I planted out my Japanese indigo (Persicaria tinctoria) several weeks ago, having grown it all from seed. This week I picked some leaves and rubbed them on the page of my sketchbook to see if any blue appeared. It did (ignore the buff coloured stain to the left of the image, which is nothing to do with it). From this I knew that I could make a vat from the crop.
I began by picking half a bucketful and testing it as a small vat. I achieved a very good blue, which was used to overdue some cochineal-dyed scarves I had shibori-tied ready and waiting. You can see the result in the gallery below.
On the second vat I used a whole bucketful of leaves, rammed down hard. I just pick the tips, like tea: not the whole stalk. I sometimes weigh the leaves before processing but the material was wet after rain and there didn’t seem much point. I don’t always strip the leaves from stalks either, so a known dry weight is somewhat academic because the stalks don’t, as far as I know, produce any colouring matter.
On the day I dyed the second bucket I live-tweeted the various stages with images and received a good response. I think more and more people are trying to grow, and dye with, their own indigo.
With colleague Christina Chisholm I co-authored a piece on growing and using Japanese indigo for the Journal for Weavers, Spinners and Dyers in 2011. It was a free download and you can still access it here so I don’t have to write it all out again. We included some information on growing the plant in two distinct climates (Devon and north east Scotland). Christina has much more experience with dyeing wool, so fibre dyers might find her comments useful. If I were to be able to edit the article I’d make a couple of additions / amendments:
1. I have since found that I don’t always see a blue froth when I whisk up the strained dye bath. Instead, the sherry-coloured liquid darkens and looks greener – but the froth is often colourless. Why? No idea. These days I have stopped using soda crystals and use washing soda instead. Maybe that’s the reason.
2. I have found that leaves are often ready whether or not they have the red/blue tinge shown in the Journal download document. What I have heard since (but don’t know if it’s true) is that you need to use the leaves before the plant produces flowers.
3. I try to encourage flowers for seeds each year and there is some urgency about this as in the UK the plants die with the first big frost. I mark a few vigorous stalks early on by tying a conspicuous ribbon round each one. Then I can’t pick them by mistake. I let these stalks develop flowers as early as possible.