What’s the difference between a mordant and a modifier in dyeing?
Are you ready for another episode of Meagan’s Soap Box?
Vinegar is not a mordant. There, I said it. And it is definitely NOT a mordant for natural dyes. Want to argue? You can come fight me in my driveway.
Like with many products that market “natural” products to us, just because it has the word natural in it, doesn’t automatically mean safer or good for the environment. Dyeing is a chemical process, whether we talk about natural dyeing or dyeing with synthetics. Chemistry is at work here.
I’ve heard and read many articles by professional dyers which call for vinegar or ammonia to be used as mordants. With respect to their wide range of skills and knowledge, no. This is incorrect and it drives me absolutely crazy. It doesn’t help the next generation of dyers understand how and why dyes work.
A mordant is a substance, usually an inorganic oxide that creates a bond between the fiber and the dye. Vinegar and ammonia are modifiers. A modifier is anything that shifts the color or can help a mordant be more effective.
Examples of mordants include alum (commonly used in pickling), iron salts, tin, copper sulfate, and chrome. While some mordants, like alum, are fairly innocuous, other mordants like copper and chrome can be very dangerous, especially in powder form, which can be inhaled.
There is a whole group of dyes called “acid dyes.” If you’re new to dyeing wool yarn, you most likely used dye brands like Jacquard, Dharma, or Greener Shades. The dye powder already includes metal salts, which act as the mordant. When we add vinegar or citric acid to the dye, it lowers the pH, which assists the chemical reaction between the metal salt and the fiber.
Wait, so what does a mordant actually do? For the most part, dye molecules don’t directly connect to fiber molecules. Without a mordant, dye molecules will sit on the surface of the fiber and can be washed away. You may start out with a bright color, but as the textile is washed, more and more of the dye molecules are washed away. The textile will fade.
The mordant creates ionic bonds with both the fiber and the dye molecule, acting like the glue in the middle that sticks to both.
As always, I said most mordants are metal salts. There is a group of mordants called tannins or tannoids. These are plant-based mordants that can create the bond between the fiber and dye molecule.
These can be found in black walnuts, acorns, oak galls, grapes, tea, marigolds and in many plants. They create a bitter taste, making seeds and leaves unpalatable for animals that might eat them.
Tannins are often used as dyes in their own right, offering a range of yellows to dark browns, but can also act as the connector between a dye molecule and fiber. The resulting color will be impacted by tannins, usually darkening or muddying the color. However, imagine using marigold to get a bright yellow and then overdyeing that with some indigo. You’d get a gorgeous green!
As I said earlier, anything that shifts the pH has the ability to either alter the color and/or assist in the chemical reaction. Use all the vinegar you need and want! It is there as a tool! But don’t let me hear you call it a mordant!
