOTE: When measuring powdered chemicals, always wear a dust mask. “Wet out” the tannin extract by slowly adding boiling water to the dry tannin powder and mixing it with a wooden spoon until it is a liquid consistency. You may need to work out some lumps until the tannin is completely dissolved. Fill your container with hot tap water, leaving enough room to add your fiber without overflowing. Make sure your fiber can float freely in the tannin bath. The tannin bath should look like a tan, milky liquid. While the fabrics are still wet from scouring, add them to the tannin bath. Allow your fiber to soak at least 2 hours, but for maximum benefit up to 24 hours in the tannin bath. Occasionally stir and move the fabrics with a spoon or tongs for an even tannin application. If you plan to leave your items in a tannin bath overnight, try to keep them submerged under the water level, as I have experienced dark spots (oxidation) on fabric that was floating above the surface.
After 2-24 hours, remove the fiber from the tannin bath. While wearing gloves, remove the fiber and gently wring out. Because the tannin affinity is weak at this stage, I do not rinse my fiber, simply set them aside after wringing. Tannin baths can be reused by ‘refreshing’ them, meaning you can save the existing bath and add 50% of the required tannin for the next bath. You can also dispose of the tannin mixture by neutralizing it (ph 7) before pouring it down the drain.
2. Next, wearing a dust mask and gloves, use a scale to weigh out 10% WOF of aluminum acetate for cellulose fiber. Slowly add boiling hot water to the AA and stir until it is a liquid consistency, this may require you to work out any lumps. Fill your container with hot tap water, leaving enough room to add your fiber without over flowing. Make sure your fiber can float freely in the alum bath. Add tanned fiber to the AA bath. Allow your fiber to soak at least 2 hours, but for maximum benefit up to 24 hours in the AA bath. Occasionally stir and move the fabrics with a spoon or tongs for an even alum application.
After 2-24 hours, remove the fiber from the alum bath. Alum baths can be reused by ‘refreshing’ them, meaning you can save the existing bath and add 50% of the required tannin for the next bath. You can also dispose of the alum mixture by neutralizing it (ph 7) before pouring it down the drain.
Optionally, repeat Step 2 of mordanting. Some dyers prefer to do multiple tannin and/or alum baths. When dyeing dark colors, more than one tannin bath is recommended. After your tannin and alum baths are complete, you can rinse and dry your fiber for storing. This is a good stopping point as the affinity with tannin and alum is strong.
Optional CHALK/ WHEAT BRAN POST MORDANT BATH:
Doing a chalk or wheat bran bath helps to remove any un-bonded mordant on the fiber. Excess mordant can dull your color. The chalk will form a chelation (bind) with the metallic ions. It is recommended to use 5% WOF, or 1 rounded teaspoon for 100g of fiber. Wheat bran does contain gluten, so avoid if allergies exist.
1. Immediately prior to dyeing, fill a container with hot tap water, leaving enough room to add your fiber without overflowing. NOTE: When measuring powdered chemicals, always wear a dust mask. Make sure your fiber can float freely. Add 2-5% WOF Calcium Carbonate (aka chalk) and fully dissolve in the water. Add your mordanted fiber for 15-30 minutes. Rinse thoroughly and proceed to dyeing. Doing the chalk/wheat bath immediately before dyeing serves two purposes: it removes excess AA and also “wets” your fiber in preparation for dyeing. This saves precious water!
Natural dyer, natural dye educator, maker and all around textile nerd.