Medieval woad vat - experiment with fermentation

Today a bit about woad fermentation vat. 
Woad (Isatis tinctoria) was one of the most popular dyeing plants in Medieval Europe. It is one of these weird plants which requires more preparations than just dumping in the pot of hot water. I will skip the bit of explanation with chemical formulas (not very comfy with them myself :P), but the main idea is to create a solution which would remove the oxygen (and thus make the blue pigment, indigo, soluble). Nowadays this effect is achieved mostly by adding some chemicals (e.g. a spectralite). I have dreamt though about replication the other solution: the fermentation vat. And finally managed this Spring!


From all methods of dyeing with woad, fermentation vat is the most demanding, but also (at least for me) the most satisfying, as it is the closest to an original medieval way.

There are different recipes from all over the world what to put into your vat for fermentation. I decided to stick to the combination most popular in European Medieval: bran and madder (I have replaced bran with oat porridge though, as I did not have any in hand when making the vat!). As a source of woad, I have used woad balls prepared last summer (you can read more about them in this note).

Proper alkalinity is the key when maintaining vat, and I decided to used soda ash for this purpose (next time I am going to prepare some ash lye, as originally used in Medieval Europe). Originally the woad dyeing was most likely performed in big stave vessels (imagine very big old-type barrel cut in half). Not having any of them, I have decided to use my replica of Early Medieval pottery.

I started from crushing woad balls with a mallet. Then I soaked ingredients overnight, and the next day put them into the vat with enough of soda ash to receive initial pH of 9 - 10.



The first challenge was providing the proper temperature. There are a lot of ways how it could be achieved in Medieval. From the middle and late Medieval, when dyeing was a regular occupation and dyers got nicely equipped workshops, they could warm up vat on the furnace, or (more likely in the case of woad), gradually add hot water to keep temperature (look below at this depiction of 15th century dyer from Nürnberger Zwölfbrüderbücher, and the illustrations from Medieval manuscript depicting dyers workshop).


In earlier times dyeing was a household occupation, and workshops were probably just simple sheds outside of the main house. Not having fancy utensils, dyers probably were more creative (I suppose they were used hot water, but also some kind of insulation).

I tried different combination (wrapping in the sheep fleece, hot water bottles, etc.) but finally, I gave up being Medieval and have just put my pot on the radiator (I have one of these old wide ones).


The first sign of SOMETHING going on was the rapid drop of the pH (the alkali needs to be constantly added to maintain pH around 9). Next, the bubbles appeared. Also, the vat has changed appearance. On the photos you can see how nice looking it was at the beginning, almost like some kind of exotic dish.


Well, it was just at the beginning: later it became muddy, yellow-greenish, and, most of all, STINKY. I have less than delicate nostrils, but this smell was overwhelming even for me (imagine a rotten cabbage with a hint of ammonia). No surprise that woad dyers were not welcomed in Medieval villages!


But, the most important, it worked. I needed a lot of patience, as the first results were not impressing - muddy shades of grey. But in the fourth day, something changed and threads started to come out of vat in shades of turquoise (still with a bit of grey, though).


The vat is an 'alive'. Recipe for the woad dying written in 15th century Italy states:
For the woad vat is like a man, that wants to eat and drink, otherwise, he dies; and so does the colour in the vat, that would vanish into fumes if it was not refreshed when needs it.
(quoted after J. Edmonds, Medieval Textile Dyeing).

And this is very big true. My vat one day got exhausted and, instead of blue, I took out the pale pink yarn! (the explanation is, that apart from indigo, woad plants contains also other colourants, which can influence the colour). But everything was back to normal when I 'fed' it with more bran, woad balls and madder.

I kept vat going for a couple of days, receiving a range of greyish blues. Not the best of my blues, but still blues: I was clearly on the right path. On the photos you can see the whole range of colours from my vat.


Properly maintained woad vat can be active for long weeks, but I needed to interrupt my experiment due to simple reason: the stink mentioned above...
(did I mention that I kept vat in the warmest place in the house: bedroom? My boyfriend is a saint!).
I moved vat outside, to the garden. I probably will try to reanimate it later, during long, summer days, this time with fresh woad leaves.
Cannot wait, as this is one of the most exciting experiments which I performed so far. Yes, even considering the smell!

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