A little over a year ago I bought some indigo seedlings from Vibrant Valley Farm and I’ve been caught up in the magic of this plant ever since. It’s possible to get beautiful blues along the reaction pathway from indican (the colorless precursor stored in the leaves), but to get the most consistent color on cotton, a “vat” is required. You build a vat by raising the pH to just the right level and using sugar or microbes to remove oxygen and reduce blue indigo back to yellow leucoindigo.

And so, of course, I was curious if it would be possible to make my own pH indicator. Could I use another plant’s color to navigate my way to a perfectly balanced vat? I remembered from my time as a science teacher that red cabbage had been fun to work with, and sure enough, there were excellent instructions available to guide my explorations and beautiful graphics to translate color to pH. And an old T-shirt worked great as as a carrier.

This year, having tracked down a bit more information about the behavior of leucoindigo molecules, I’m starting to have a better sense of what might be happening below the surface of my vat at different pH levels. I may have spent a little too much time fiddling with this graphic, but it’s a fun way to connect the red cabbage colors with the equilibrium behavior of leucoindigo as it moves between the neutral insoluble form, the soluble form that is an excellent dye, and the very soluble form that is too highly charged to dye cotton.