Tag Archives: dyeing

Woad Fermentation Vat No. One: Day Seven.

In fact a summary of days 2–7. In pictures and words. I really, REALLY wish I could share the smell as well, as I think that’s significant, but I daresay many of you wouldn’t enjoy the, er, pungency. It’s living in my office/spare bedroom, and I’m just hoping the smell won’t linger once the vat is finished. I had intended to keep it in the garage, but it wouldn’t be fair to inflict it on my husband.

According to the thermometer on the vat the brewing belt is running slightly hot, I think, nearer 28 than 23°C, so I’ve wedged a pencil between the belt and the vat to reduce the heat input.

pH papers from vat testing over the week:


The vat on Day Three, 12 May. pH 8-9
The organic matter is waterlogged and has sunk to the bottom. There are a few bubbles, some patches of scum, the vat smells of rotting vegetation. The pH is low (acid): I sprinkled 1/2tsp of garden lime on the surface and stirred it briefly and gently.


Over the next three days the vat liquid became darker, the smell of rotting vegetation intensified, the greyish scum became thicker. Daily pH tests gave readings of 7–9, lowered by the acids produced by the rotting woad and bran; I sprinkled another 1/2 tsp of lime on the vat on Days 3–7. When in doubt, go alkaline as indigo will not convert to the soluble form in an acid environment. The smell became more complex. I can’t think of a good way to describe it, but no longer ordinary rotting vegetation. Richer, darker.

Day Seven. I suspect fermentation has peaked, as after yesterday’s lime the pH remains high – it’s well over 9, the maximum on my packet scale. The vat liquid is dark, there are now scattered patches of a thin shiny, almost metallic scum on the surface. The smell is richer, more complex, and not particularly pleasant (I much prefer the odour of a fermenting urine vat!).


The combination of changed odour and high pH made me think it might be worth testing for blue: the strings are tied to some scraps of scoured muslin that I’ll leave in overnight, and for multiples of 12 hours. I have a strong suspicion that 100g of woad leaves won’t produce a strong blue in any case.


Woad Fermentation Vat No. One, Day One.

So it begins. Over the last couple of days I’ve been assembling and collating information about indigo, woad, and fermentation vats. I’ll post a summary in due course; today I started my first woad vat using my first ‘best guess’ for a process based on my reading. It’s largely based on the instructions for a woad vat in Liles’ The Art and Craft of Natural Dyeing, but without the addition of indigo powder: I want to see what blue I get from 100g of woad ball before I add indigo. I aimed for the pH levels described by Dorothy Miller in Indigo, from seed to dye.

In Indigo Jenny Balfour-Jones describes the couching of woad balls. According to her sources, when the process is complete good woad is dry and mouldy, a condition known as “well beavered”. Mine wasn’t completely dry (I’d left it covered), but it was covered by a remarkable fine grey-white mould. The entire couching process seems to have taken place very quickly, perhaps because I used rainwater rather than tap water to avoid chlorine and other inhibitors of bacterial growth: on 7 May I crushed 100g of woad ball, moistened it with rainwater, and set it next to my desk so I could see what happened. I kept a lid on the dish to retain moisture. It heated up within hours; I turned it on the 8th and again on the 9th, by which time it was cool.


I assembled my kit. The white bin holds 25l/6 gallons; the black strip on it is a liquid crystal thermometer, and the orange thing is a ‘brewer’s belt’ that should maintain a good fermentation temperature, somewhere between 22-28°C. I plan to put that coil of plastic mesh or something similar at the bottom of the vat to keep cloth and fibre away from the fermentation debris.


Liles gives quantities for 6-8 gallons; I halved them for a 3 gallon/12.5 litre vat to begin with, and used washing soda rather than lye as an alkali. I dissolved 0.5oz washing soda in 1 litre hot boiled tapwater (boiling should drive off the chlorine), added 0.5oz wheat bran (slow release carbohydrates to fuel fermentation) and 0.5oz madder root (traditionally added because the bacteria on the roots kickstart the fermentation process). I left this to soak for an hour to hydrate the bran before pouring it into the bin and adding 8 litres of rainwater (total 9 litres). I boiled 2 litres of tapwater, added 1.5 litres of rainwater, and brought the entire volume to 70°C on the stove: woad contains both indican, the precursor for indigo blue, and isatan B, a related compound that will create blue, but which according to Balfour-Paul requires a higher temperature at the start of the fermentation process followed by rapid cooling.

I scraped the couched woad into the hot water, stirred it thoroughly for 5 minutes, then dumped it into the vat solution to cool it rapidly.


Maintaining the correct pH range is critical for a healthy fermentation vat, and the dyeing process. If fermentation is too enthusiastic, lactic and other acids will drop the pH to the point that the vat will not dye. The acidity must be countered by an alkali, but if the pH is too high fermentation will cease and the vat will damage protein fibres. A pH of c. 10 appears to be good for both fermentation and dyeing, although the woad vat should operate down to pH 8. I decided to aim for pH10 in the vat before fermentation starts. According to my pH meter I was bang on. Remarkable! I therefore omitted the 1/2 tsp lime called for by Liles’ recipe; it may be that our rather alkaline tapwater (pH 8.4) rendered it unnecessary.

I bought pH paper – litmus paper – to check the pH of my fermentation vats a couple of years ago, but neglected to check that the range was appropriate. Mine are intended to check the pH of body fluids (don’t ask, I don’t know and I don’t want to know) and the chart only goes to pH 9 whereas for these vats you’ll need them to go all the way to 11. However it seems that the paper will indicate the higher readings, I just have to create my own calibration records based on the pH meter. Note that the pH 10 paper is in fact more blue-green than it appears. The very blue paper on the right was the 1 litre initial stock solution, which had a pH of 11.2.


One thing is very clear from my reading: a good working fermentation vat is as much a matter of luck as judgement. Japanese indigo artisans pray to Aizen Shin, the god of Ai (indigo) for success. I shall drink a toast to Ai tonight, just in case.

I’ve started preparing for the next vat, too. Guess what that will be based on?


2015: A Summer of Blue

Or so I hope.

I’ve had a thing about indigo for longer than I care to remember. I think it started when my mother included indigo vats in a summer school dyeing class she taught in the early 1970s; in my mind’s eye I still see the shimmering metallic blue-copper-purple surface of the liquid and the cloth emerging from the vat green, turning deep indigo blue as I watched. Some years ago I started to recreate the magic. I began with the simplest chemical ‘colour run remover’ (I’ll explain these terms later) vat, and managed to dye some spinning fibre blue. I felted it too, but still: blue! I read of traditional fermentation vats and HAD to try to establish a sig vat based on the bacterial breakdown of urine. I briefly managed to get it working and saw a different blue, murkier and darker, on wool that 4 years later still retains the faint barnyard odour that for centuries indicated the finest blues.


In 2013 my first attempt to grow Japanese indigo failed to thrive outside in a typical British summer, but I discovered that woad – the traditional blue of northern Europe – thrived. I wrote a blog post “Blue! From leaves!” about the fun I had crushing the leaves and extracting the indigo to dye blue, then using the ‘waste’ leaf matter to dye a second completely different colour known as woad pink.

The fabulous gift from A. of John Marshall’s new book on working with fresh indigo has inspired me to plan greater efforts this summer. Woad and the various plants known as ‘indigo’ that grow in warmer climates all contain the same compound – indigotin – that produces indigo blue, but woad contains less than most other indigos.

The summer of blue

I’ve made careful preparations. I want to try some of the interesting techniques that John describes; to be sure of them, I need fresh tadeai, the Japanese indigo Polygonum or Persicaria tinctoria. It won’t thrive in our semi-continental climate and clay soils; it requires a warmer maritime climate, higher humidity and reliable summer heat, and moist soil rich in organic matter. So I’ve bought a tiny greenhouse, the appropriate size for our tiny garden, complete with raised bed that I’ve filled with compost and leaf mould. I’m hoping this will allow me some control over heat and humidity.


I sowed the tadeai seed that John Marshall kindly included with the book indoors in April, keeping the seed tray in the warmth upstairs next to my computer. I even repurposed my drawing desk light with a grow light bulb. And I’ve had some success! Now the tadeai seedling are hardening off in the greenhouse, and seem to be thriving.


In theory woad leaves could be used for the same techniques, although the colours might be fainter.  I need more woad! Sadly my first woad sowing either failed to germinate or, equally possible, the seedlings were eliminated by the horde of slugs and snails that reside in the garden. To the far left of the greenhouse there are three rows of woad re-sown a week ago, and I’m about to go outside to apply slug pellets and cover them to protect the birds and other animals.

Fortunately there are other sources of woad in the UK. The Woad Centre in Norfolk has been growing and harvesting it for some years. They sell indigo pigment extracted from the leaves and a variety of other products, but I am most interested in their woad balls. For centuries woad was a valuable commercial crop, preserved and transported to dyers in the form of balls formed from the chopped and kneaded fresh leaves, then left to dry. The balls can be reconsitituted for various forms of indigo vat, including the same extraction process I used in 2013. I’m now more interested in the various forms of fermentation vats, and have begun to prepare for my first attempt by ‘couching’ 100g of woad ball. This entails crushing the balls as finely as possible, moistening the mass, and leaving it to rot down/ferment into a dark green-black mass which is then used in the dye vat. I haven’t yet come across any explanation of the reason for the couching process; my guess is that the fermentation breaks down cell walls to ensure more of the indigotin compound is available to the dyeing process.

WoadBallPrepThe crushed woad ball in that dish were prepared and wetted with rainwater two days ago and I’m very happy: the mass is darker and warm to the touch. It’s working! It has a strong odour, the smell from the centre of a pile of grass clippings, and that seems right.

I have three 25litre plastic fermentation bins waiting in the garage, along with 2kg wheat bran (I can’t find rice bran) to fuel further fermentation, a pH meter, LCD thermometer strips and a ‘brewing belt’ heater to warm the vats if the British summer fails again. I have commercial natural indigo to add more pigment for a deeper blue. I am almost ready… I just have to set up a, er, urine donation facility next to the toilet :-)

Blue! from Leaves!!!

The Hat has been my main focus for the last few months and I can’t blog about it because I hope it will be published. Sorry …
But I can tell you all about another chapter in My Adventures with Indigo. It’s a long one; you might want to make a cup of your favourite beverage now, before you start. 

About 12 months ago I ordered both Japanese Indigo and Woad seeds, my cunning plan being to throw cabbages to the wind and grow blue instead. Alas, I have no greenhouse: the bitterly cold winter and late, wet spring put paid to the Japanese Indigo, which even indoors scarcely showed a leaf before giving up the ghost. This isn’t the climate it was looking for. Woad, on the other hand, was and still is grown here as a crop, so I expected more of it. To its credit, it delivered. Woad is apparently a gross feeder, in this case meaning that it needs nutrients and lots of them, rather than having no table manners. I fed it regularly with blood, fish and bone, and watered regularly in dry weather. It’s biennial; the first year leaves give colour, the second year there is no colour (can’t vouch for this yet), but you get seeds to grow more. Harvest the leaves from midsummer on. This post depicts events on July 21, my first pick.

I have both Jenny Dean’s Wild Colour (I have an earlier edition) and Rita Buchanan’s A Dyer’s Garden, both of which give instructions for dying with fresh woad leaves. It’s extremely straightforward. 

First grow your woad. I suspect it’s important to move as quickly as possible from harvest to hot water, so I set up my kit next to the woad, which is the lowish, bright green, elongated leaves to the right of the cabbages. The net is essential: everything under the net is extremely dangerous is food for the caterpillars of Cabbage White butterflies. If you don’t prevent the adults from laying eggs on the leaves, you will have no leaves. Ignore our bike gear, it’s just drying out/absorbing UV to kill bacteria.

Basic equipment for an afternoon of fun: well-wetted materials to be dyed blue, plus a large container (I used a jar because I can see the colour of the liquid in it), a large wooden spoon, rubber gloves, a glug or two of household ammonia, a BIG saucepan or stockpot (it will hold only water), with trivet and a thermometer accurate from 0–100°C. For further excitement you’ll need a saucepan you don’t use for food, and 1 tsp of alum mordant. Read the instructions below to make sure you understand what you’ll be doing and why.

Fill the kettle (really full) and put it on for tea. 
Pick the leaves as quickly as possible, and stuff them into a container. A large glass jar is good because you can see the fluid change colour, which is helpful. No need to shred them finely or anything, I just grabbed handfuls, slugs and all, ripped them in half and stuffed them into that large jar. 
The kettle should be boiling by the time you finish: pour the boiling water into the jar, enough to cover the leaves. Make tea with the leftover, if you want any; I opted for squash instead. Leave the leaves to soak. 

If you plan to go straight to dyeing once you’ve got the indigo from the leaves, at this point you should half-fill a saucepan or stockpot large enough to hold your jar with water at least halfway up the sides, put the trivet in the bottom (to prevent the glass jar from overheating on the metal) and put it on low heat (you’re aiming for 100-120°F (38-48°C). If you haven’t got a trivet, I use a layer of metal table forks.

The jar of leaves soaking in hot water.
The fluid will change from water-clear to dark sherry-brown as the leaves wilt. After an hour, remove the leaves (I used a kitchen strainer), squeezing out every drop of fluid, and put them carefully to one side. You will use them again.
The chemistry of indigo dyeing is not complicated, but it’s important. The dark brown fluid in the jar contains indigo from the woad leaves in the form of indoxyl (more detailed info on Wikepedia, scroll down to Extraction). To extract the indigo from the fluid, add a glug (about 1 tablespoon for this jar) of household ammonia to the fluid. Buchanan says baking soda will also work, I haven’t tried it.). Now pour the fluid back and forth between two containers, exposing it to the air as much as possible. You want bubbles and lots of them!
The foam starts yellow but turns a beautiful turquoise as the fluid is oxygenated, transforming the indoxyl into insoluble blue indigo. Once it’s as blue as blue can be, it’s decision time. You can dye with the fluid and indigo, or you can filter out the indigo particles and save them for another day. Filtering takes longer to do but much less time to describe, so I’ll show you that first. If you want to DYE NOW! skip the next section.

Filtering the indigo particles
My reading suggested that coffee filters and such aren’t fine enough to trap the bulk of the indigo particles. Some people use proper filter paper, but I didn’t have any. Instead I used two layers of extremely finely-woven commercial silk fabric to line a small tea strainer. Straining a smaller volume (I did this with the second batch of woad processed in August) took the best part of two days. Save the filtrate (the filtered fluid): it probably still contains enough indigo to dye something else blue if you follow the instructions for dyeing with the fresh indigo solution, below.


I suspect that’s very impure; there’s probably a lot of vegetable debris as well, but I see no reason for it not to work. 

I dyed a skein of cotton with the fluid that ran through the silk. A paler blue, but still blue!

Dyeing with the fresh indigo solution
If you decide to go ahead and dye with the solution, from this point the process is similar to a standard chemical indigo vat. Make a solution of reducing agent (thiourea or Spectralite), 1 tbsp in a jar of warm water and add it to the fluid in the jar. The reducing agent absorbs oxygen in the water, which transforms the insoluble blue indigo particles to the yellowish soluble form. In this form they are absorbed by the materials you want dyed. Now, given that you’re trying to REMOVE all the oxygen from the solution, once you’ve added the reducing agent you should take great care not to ADD oxygen (air!) unnecessarily. Stir gently, don’t create bubbles. To activate it, the solution must now be heated to 100-120°F (38-48°C) for about an hour. Check the temperature of your water bath and adjust it by adding boiling water or cold water as needed. Put the jar in. Stir it gently from time to time and check the colour of the fluid. It should become yellowish: with luck you can see that the bottom of the bubbles and the fluid is in fact yellowish.

When it looks like that it’s ready to use. Take the jar off the heat if it’s more convenient. Squeeze excess water from whatever it is you’re dyeing and add it to the jar.

Note the bluish tinge to the merino locks, which still contained some air. A hint of what is to come. I left the fibre and yarns (wool and silk) in the jar for about 15 minutes. When removed from the jar oxygen hits the pale green-yellow liquid: it begins to turn blue. First turquoise, then darkening further. 

You can dye more material in the jar until the indigo is exhausted, but remember that each batch adds oxygen. If the fluid becomes more blue than yellow, add more thiourea or Spectralite and repeat the heating process to drive off the excess oxygen, thus reducing the indigo to the soluble yellowish form that dyes.

Different fibres take and hold indigo differently: unlike ‘chemical’ dyes, in which the dye molecules chemically bond to the material, the soluble yellow indigo penetrates into microscopic cracks and crevices where, with luck, the insoluble blue particles are trapped, wedged firm. Those that aren’t trapped firmly will come off on your skin (and everything else) as the indigo blue ‘fades’ over time. Silk and other very smooth fibres have fewer places to trap indigo, so tend to end up paler than wool or cotton. But when they first come out of the vat, everything is simply glorious blue. In this case, glorious blue FROM LEAVES!!!

Well, not quite everything. That pinkish-brown skein of silk is just as magical, or even more. Remember I told you to save the leaves strained from the initial solution? 

Dyeing with indirubin: Woad ‘pink’
If you now treat the woad leaves from which the indigo was extracted as if they were standard fresh plant material, they will yield a totally different colour: woad pink. Mine was more brown than pink, but still absolutely astonishing to get two such different colours from a single leaf. The technique is simple: stir the strained leaves into a pan of water (I used rainwater, in case our very hard water affected the chemistry) and simmer for an hour or so.

Strain off the leaves – this time you can discard them! – and add 1tsp of alum mordant to the dye solution.

Add the material to be dyed and simmer for another 15 minutes or so, then allow the solution to cool with the material in it – leave it overnight if you can – as this yields a deeper colour. Here’s a closer view of the silk to show the indirubin colour: