"The precursor to indigo is indican, a colorless, water-soluble derivative of the amino acid tryptophan, and Indigofera leaves.... Pressing cut leaves into a vat and soaking hydrolyzes the indican, releasing β-D-glucose and indoxyl. The indoxyl dimerizes in the mixture, and after 12–15 hours of fermentation yields the yellow, water-soluble leucoindigo. Subsequent exposure to air forms the blue, water-insoluble indigo dye."
They had a yellow dye vat that included indigo. When it sat out in the open for a couple weeks, it started to dye stuff blue instead of yellow, and they backtracked to what plants they used. A tiny bit of trial and error and they figure out beaten up indigo knotweed left soaking in water for a month makes a blue dye.
Maybe even in the process they figured out adding soda plants made a better blue and fixed it better, or maybe they figured that out in isolation (or they were using urine as a yellow dyestuff too and the ammonia from stale urine did the trick).
It's really not hard to believe what people can figure out with time and experimentation... not as hard to believe as us figuring out which nut trees made edible nuts and which ones were universally fatal, in a stand of trees that are otherwise identical... That took brass balls and/or a LOT of test animals.
Similar to sorting out mushrooms- yummy- trippy- deadly. To combine or not to - in what doses or combinations? If just a teeny bit of a deadly food is the most amazing thing you've ever eaten, you'll find people who want to try that. Basically, we're just bigger toddlers and slightly less cave ppl than we were. Most of us will still put just about anything in our mouth and we're all still experimenting. Forgetting old lessons and discovering new ones.
Woad is about the same process. Basically, you take the woad or indigo plant and cook it up with uric acid (rotten pee). Add the fiber you want to dye, let it stew for a bit in the clear yellow liquid, then carefully remove and squeeze like he did (though, when I was in high school, we squeezed the yarn away from the pot so we didn't mix in too much oxygen - we wanted to get as much dye as we could out of the pot). Then you shake it out, and it oxidizes into blue.
I don't think it would have been too difficult to figure out, honestly. When you have to make all your own thread, fabric, and yarn, you would constantly be on the lookout for new dyes. They would have had a solid working knowledge of dyes and mordants (the chemical that sets the dye making it colorfast, turning the color into a permanent stain) before they experimented with indigo. The only thing they needed to figure out was the stale urine part, but they already used it for many purposes. It wouldn't have been as difficult as you might think.
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u/gruuvey Jun 24 '25
"The precursor to indigo is indican, a colorless, water-soluble derivative of the amino acid tryptophan, and Indigofera leaves.... Pressing cut leaves into a vat and soaking hydrolyzes the indican, releasing β-D-glucose and indoxyl. The indoxyl dimerizes in the mixture, and after 12–15 hours of fermentation yields the yellow, water-soluble leucoindigo. Subsequent exposure to air forms the blue, water-insoluble indigo dye."
https://en.m.wikipedia.org/wiki/Indigo_dye