Discharging Indigo
February 2024
This is an experiment in discharging indigo from a dyed textile that uses methods and recipes provided by Joy Boutrup and Catharine Ellis in their book, The Art and Science of Natural Dyes. Potassium permanganate, an oxidation agent, is used to breakdown indigo in a textile, which then converts into manganese dioxide. The manganese dioxide is then removed by immersing the textile in a citric acid solution, leaving the textile white or faintly blue.
Potassium permanganate is a potassium salt of manganese that appears near black in crystal form and appears a vibrant violet when dissolved in water.
To create the solution, 2 grams of potassium permanganate are dissolved in 1000 milliliters of water. This ratio can be scaled up or down depending on the size of the textile being used. Once dissolved, the solution is viable for an hour or so and then will begin to lose efficacy.
When the solution is ready, the textile is immersed for about 5 minutes. The textile will shift from blue to purple and then to brown. Once brown, the textile can be rinsed and then placed into a citric acid solution (40 grams of citric acid to 1000 milliliters of water).
The textile will slowly shift from brown to a faint blue or white after 10 minutes in the solution. This process can be repeated as necessary. When the desired shade is obtained, the textile needs to be neutralized in a chalk (calcium carbonate) bath given the high acidity of the citric acid solution. After this step, the textile can be rinsed and washed with a neutral detergent.
The image below (left) shows the textile being removed from the potassium permanganate solution. The color appears reddish brown due to the potassium permanganate converting into brown manganese dioxide. Once rinsed after the potassium permanganate bath, the textile appears a yellowish tan where the indigo has been discharged. In the picture below (right), the textile is being placed into the citric acid solution to remove the manganese dioxide.
The three images below show the slow shift from brown to white in the citric acid solution. This shift occurs over the course of 10 minutes. Unlike the potassium permanganate solution, the citric acid solution may be saved and stored for a later date.
The images below show the final result after stripping color from dyed textiles. While this experiment was mostly concerned with indigo, we decided to test a madder-dyed swatch to see what would happen. Curiously, madder was also discharged by the process. Even before reaching the citric acid solution (known to strip color from mordant dyes), the potassium permanganate had discharged quite a bit of color. We don't know the science behind why this also works for mordant dyes (at least for madder) but nonetheless provides another tool for creating various results with natural dyes.
Bentonite clay can be used to thicken the potassium permanganate solution for printing applications. The thickness of the solution, the weight of the textile, the density of its weave or knit, and whether its dry or damp will affect the outcome. The thickened solution is best used fresh but may be kept for a day or two in an airtight container.
We decided to play around with the paste by discharging our initials on our indigo-dyed Chainstitch Tee. To create sharper edges, we used a paste with a pudding-like consistency and applied it to a dry tee. The paste remained on the tee for about 30 minutes. We then rinsed the tee and soaked it in citric acid for 10 minutes.
Below is the final product of printing on our tee. We didn't get a pure white, which isn't surprising given the weight, density, and dry state of the textile. For the other two swatches, we played around with different paste thicknesses and applying on a wet or dry textile.
Discharging indigo with potassium permanganate may also be used to create shades of brown on cellulose fibers where the indigo has been discharged. To obtain these results, the textile is placed in a fructose solution (50 g/L), rather than the citric acid solution, after being immersed in potassium permanganate.
For this process, the textile should be immediately placed into the fructose solution as opposed to being rinsed between steps. The sugar stops the oxidation process, resulting in a light brown hue.
To achieve deeper browns, the textile may be steeped in tannins before being placed in the potassium permanganate solution.
The image below (left) shows permanganate brown without any tannin treatment. The fructose solution prevents further oxidation and protects the textile from any long-term damaging effects of potassium permanganate. The other image below (right) shows a textile that was treated with tannin before immersing in the potassium permanganate solution, resulting in a much deeper brown color.
