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Experiments in Natural Dyeing: Fresh Indigo (Polygonum tinctorium)


Japanese indigo leaves and flowers
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I've done a fair bit of indigo dyeing using the powdered, pre-reduced indigo and have always found it completely magical, and pretty simple to achieve beautiful results. This year, I asked my friends Glynis and Fraser of Aldergrove Farm to grow some fresh indigo for me, so I could try to take the process all the way back to the source (as well as use certified organic indigo). So, in late September, I picked up a big ol' bag of Japanese Indigo (Polygonum tinctorium) from them at the farmer's market and set to work.
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Japanese Indigo
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Below, I'll share the method I used to extract the indigo and make a dye vat (based on Jenny Dean's instructions in "Wild Color"), as well as several stumbling blocks I experienced along the way. That way, if you're trying it yourself, you can hopefully learn from my mistakes.

Step 1: Harvesting

Ok, I didn't actually do this myself (thank you Glynis), but you pretty much just cut the plant down. If you cut just above the second or third leaf node, the plant will keep growing and you'll be able to get multiple harvests. Once cut, the fresh leaves should be processed as soon as possible to maximize the amount of pigment.

Step 2: Prepping

It's only the leaves that contain the pigment so if you're tight for space in your dye pot, it's best to remove the leaves from the stems. This took me foreverrrrr, so I would recommend skipping this step if you can fit all the plant material in your pot.
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Stripping indigo leaves from stems
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In the end, I had 11 glorious lbs of fresh Japanese Indigo leaves to work with.

Step 3: Heating

Cover the leaves with water and heat slowly for 1 hour. Do not let the bath get bigger than 180! Too high a temperature can destroy the indigo!
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Extracting indigo pigment
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I will describe my mishaps more later, but I'm pretty sure that this is the step I didn't pay enough attention to. In the future, I would definitely use a thermometer, and stir the pot often to distribute the heat.

The vat is ready for the next step when it turns a rich sherry reddish brown.
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Strain and let cool to 120°C. (You can reserve the leaves for a second dye vat of pinky tans, supposedly, although I ended up with pale yellows and olives in my second vat.)

Step 4: Aerate

In all instructions I read, this step always sounded very easy. Pour the liquid from bucket to bucket to introduce oxygen. You can also whisk it by hand or with an electric beater.
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Once it makes contact with oxygen, the indoxyl (indigo precursor) turns to the insoluble indigotin (or indigo pigment). In theory, the foam that develops on top should turn from yellowy-green to blue and that's when you're in business! For me though, whisk as I might, I could not get the foam to turn blue. I still don't know the official explanation of this, but what I think happened (thanks to the detective work of Carolanne Graham, another Toronto dyer) was that I overheated the vat and destroyed a lot of the pigment. Because apparently it shouldn't take 2 hours of hand whisking and pouring or 4 hours of electric beating to achieve the blue foam. I did keep going, and was able to get some colour, so if you can't get a blue foam after 1/2 hour, move on to the next step- you should still have some success.

After this stage, you could leave that for a few days to allow the pigment to settle, and carefully remove the liquid in the top until you're left with just the reduced indigo.

If you're going to make the vat right away (which I think is the most efficient way to use all the indigo, especially for a small batch), continue on...

Step 5: pH and Deoxygenation

As I mentioned , indigo is not water soluble and therefore won't automatically adhere to the fibre if you dipped it in at this point.

To make it water soluble, it must be converted back into indoxyl by increasing the pH (aka make it alkaline, to between pH 9 and 10) and removing the oxygen.

There are a couple of methods for doing this. I used the first, since it's the fastest and it was already 3am when I got to this stage

1. Soda ash to increase pH; Thiourea dioxide to remove the oxygen

Pros: quick and efficient
Cons: can irritate, thiou dio r

2. Lyme to increase pH; Henna to remove o2

Pros: all plant and mineral based additives
Cons: not as efficient

3. Lyme or Soda ash to increase pH; Fermentation to remove o2

Pros: fewest inputs therefore lowest impact, fermentation is fun
Cons: takes up to 3 days to be ready, kinda stinky
Heat very gently for about 1 hour, until you see bubbles and a coppery sheen forming on top of the vat. The liquid should have turned a pale yellowy-green.
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Indigo vat
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Step 6: Dyeing
Ok go for it! pre-soak your fibres, then squeeze the excess moisture out. Dip them gently into the vat, being careful not to add in oxygen. Leave them in the vat for 5-10 minutes, remove careful, and let oxydize. This is the magical part- you'll see the fibres turn from an almost neon green to indigo blue right before your eyes!
Since you're working with fresh plant material, there may also be some green chlorophyl to wash out before you get to see your beautiful blues.
indigo dyed fabric oxidizing
Indigo dyed fabric
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Wash well, and enjoy your new blues!
The End. Thanks for reading!
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P.S. Feel free to get in touch if you're working with an indigo vat and run into a snag. I'd be happy to offer advice. info @ westlakeknits.ca
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P.P.S I'll be selling seeds and seedlings for Japanese Indigo plants in spring 2017! Stay tuned.
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