Adventures in Indigo dying.

True Indigo: Indigofera tinctoria

Woad:  Isatis tinctoria

I've been playing with indigo again the last few weeks, getting ready to weave some viking fabric. I'm not an avid dyer. I'm more of a persistent dabbler. I am competent with acid dyes, and happy to use them if I can't get the color of fabric I want. I really enjoy natural dying, but haven't had as much time, or really the motivation to single mindedly investigate it. I tend to dye for a specific end result. I design a garment, research what colors it might have been in at that time and place in history, then find out what dyestuffs they were using in that time and culture, and try to use those if I can get them, and if they are reliable. There are some exceptions. Lichen dyes are not
sustainable, so  I tend to skip to something else for purple. I don't care to work with copper and tin salts with small children in the house, so prefer to use things I can mordant with iron and alum. Dying is one of the oldest crafts in existence, and if you don't care as much about replicating the method exactly, between finds of actual dye plants in archaeological contexts, and chemical testing of dyed cloth, there's a rich historical record. If you're dying to replicate something, it's fairly easy to pick materials, because there's thousands of years of preference to note which colors are light and wash fast, and which give the clearest, brightest colors. Of this historical dyes, indigo and woad are the only reliable source for good blues. As such they're a indispensable part of the natural dyers arsenal, but the process is kind of a lot of chemistry (and has a reputation for being finicky), which I think throws a lot of potential dyers off.

Most natural dyes form a chemical bond with the proteins in wool or silk either because the dystuff itself is rich in a substance that allows the color to bind to the protein (like the tannins in black walnuts), or by the intermediary intervention of a metal salt: alum, tin, copper, or iron. Indigo and Woad on the other hand make a mechanical bond with the fiber, which is why they work so well on cellulose fibers that many other dyes have trouble sticking to. You use a chemical process to shrink the dye molecule and force it out of suspension and into solution. Then you dip your material to be dyed. When you take it out, the oxygen reacts with the indigen, re enlarging the molecule and permanently tangling it in the fiber. The oxidation also turns the dye blue! The process is just really very different from other dye processes: from how you get the dye to a state where it will give a washfast color, to how you actually dye the material (no simmering here! the maximum that you dip the material is 5-10 minutes in a nearly exhausted pot. I've never gone more than five. You get darker colors by successive layers, not by longer processing.)

It's a little like magic really: You pull the skeins out of the dye bath looking like dirty yellow and as the dye drains off of them they turn brilliant blue. It makes me feel a little like an enchantress every time I do it!

Indigo and woad plants don't give up their color easily! You get the indigen out of the plant by a fermentation process. I don't do this part, because it's smelly, time consuming, and requires the ability to keep a big stinky vat at warm temperatures (so stinky that Queen Elizabeth banned the construction of woad dying within a certain radius of her residences). It's not impossible, but I'd rather save my time for something else, and buy the pre fermented powdered product. (Persistent Dabbler.) I've gotten this both from Dharma Trading (who also carries the chemicals you need, and provides great customer support if you run into trouble with your dye vat) and from The Yarn Tree, who sources theirs from a social enterprise in Bangledesh. The Yarn tree indigo didn't dissolve as completely (there were some gritty particles in the bottom of the dye bath), but did seem to give really good color.

This is the best reduction I've ever gotten. Probably it should
go a little more yellow, it's still got a tinge of green to it.
You can see the somewhat mettalic/blue slick on top of the
dye here. I've not completely gotten rid of that ever. I tend to
sort of sweep it off with a paper towel before dying.

 After you have your indigen extracted from your plant, or your powder mixed into your dye bath, you are not ready to dye. What you have is dye particles suspended  in water, what you NEED is dye particles in solution. Indigen is grumpy about going into solution. The process works best at a PH of about 10, which is usually achieved by the application of soda ash. I do this by weight, and then by watching the dye bath, but the clever well prepared dyer can also use ph test strips. Then you use Thioruea Dioxide, added a little bit at a time, with 15 minute waits between additions, to force the dye into solution. The process of forcing the dye into solution is called "reducing' the dye bath. When the dye bath is ready, it will be bright yellow or yellow green and translucent.

This all sounds like it should involve test tubes and lab coats and whatnot, but what it really means is mixing a teaspoon of Thiourea Dioxide into hot water in a mason jar. Bringing your dye bath up to 125-150 degrees F. Adding half the dissolved thiorea. Stirring GENTLY (because oxygen forces the dye back out of solution). Waiting fifteen minutes: checking the color of the dyebath, and repeating pretty much interminably. With or without supplementary and unflattering muttering about the dyepot and/or the life choices that led you to dye with indigo in the first place.

Once it finally reduces you can run test skeins (presoaked) to see how long you need to dip! Never more than 5 minutes in a fresh pot, if you leave it in too long the color won't tend to be wash fast but will "crack" and slough off, turning you blue every time you handle it. these little samples were 30 seconds, 1 minute, and 2 minutes. I ended up dying my first dip 3 minutes, and my second dip almost four, as the dye bath was starting to run down. You can REALLY see the blue oxidized skin over the dyebath here (this was foamy skin because I had let it get too close to boiling) I skim that off with a paper towel, because it's almost oily, and if you don't get rid of it, it coats the fibers on the way into the dyebath and they don't come into uniform contact  with the dye (learned THAT the hard way).

Then dye! It pays to be careful here, you want to stir as little as possible and allow as little dripping into the pot as possible. Basically anything that will introduce oxygen is to be avoided. I pull the skeins out, let them stream into the pot, with the tip of the skein basically touching the pot, then wring them out over a second pot, and hang them on a line to oxidize fully. When I'm totally done dying, I pour the oxidized dye from the pot I wrung the skeins into back into the indigo vat. I ALWAYS do the actual dying outside. (another thing I learned the hard way) because drips are basically unavoidable, particularly as you need to spread the wet skeins out to contact the oxygen, and the drips stain most things. (I'm typing with blue fingernails at the moment....) Also it smells like boiling rotting plants.

Spread out to oxidize! straight indigo, indigo overdyed over Weld, and the bright screaming yellow is weld. 

 Once your dye has oxidized it can be sent back in for another dip if you want darker results, or even a couple more dips. Then you have the normal post dye routine: rinse, wash with syntrhapol (I use the Dharma brand) to remove any un bonded dye (so your fabric doesn't turn you BLUE). then rinse till the water is clear, and I send it through the spin cycle to speed dying. A retayne soak can be used right after it comes off the pot, I've done it in the past. I didn't this time, I don't have enough data from using the dyed material to know if this is worth it yet.

Finished dye (mostly finished. I decided some of the indigo skeins were blotchy/lighter and sent them in for another dip. also that one noticeably yellow green skein got re-dipped)

Things I learned: you have to tie indigo skeins far more loosely than you do simmering type dyes. you're depending on rapid, even dye absorption into the fibers, and evidently ties that are loose enough for simmering dyes, are tight enough to leave light spots on indigo skeins.You can't throw the whole lot in at once like you can when you do simmering type dying. anything RESEMBLING crowding in the pot means that you get light spots. I ended up finding that two of these skeins at a time was just right. You don't want to stir in a way that folds in oxygen, but you do want to kind of, swish the skeins back and forth under the dye to make sure that the dye has penetrated the interior of the skeins. Keep some thiourea dioxide dissolved in water handy and watch the color of your dye bath if you're doing a lot of dying. if the color starts to go green? Add some thiorea, and wait ten minutes for it to settle. It's worth how much of a pain it is in consistency of color (the green means that dye is oxidizing and therefore becoming unavailable to bond with your fiber, so in addition to removing dye from the bath on the skeins, you're making some of it unavailable, so your vat start unexpectedly producing a much lighter shade.) . The good news is, even my blotchy skeins came out pretty well after another trip through the pot, so most problems are non fatal if you're erring on the side of light, rather than dark.


The best news is, once you've got your vat going once, it's more amicable to keeping going. you can store it in a sealed bucket, stir it every so often, and it will last for months! if it's getting light, add some more indigo powder mixed into water, and as it oxidizes you add more thiourea to reduce it.

This is just me fuddling through the process with the aid of the dharma dying tutorials, plus troubleshooting help from the dharma staff. there are entire books devoted to indigo dying (Dharma sells a couple that look interesting), and if you want to be more than a persistent dabbler, that's probably a good investment!