Mordanting is the process of soaking your yarn in a metallic solution in order to allow the fibers to accept and hold on to natural dyes. If you have ever splashed grape juice, red wine or red beet juice on your clothes you know that although it will produce a stain, the stain does not keep the original deep color. Mordanting opens up the fibers so that natural dyes can truly take and be more permanent. The word mordant originally came from a French word meaning “to bite.”
In more ancient times, dyers would have several different all metal pots. Dyers would first soak the fibers in warm solutions in an all copper, all iron, or all tin pot. The fiber would then be ready to receive the natural dyes. Tin and aluminum pots today usually do not provide enough mordant to keep your dye from fading. If you are lucky enough to have a large all-metal pots to use for dyeing, be sure that you do not use your dye pots for food preparation. Even many natural dyes can leave toxic chemicals behind that are not safe for food consumption.
If you have a non-reactive pot that you can dedicated to dyeing, a good mordanting process to begin with at home is using alum. Yes, the same binding agent that is available in the spice and baking section at your local grocer is an excellent mordant for natural dyes.
It is best to begin with clean, white or light colored yarn. If the yarn is in a tight skein or ball, you will want to put the ball into a long hank. Your local yarn store may have a niddy-noddy and be able to help you do this. If not, pull the yarn out of the ball or skein and wind up as you would a rope or electrical cord.
If you spun the yarn yourself you can be sure that it does not already have any special finishing agents applied to it that will affect the dye process. If you are like me and purchase most of your yarn for dyeing, you will want to gently wash your yarn with a very mild detergent and rinse it very well to remove any possible finishing chemicals that the manufacturer may have applied.
The next step is to allow the yarn to soak in cool water so that it remains wet when you are ready to add it to your mordant pot. Preparing your mordant pot depends on if you are doing animal or plant fibers.
Animal Fibers For every 4 ounces of animal fiber yarn, add 1 tablespoon of alum and one tablespoon of cream of tartar to a jar of very hot water. Stir the solution until the alum and cream of tartar are thoroughly dissolved. Add this solution to your pot already full of water. Stir in the solution thoroughly. Now carefully add your hank of yarn and slowly bring the pot to a simmer. You want to avoid stirring as much as you reasonably can at this point, because it will create a tangled mess of your yarn. Let the yarn simmer for at least an hour. After you have allowed adequate mordanting time, take the pot off the burner and allow the water to cool. After the water has cooled, remove your yarn, rinse it and dye it immediately or store it in a sealable plastic bag to be dyed in the very near future. I know dyers who keep mordanted yarn in the freezer, so they need only defrost their yarn when they are ready to dye it.
Plant fibers also need a tannic acid treatment after being treated with alum. Begin by taking your plant fiber yarn and soaking it in a lukewarm solution of alum, following the amounts above. You just need to soak your plant fibers, not simmer them. Let them soak for minimum of 8 hours, but a full day is really best. Remove your yarn and rinse.
You have several choices to prepare your tannic acid solution. You can use pomegranate rinds, oak galls, sumac leaves, acorn shells or juniper needles. Make sure these items are dried and either powdered or crushed into small pieces. Simmer a large handful of your tannic acid herbs into 2 gallons of water. Allow the solution to cool and then put your alum mordanted plant fiber yarn into the solution and allow it to soak at room temperature for a minimum of 12 hours, on up to a few days.
If you don’t have access to any of the tannic acid plant or herb material listed, you can order tannic acid powder from various suppliers on the internet. You can use 1 tablespoon of powder to two gallons of water, and then soak your alum mordanted plant fiber yarn in the solution for 12 hours to a few days.
Your yarn will be well ready to accept most natural dyes. Part of the beauty and joy of using natural dyes is that many dyers cannot predict exactly what color and shade their dyed yarn will come out. The many variables created between the yarn fiber, the mordant, the dye plant, the growing season, soil conditions, etc. all affect the final color.
Buchanan, R. (1995). A Dyer's Garden: From plant to pot. Interweave Press.
Mordanting notes for natural dye day. (n.d.). Retrieved from http://www.fairnet.org/agencies/weavers/mordant.html
Duerr, S. (2012). The handbook of natural plant dyes, personalize your craft with organic colors from acorns, blackberries, coffee, and other everyday ingredients. portland: Timber Pr.