Dyeing with woad – Salt extraction method

Dyeing with woad – Salt extraction method

This year I've got into gardening in a big way, partially inspired by my wish to grow my own dye plants. I have an abundance of calendula and coreopsis, which will yield golden-yellow, green and maybe orange. I have a couple of madder plants that I'll eventually harvest for their roots, giving a lovely red. And back in spring, I sowed some woad seeds in the hope of growing my own blue dye. I opted for woad rather than the more potent indigo partially out of a bit of nostalgia for our British textiles history, and partially knowing that the plants do well in our climate.

Germination wasn't great, but the ones that did sprout, I planted out in the garden. The plants have been growing over the summer, only slightly held back by the slugs and caterpillars that are currently running rampant.

Woad in the garden

I've never dyed with woad or indigo before – both can be processed to produce indigotin, the valuable blue pigment that's so strongly associated with these plants. While I'd love to brew up a proper vat to extract those rich, deep blues, I definitely don't have enough plants growing for a big enough harvest to make it worthwhile. Preparing a vat takes multiple steps, chemicals that I don't have to hand, and a fair amount of time. But, inspired by Rebecca Desnos, I decided to try a less common method of extracting the pigment, using salt. 

Fresh woad leaves

I picked about half the leaves from each plant, resulting in 50 grams of fresh leaves. That's convenient because my wool yarn is in 50 gram skeins, and I use 1:1 as a ratio of dyestuff to fibre when trying out new dye material. It's usually a good starting point, and I use the results to inform the quantities I use for future batches. 

I washed the leaves and, in a stainless steel bowl (which is non-reactive so won't affect the dye colour), tore them into small pieces. In the meantime I put a couple of skeins in an alum and cream of tartar mordant bath to simmer while I prepared the woad. 

Torn woad leaves

I sprinkled some salt over the torn leaves – I wish I could tell you how much salt, but I eyeballed it. I'm terrible like that. Maybe you can see from the photo roughly the amount I used.

Woad leaves sprinkled with salt

Next is the fun bit. The salt draws moisture out of the leaves – much like preparing vegetables like aubergine and courgette to avoid sogginess when cooking. In order to extract as much water – and colour – out of the leaves, you need to squish them up. 

Squeezing pigment out of woad leaves

On first contact with the salt a small amount of green liquid started seeping out of the leaves, and squishing with my hands drew out loads of deep green juice. There's something immensely satisfying about the process of squeezing and crushing the leaves, foamy green dye oozing out between your fingers, leaving little clumps of wilted leaves. 

Once I was satisfied that not much more pigment was coming out of the leaves, it was times to add the damp, mordanted yarn. I used my Mendip 4-Ply in Sheep (Sunny).

Mordanted yarn ready for dyeing

I put the yarn in the bowl, trying to maximise contact between the dye liquid and the wool. Breaking up the clumps of leaves and pressing them into the yarn, kneading the pigment into the skein while taking care to avoid tangles, was good fun.

Wool yarn with fresh woad pigment

At this stage things are all still decidedly green in colour, bright and fresh. I was looking out for a colour change, ultimately expecting a colour in the turquoise–teal range. I wasn't expecting a very strong colour, as the amounts of dye in woad are a lot less concentrated than in indigo.

Green pigment from woad on yarn

As I kept squeezing and turning the yarn to try and get even coverage, it did seem that the colour was shifting very slightly. The leaves dried up after a while, so I removed the yarn and added a little more salt in the hope of extracting a little more colour. 

Adding more salt to woad leaves

After some more kneading of the leaf scraps, it seemed to work! I was able to get a bit more moisture out, which helped even out and strengthen the colour on the yarn. 

Woad pigment turning turquoise on wool

As the colour was exposed to oxygen it definitely started turning a bit more teal. Once I got about as much coverage as I thought I was going to get, I decided to fix the colour with some heat. This may not be necessary, but I tend to be a bit belt-and-braces about these things. I wrapped up the skein loosely in a compostable carrier bag and put it in the microwave for a minute. 

Turquoise yarn after heating woad dye

On unwrapping the skein, the colour change was immediately noticeable, as was a strong smell. Woad is a brassica, much like cabbage, broccoli and kale. You can probably imagine it! Now that the dyeing process was finished, I hung the yarn up to dry. Usually I'd let the yarn sit in the dye bath until the water is completely cold, but as there wasn't a typical dye bath here, I decided to let the skein dry completely, and rinse it a couple of days later. 

I had heard that woad, prepared using a standard method for natural dyes, can yield pinky-apricot colours. Not entirely optimistically, I boiled up some water to pour over the seemingly spent woad leaves, thinking I didn't have much to lose if nothing happened. 

Boiling water on spent woad leaves

An eerie blue tinge was evident, looking like copper sulphate, which was encouraging that there was at least still a little pigment left in the leaves. I added this to a pan with warm water and a fresh mordanted skein of the same wool yarn. Leaving the pan on low heat, I really didn't expect much – maybe there was a slight yellowy tinge appearing. Then returning a while later I was amazed to find the peachy tones I had read about! 

Second dye bath using woad, giving peachy tones

I left the yarn to cool overnight before rinsing both skeins. Both colours became a little paler, which I expected, but there was very little colour run-off into the water and the resulting shades are quite lovely. 

Woad dyed wool yarn skeins

 As a not-at-all-experienced dye plant grower, I can definitely say that woad has earned its place in my garden. The blue tones are rare and invaluable – and to be able to use the spent leaves for a completely different colour is a massive bonus! I'll be sowing a lot more seeds next year and have an area dedicated to woad, and hopefully then I'll have enough to harvest for a real vat to aim for those deep blues! 

 For more yarn and craft related projects, consider subscribing on Patreon where I post a making video every month. If you enjoyed this post, you can buy me a coffee on Ko-fi as a thank-you. 

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