FEEDBACK FRIDAY: Indigo Vat pH, Painting & Reusing Mordant Baths

This week on FEEDBACK FRIDAY: The science of pH and your indigo vat, painting with indigo flowers and reusing that mordant bath

Every week for FEEDBACK FRIDAY, we are emailed with questions from our natural dye community asking simple and complex questions that we thought might be worth sharing. Of course, all of your burning questions are answered by natural dyer in chief, Kathy Hattori, Founder of Botanical Colors.

After adding a fresh mother to my vats, the pH is always super high, like 12+. I usually have to add A LOT of vinegar to the vat to get it down to 11, even displacing lots of vat liquid to fit the vinegar in. Just curious why this happens and is there a way to combat this while making the mother solution? Could it be the water I’m using?

If your pH is consistently high using the 1-2-3 method, try reducing the amount of calcium hydroxide and fructose  by 10-20% and see if your indigo vat balances and reduces.

Method 1

Create the mother stock using 100 grams of indigo powder, 160 grams of calcium hydroxide and 240-300 grams of fructose. So rather than being a 1-2-3 indigo vat, you are making a 1-1.8-2.4 vat. This is one way to lower it but still have the vat work. If you find you need to increase the calcium hydroxide, just add a bit more to your vat, stir and measure the pH. You will need to experiment and determine the best amount of calcium hydroxide to use.

Method 2

Another method is to increase the water volume of your indigo vat. For example, add a quart of your mother stock to a 15 gallon bucket of water.  The water pH will “dilute” and lower the overall vat pH.  I don’t have any exact amounts of how much your pH will change but it is something you could test.

Method 3

Use a stronger acid to lower the pH. You can try citric acid and see if you need to use less; however, I’m a proponent of adjusting the amount of calcium hydroxide and customizing the 1-2-3 recipe for your needs.

Is there a way to make permanent paint/ink from the indigo flower?

The oxidized indigo flower is a great base to make a paint. Simply combine with gum arabic or a good watercolor medium. You may want to grind (mull) the pigment and medium together if you are a hardcore paint maker. You can also combine the indigo flower with soymilk, a la John Marshall. I don’t know if it can be considered “permanent.” Longevity probably depends on the medium used, and the paint is better suited for decorative effects on paper or fabrics that won’t be washed frequently.

Once a fiber has been mordanted, dyed, and washed – let’s say you want to redye the fibers. Do you need to re-mordant? Does laundering remove the mordant???

You normally do not need to remordant if you want to overdye. If it’s been a long time between the initial dyeing and overdyeing, (like several years), then I would remordant.

Can you reuse an aluminum acetate bath in the same manner as reusing an aluminum sulfate bath?

Yes, you can recharge multiple times. We estimate using 50% of the amount required to recharge each time. For example:

  • The first aluminum acetate bath requires 10 grams of aluminum acetate. Mordant as usual.
  • The second round requires 10 grams total, so add in 5 grams aluminum acetate to the existing bath and mordant as usual.
  • The third round requires 10 grams. Add in another 5 grams of mordant to the existing bath and mordant as usual.
  • You can proceed until your bath becomes cloudy or becomes highly discolored. Then discard and use a fresh bath.
  • The bath is good over several days if kept covered and in a cool place.

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