Although I had my first dyeing experiments a long time ago, I’ve never tried dyeing with indigo. Indigo is produced by several different plants, and historically the important one here in Europe was woad (Isatis tinctoria). As the blue pigment in the plant is not water-soluble, the processing it requires is different from the normal natural dyeing process (which is pretty straight-forward and not that different from cooking). Turning the indigo pigment into a format that can be used in dyeing has always seemed a bit complex to me, I’ve always thought it is definitely something for later when I’ve mastered the “normal” dyeing process.
But as I have been growing woad this year, I knew sooner or later I need to learn the method. Growing woad has been reasonably easy although the start wasn’t entirely successful: I first sowed some seeds in self-watering modular trays in my unheated greenhouse, but only four seeds germinated. But I then sowed some more straight into a raised bed outside, around May time, and this worked much better as I soon had nice little rows of woad seedlings growing.
During the summer they have been very trouble-free. I have watered them at particularly hot spells (which there haven’t been that many this summer here in the UK), but that’s about it. I thinned the rows late June/early July time and planted some of the thinnings in plastic pots and they too started growing well. Although I wasn’t sure if the leaves had any blue in them so early in the season, I also put some of the thinnings in plastic bags and stuck them in the freezer, to be used later when I have more leaves (I just couldn’t bear to throw them away).
Yesterday I decided that the time was right for the first proper harvest of woad leaves. I picked the leaves, there were about 700g of them, and then consulted Jenny Dean’s Wild Colour to see what to do next. It did not seem too difficult: shred the leaves, pour boiling water from the kettle on them, leave for an hour. A nice easy start to the process, perhaps it won’t be so complex after all?
After an hour, when the temperature has cooled to 50 degrees C, strain the leaves (putting them aside for using later), add some washing soda until the sherry-coloured liquid turns greeny brown. Ok, again not too difficult, except that both of my thermometers had broken so I had to guestimate the temperature (without sticking my hand into the very dark coloured liquid). Unfortunately Jenny Dean does not mention how much washing soda you should use, but after I had added about 3 teaspoons I thought the colour could be described as greeny brown.
Then, to extract the blue pigment from the woad tea, you’ve got to introduce air to the liquid by whisking it or pouring it from one pot into another until the froth turns blue. Well this is the exciting bit in the process, I thought, I’m looking forward to that! And so I started whisking.
Whisk, whisk, whisk…. nothing happening… whisk whisk whisk a bit more, the froth is still distinctly green. Consulted the book again. Jenny says if the colour doesn’t change, then add a bit more washing soda and keep whisking, so added a bit more soda and whisked some more…. still no colour change so decided to change the method. So started pouring the liquid from one pot into another until my back started aching… and still the liquid was green (although my white bucket had turned slightly blue, which was rather hopeful). And so I kept on going for about 40 minutes until I had lost count of how much soda I had added (the pH was about 11 by this time, so very very alkaline) and still the liquid was very much dark green, not blue.
In the end, after no sign of blue except in the plastic wall of the bucket, I decided to give up and go back to the house to consult the internet to see what I might be doing wrong.
Having read the very useful instructions on the Woad.org.uk site (yes I do admit I should have done my research a bit earlier), I started wondering if my water had been too hot when I started adding the washing soda, apparently the pigment gets destroyed if the temperature is higher than 60 degrees. But of course it was too late to do anything about that now (I suppose I really must get another thermometer soon).
This site also tells you to let the indigo pigment settle at the bottom of your container in order to collect it for drying. It hadn’t been my intention to dry out the pigment, but I thought I might just as well let the green liquid settle and see what happens. So I poured the liquid into glass jars and left them for the night.
But I am now thinking perhaps I don’t have enough blue there to do any actual dyeing just yet, so I’ve decided to keep the liquid I’ve gathered so far (in this form it keeps for several months or even a year) and wait for the second harvest of leaves. Meanwhile, I am going to feed the plants with some high nitrogen fertiliser (apparently woad is a hungry plant and well fed plants produce more blue).
And the leftover leaves from the extraction process can be used to dye fibers in the conventional way to get some pinky tans (no mordanting is necessary), so that’ll be my next step while I wait for my woad plants to produce more leaves.