In the context of this web site, mordanting is adding a substance to the dye source to influence it–that is to bringing out characteristics that may be otherwise hidden or suppressed. That substance is the mordant. A mordant does not serve as a color source on its own.

Mordants are commercially available, commonly in the form of salts from metals. These may be recognized by their distinctive colors. These mordants are listed in  order of relative toxicity, highest to lowest: chrome, cobalt, iron, copper, and aluminum. Aluminum salt, also known as alum, is used in making pickles, etc., and may be purchased in most grocery stores. Other items I will lump into this category of mordants for our purposes are cream of tartar, baking soda, and vinegar. The later serve to change the alkalinity and acidity, respectively, of the dye–another property that influences the final color.

Commercially available mordants may be recognized by their distinctive colors. Position your cursor over each image to the right to activate the rollover.

Tannin is commonly found in many plants and can function as a mordant. It can also be purchased through chemical and dye-supply stores in a more refined state as tannic acid.

When using commercially prepared mordants take care with how you use, store, and dispose of them. Remember, many of them are toxic, especially if allowed to build up over a period of time. The methods presented below of applying the dyes with brushes allow for less waste and therefore fewer toxins released into the environment.
When cooking up a juice dye, containers other than glass or stainless steel may also be used and the metals from which they are made may be employed to exert an influence on the ultimate color of the dye in the form of a mordant. An old cast iron pot, a copper jug, etc., work quite well.  To change the acidity of your dye try using citrus fruit, such as limes, instead of commercial vinegar. Your results may not always be as predictable, but your work will never become monotonous!
Most dyers mordant the cloth and then apply the dye as two separate steps. The advantage is that the mordant has a chance to bite into the fiber, so that when the color is applied, a maximum amount of bonding takes place.

I prefer to first dissolve a very small quantity of mordant in warm water. Then, after approximating how much dye I will need for my project, add this mordant solution to my larger container of dye. By adding the mordant solution a little at a time to the dye, you can actually watch it change color. Once you can see a change in the color of the dye there is no danger of adding too little mordant. Too much mordant will tend to take most colors to a brackish tone and may also tend to weaken the fiber in the long run.

Test the mordant/dye color on the selvage of your sized cloth by applying a little with a small brush and allowing it to dry.  Adjust the concentration as necessary.

Now that you have the desired color in sufficient quantity for one application you are almost ready to brush it on the cloth. But before doing so you should increase the volume of your dye by the actual number of coats you plan to apply. (Plan on a minimum of two to three coats.) Add room temperature water to the dye solution to increase the volume. Applying multiple coats will help to insure even coverage and reduce streaking. Once all your coats have been applied, the color should have the same depth as the original test color.

If you find the right color with your dye/mordant mixture, but would like a darker shade, adding more mordant alone won't help. Either add a greater concentrate of dye, with more mordant; or (assuming you have a sufficient volume of dye solution) plan on applying extra layers until you have the color character you are seeking.
I prefer not to carry mordants for resale. Check the recommended sites on my blog for suggested resources.

copyright John Marshall, 1992
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