Roasted coffee beans (Coffea arabica) create rich brown dye. The darker the coffee bean has been roasted, the darker the dye and the more intense brown you will be able to achieve. Espresso beans are roasted darker than regular beans. For even darker coffee dye, you can steep the coffee and grounds for an extended period in a light-proof, lidded container, so it can age without growing mold. You can also save your coffee grounds to use with warm neutral colors; the grounds can yield a warm beige that can soften bright colors and create an antiqued tone.
Depending on how dark the coffee roast is and the delicacy of the fiber you are using, you can use hot-water extraction or cold-water extraction. No mordant is necessary when using coffee dye on both animal and plant-based fibers, although the addition of a mordant can improve both light and wash-fastness and extend the range of rich browns. If you prefer tea to coffee, it works just as well!
Excerpted from "The Handbook of Natural Plant Dyes: Personalize Your Craft with Organic Colors from Acorns, Blackberries, Coffee and other Everyday Ingredients" by Sasha Duerr, published by Timber Press. Image by Sasha Duerr.
Create a coffee dye bath dark enough to color your fiber the desired shade of brown. In the dye pot, the bath should be deep enough to allow the fiber to move around freely.
Add your soaked fiber to the dye pot. Slowly heat the fiber in the coffee bath to simmering point, 180°F (82°C), and simmer for 15 or 20 minutes. Turn off the heat and let fiber steep until the desired shade has been reached. Leave the fiber overnight if you want a deep brown color.
Wash the fiber with pH-neutral soap. Rinse thoroughly. Hang to dry.