Mordants
In order for dyes to fully stick to fiber, they require a fixative, known to dyers as a mordant. Mordants help the colors from dyes chemically bond to fibers. The word, itself, comes from the word mordere, meaning “to bite” in the Latin language. This relates to the function of a mordant: it assists the color in “biting” into the fiber so that it can resist changes from light exposure, washing, or rubbing.
The process of mordanting can occur at any point during the dyeing process, but it is important to know when and also which mordant will be best depending on the type of fiber being used. It is also important to understand that mordants can influence the final color of the dyed piece. The below chart from the book, Botanical Inks by Babs Behan, illustrates the differences seen when using different types of mordants on different types of fibers.
For my project, I have chosen to use oxalic acid, a natural plant-based mordant that can be extracted from rhubarb leaf. I chose rhubarb leaf because of the natural and renewable qualities that it holds, unlike synthetically made mineral-based mordants. Rhubarb leaf is also safer to dispose of and was already available to me on my family farm, unlike other commonly used mordants. The drawback of rhubarb leaf and plant-based mordants in general, however, is that they very often leave a tint of color if used before dyeing. It won’t be an issue if deep colors are what the dyer desires, but light colors may be harder to achieve when using these mordants.
Alternative plant-based mordants that can be used when dyeing fibers include tannic acids, which can be found in oak galls, oak bark, acorns, chestnuts, and other tree barks and nuts. These work best with plant fibers, while oxalic acid (which can also be found in borage and certain seaweeds) is best when working with animal fibers. Mineral-based mordants can also be used, the most common ones being iron and a combination of alum (potassium aluminum sulfate) and an assist (either cream of tartar or soda ash depending on fiber-type). Both of these metals are safe to use in small quantities and if used properly, should be fully absorbed by the fiber so that none is left within the water and it is safe for disposal. Either way, however, is it important to use safety when working with and disposing of any mordant, whether it be plant or mineral-based.
Safety is an important consideration for my project because even though I am working with a plant-based mordant, oxalic acid can be highly toxic. As the acid is heated, it luckily gets broken down and becomes non-toxic and safe for use as a mordant, but the heating process of the raw leaves is still of concern to me. The fumes from the heating process are toxic if breathed in, and since I am working out of my tiny apartment kitchen, I will need to figure out how to ventilate the space while carrying out this part of the project. I am planning on leaving windows open, having the kitchen fan on, and of course, wearing a mask and gloves if interacting directly with the leaves. However, if I figure out a way to be able to work outside when extracting my mordant, I will surely do that instead!
New Materials!
To expand my natural dye materials, I revisited my local Goodwill and lucked out on some good finds. The best find of the day was an old scale, something I was in search of but didn’t get my hopes up to find. This scale will be a perfect aid in the mordanting process, as I will be able to take proper measurements of fiber and rhubarb leaf values to get the mordant amounts correct. I also found a large jar for storing the mordant mixture. I am not sure if it will be large enough for all of the mixture but I also may carry out the mordant process in multiple stages instead of all at once, so I am hoping the jar is perfect for a single batch. Finally, I bought a fun pair of gardening gloves for future foraging adventures, especially ones that involve the collection of nettle.
The Mordanting Process – Rhubarb Leaf
Materials
- Fiber (washed, scoured, and dry)
- Rhubarb leaves
- Scale
- 2 large pots
- Long-handled spoon
- pH neutral soap
Process
1. Weighing the Fiber
The weight of the fiber you are mordanting is important in determining the amount of rhubarb leaf to use in the mordant solution. As a general rule, use 200% the weight of the fiber (WOF) in rhubarb leaf when making a mordant. For example, I had around 42 grams of washed and scoured wool, so I used 84 grams of rhubarb leaf in my mordant solution.
2. Allow Fiber to Soak
Soak the fiber in a large pot for at least an hour, although 8 to 12 hours is ideal.
3. Wash and Cut Rhubarb Leaves
Wash and cut (or shred) the leaves into tiny pieces. Place them in a separate pot so that they can be fully submerged in water.
4. Boil Leaves in Pot
Pour enough boiling water over the leaves to cover them. Then bring the water to a simmer and cover the pot with a lid. Simmer for 1 hour.
5. Strain Out Plant Material
After the hour is over, let the solution cool off before straining or scooping out the plant material. Once you have the final mordant solution, it can either be stored in jars for later use or transferred into a pot that is large enough to hold the fiber you are mordanting. The fiber should be able to move around freely within the solution. More warm water can be added to the pot if there is not enough space.
6. Add Fiber to Mordant Solution
Once the fiber has been added to the mordant solution, bring the pot to a simmer for another hour with lid cover. The fiber should be stirred occasionally with the long-handled spoon. This releases any air bubbles trapped in the fiber. It also moves the fiber around so that the mordant can reach all parts of it, as some of the wool may have been at the surface or touching the sides of the pot.
7. Wring Out Excess Liquid
After the hour is over, let everything cool before moving the fiber out of the solution. Wring out any excess liquid within the fiber.
8. Rinse And Wash Fiber
Rinse and wash the fiber with cool water and pH neutral soap. Rinse again to remove all soap.
9. Dry the Fiber
While the fiber can be used in its wet state for dyeing, I chose to dry mine for later use. Make sure to air dry the fiber somewhere warm and out of direct sunlight.
It was interesting to see how the rhubarb mordant interacted with the wool, dulling the color from a lovely snow-white to a grayish brown. This showed how using a rhubarb mordant might not be desirable for some dyers depending on the color they are trying to achieve.