How to Make Mordants for Natural Dyes

Use these recipes to make mordants for natural dyes.

Harvesting Color

Make beautiful natural dyes from plants with the help of “Harvesting Color.”

Cover Courtesy Artisan Books

Content Tools

Harvesting Color (Artisan Books, 2011) is the essential guide to natural dyeing and creating gorgeous color from plants. Author and master dyer Rebecca Burgess presents over thirty plants which yield stunning natural shades and illustrates just how easy the dyes are to make. In this excerpt taken from part one, “Getting Started,” see how to make mordants for natural dyes.

You can purchase this book from the MOTHER EARTH NEWS store: Harvesting Color.

Preparing Mordants For Natural Dyes

Mordanting your fibers before they enter the dye vat is also known as premordanting — this process can be done immediately before dyeing the yarns, or mordanted fibers can be left to sit for an indefinite period of time before they enter the dye vat. I find the best color results occur from letting the fibers sit for a week after coming out of the mordant bath before being dyed.

Mordant Recipe for Protein Fibers

This mordant recipe is useful for incorporating both powdered alum and iron. Most recipes in this book call for alum. However, several recipes, including fennel, sheep sorrel, and French broom, recommend using iron to prepare your fibers before dyeing, because it has a tendency to create deep green colors from dye baths that might otherwise yield yellow. Powdered iron or ferrous sulfate can be purchased from dye supply stores. Another option for iron is to make a solution from rusty objects (see Rusty Object Solution).

1. Weigh the material to be dyed. Measure out your mordant by calculating 10 percent of the material weight (for instance, to dye 10 ounces of raw wool, you’ll need 1 ounce of mordant).

2. Fill a stainless steel or enamel vessel with water and place over high heat. Bring to a boil. Add powdered mordant and dissolve thoroughly.

3. Reduce heat to a simmer. Add your protein fibers to the mordant bath and leave it in for 1 hour. Use a thermometer to monitor the water temperature — it should be within a range of 185 to 200°F.

4. Remove fiber and rinse prior to hanging to dry (see Note). In the case of wool, make sure the temperature of the rinse water is similar to the temperature of the fiber to avoid felting. The final rinsing stage removes any extra mordant that didn’t bond to the fiber. Unbonded mordant can release and bond to the pigment within the dye vat — leaving less dye available for the fibers.

Note: Keep in mind that fibers will absorb perhaps 50 percent of the mordant, so when rinsing the fiber, be sure to capture the wastewater and add it back into your mordant bath for reuse.

Rusty-Object Solution

A rusty object presents a very simple way to create your own iron mordant solution at home. Although you won’t know the exact ratio of iron to the weight of your fiber, with some experimentation you’ll be able to create a solution that works well. Using small objects such as old nails or screws that will easily fit into your vessel is important. I use a tall one-gallon glass jar with a lid to make my solution, but any glass, ceramic, or enamel lidded vessel that can hold at least a gallon of water will work.

1 gallon container with a lid
White vinegar
2 handfuls of rusty objects

Fill your container halfway to three-quarters full with water. Put 1 tbsp. of vinegar into the jar for every 1 c. of water, and add the rusty objects. Leave the mixture for a period of time so that the iron can go into solution. This will be a process you can observe by occasionally stirring your solution to see if the water has turned orange. During the summer months, the process will take from several days to a week; in the winter, due to the colder air temperature, the process will take several weeks. Once your water has turned a deep orange color, it can be poured into a bigger pot or dye vessel. Add extra fresh water to the vat, so that your fibers will be able to move about freely. Heat the iron water to 180 to 200°F. Add your fibers to the water and let sit on the heat for 60 to 90 minutes. Rinse in warm water, and then hang to dry.

Natural Mordant with Vinegar

Most dyes will not hold color over time with a natural mordant with vinegar; the exception to that rule is pokeberry, which requires a vinegar mordant. Carol Leigh of Columbia, Missouri, discovered this unique relationship between vinegar and pokeberry. The result is an extremely beautiful color, one of the best produced with a native North American species.

1. Fill a stainless steel or enamel pot with water. Add ½ cup of white vinegar for every 4 ounces of fiber.

2. Gently heat your pot over medium heat (160–180°F) for 60 to 90 minutes.

3. Remove the fiber and place it immediately into your pokeberry dye vat.

Tannins Solutions

If you live among oak trees, it’s easy to make your own tannin solution — the base ingredient is acorns, and they’re plentiful in the early fall.

Tannins can also be purchased in powdered form. To make a solution, dissolve 1 tbsp. for every ½ gal. of water.

1. Collect about 1 lb. of acorns. Shell them by pounding and cracking their exterior with a rock. Once the shell has been cracked, you can generally peel it off.

2. Place your peeled acorns into a food processor and blend them into a fine meal. Place the acorn meal into a cloth bag and hang the bag over a large glass jar or a plastic bucket (I use a gallon jar). Using your faucet or a hose, turn the water on gently and let it drain through the cloth bag and into your container.

3. Squeeze the outside of the bag, and you should see a thick cloudy substance release into your container — these are tannins. The first five minutes tend to release the most potent tannins, so this is the solution to save for later use for a fall dye starter, and for mordanting cotton.

4. If you wish to make acorn flour, you’ll want to release all the tannin from the acorn meal. The process of releasing the tannins can take many hours, so I recommend securing the bag to the faucet or hose and letting the water gently rinse the meal, and overflow from your bucket or jar for as long as it takes for the water to run clear.

5. To make your own acorn flour, spread the meal out to dry, and then blend it in a high-powered blender until it is a powdery consistency.

Mordant Recipe for Cellulose Fibers

Preparing cotton, hemp, linen, or ramie for dyeing requires an extra step after the fabric is mordanted in alum. Cellulose fibers, or plant-based fibers, will typically dye lighter than protein fibers like wool will. A second mordanting, this time in tannin solution, will amplify and deepen your dye results.

1. Complete the Mordant Recipe for Protein Fibers, using the 10:1 fiber to alum ratio. You can either hang the fibers to dry overnight or continue immediately with the application of tannin.

2. In a large pot, dilute your tannin solution with water. Heat the solution on medium heat until it reaches between 180 and 200°F. Add the cellulose fibers and let sit on the heat for 1 hour.

3. Rinse well and hang to dry.

Read more from Harvesting Color:

How to Make Natural Dyes
Master Dye Bath Recipe
Fiber Preparation for Dyeing Yarn
Enhance Dye Colors With Afterbaths

Excerpted from Harvesting Color: How to Find Plants and Make Natural Dyes by Rebecca Burgess (Artisan Books). Copyright © 2011. Photographs by Paige Green. Buy this book from our store: Harvesting Color.