The Indoor Fermentation Vat


This is my indoor indigo fermentation vat. It lives in my room in a tall glass pasta jar with a screw cap. Thanks to the firmly closed top it doesn't smell unless you open it (and then not unless you stand over it).

After the year I've had this vat I'm still far from understanding it completely but it's given me many lovely blues nevertheless. I'm going to write down some observations in the hope that they may be useful to someone. I don't feel I know enough to give instructions but hope that my experience may inspire others to experiment in their own way.

As I understand it, a fermentation vat has two main elements the dyer can control - something to fuel the fermentation (bran, madder but it can be chopped dates, syrup or other sugary things) and a source of alkalinity (soda ash or wood ash lye etc.) which is necessary to dissolve the reduced indigo but also keeps the fermentation in check. The two elements have to be in balance. Too much fermentation and the vat goes sour spoiling the dye. Too much alkalinity and the fermentation stops and the dye doesn't work either.

My vat was set up with water, ground madder root, wheat bran, soda ash and powdered natural indigo.

When the vat is healthy the smell is quite sharp and ammonia-like. When it smells sweet-ish or 'flat' I add soda ash. At its best the liquid seems sort of thick and heavy, no blue bits float in it when I rub it between the fingers and bubbles slowly rise to the surface when I dip the fabric. If the liquid appears 'thin' and it doesn't dye well, I add some wheat bran boiled in water and let it ferment (adding soda ash as required so that the fermentation doesn't 'run away') until it appears right (that can take a week). Even at its best this vat never had the typical 'flower' (foam) on the surface and never looked entirely green. It can sometimes have the coppery sheen and be a little green around the edge of the jar.

I find that even indoors the temperature here is too low for the vat to work without additional warming. When I want to dye I close the vat in an improvised haybox (a cardboard box insulated with old towels) together with a freshly filled hot water bottle. The bottle keeps it warm for about 12 hours. When I'm not using it I leave it at room temperature.

During the year I've added about 25 g of indigo two or three times. I think my initial mistake was to use far too little - that's why everything came out looking pale.

The shape of the jar is perfect for dyeing my small silk pieces which can be suspended without touching the sediment on the bottom. I usually soak the fabric in water for at least an hour and then dip it in the vat overnight. Let the vat rest and the fabric oxidise during the day, followed by another dip the next night etc.


Here's a record of the deepening colour on a piece of cotton. I've added to it since here. Not much fabric is left and I still haven't reached the typical indigo blue-black that I'd love to see.

Do you have a fermentation vat? Are you going to try? Please let me know in the comments.


Sandie said...

I did once grow some Woad with the idea of doing some dye work but, never got around to it!

Sandie xx

Sea Angels said...

fabulous I must have a try at this..your colours are totally gorgeous xx

Margie Oomen said...

this long weekend i am going to set up an outdoor vat for indigo and one for woad similar to what you describe.
After reading this i might also try a tall mini vat for indoors as well and keep it in the kitchen.
I wonder if you put your indigo in a small pouch like others describe and gently squeeze it daily until it all dissolves or whether you have ever used methylated spirits to help dissolve the powder.

jo said...

thanks for this Eva, I would love to have a try working with indigo at home (as opposed to at workshops)and your comments spur me on to do something other than think about it!

DK said...

I've not considered doing a 'mini' vat before. The thought of having to keep a large tub of it in the backyard hadn't really appealed to me since I tried keeping a bucket of walnuts fermenting like that so I could continue to use them for dying and it was kind of a smelly pain to move around all the time for the regular cleaning and yardwork.

Lari Washburn said...

really fascinating.

julie schmulie said...

i did this type of vat once years ago, and had it going for a little while. but had a similar problem to you that it was hard to keep warm enough (same problem i've had with my zinc-lime vat). i used to periodically warm my vat using an electric blanket, but i like your haybox idea. i have a tendency to make huge vats, which are even harder to keep warm - you've inspired me to try making a smaller, more manageable one.

nicole said...

Thank you Eva for this. I've long wanted to have my own woad or indigo vat. This sounds very doable and exciting.

jude said...

i am going to try. i like the neat look of yours.

Eva said...

Sandie - I'd like to try a woad vat too. Some time...

Sea Angels - thank you x

Margie - I grind the indigo in a mortar, make it into a paste with some water and add that directly to the vat. I stir the vat quite often.

Jo - I'd love to try indigo dyeing in a workshop :) To see how others work with it. People seem to get dark blues so effortlessly in workshops.

DK - I started with buckets too but it was just too much mess to manage in a flat. I like doing all dyeing in miniature so a mini vat seemed the perfect solution :)

Lari - glad you find it interesting

Julie - I was wondering about the electric blanket but was afraid to leave it on for a long time. The only problem with the haybox is that the temperature is not constant but goes from quite hot to lukewarm (or cold if I forget to change the bottle). I wonder how much it matters...

Nicole - it is doable! It took me a while to connect all the advice I was reading in books and online to what I'm seeing in the vat but it worked out in the end.

Jude - good luck! mind you, it can get messy even with the neat jar (I knocked it over once! closed, luckily...)

neki desu said...

i've been experiencing the same woes as you re "flower" and vat color. from observation i have a feeling this has to do with the amount of indigo used and the quality, but i might be wrong.

Eva said...

neki - in my experience the lack of flower doesn't mean the vat won't dye but I've never worked with other vats so can't compare what difference the flower makes, if any.

heli said...

Wow, I love the process although it looks quite complicated for me! I would love to try myself once, but for now I just bought some japanese indigo seeds and they are growing, so we will see, what can I do with them :))).

Eva said...

heli - dyeing with the fresh leaves is fun! happy growing :)

k said...

i'm very curious to try this. I would like to have a big outdoor vat but i think this sounds like an approachable way to start. thanks very much for your tips!

Anonymous said...

Iam restarting my old ferment. vat in a gallon jug.
LIke your tall one. Have added water and old banana and found some of my madder.
Wonder when is good to add air and when best to not.
Mine is dark blue now. will find our heating pad to try warming it.
Be well
Lynn D

knittingiris said...

i, too, have tried a vat once but had little success as i had trouble keeping it warm enough, even in the winter, right next to the woodstove. since then, i've picked up an old heating pad but haven't gotten around to doing another batch even with having all the 'ingredients' on hand for some time now.
i've considered using the greenhouse to heat the vat during the heat of the day, but temps here regularly drop into the 40F range at night, even in midsummer.
i'm liking the haybox idea. it sounds a little like how i make yoghurt: inside mason jars set in a cooler full of hot water for 4-8 hours.
i don't quite understand the whole indigo fermentation process either. you have me curious enough to have another go at it now. thank you for sharing your experiences here.

knittingiris said...

one question: when you are doing repeated dips, when you say 'let the vat rest...during the day' does that mean that you allow the vat to cool and then reheat again before the subsequent dips/soaks?

Eva said...

Lynn D - good luck with your renewed vat! I don't know about oxygen. I've seen vats being stirred vigorously to add it during the early stages of fermentation (I guess). I just stir mine gently from time to time, usually after adding something or other.

knittingiris - glad you feel like having another go. I hope the haybox helps. During the days when I dye I keep the vat warmed up all the time whether there's fabric in it or it's resting. I only let it go cold when I'm not going to use it for a longer time.

leFiligree said...

i have finally removed the shibori tank top from my indigo vat. i plan to refold it and clamp it with a smaller board, but the results were good considering i keep the vat outdoors and the brew hadnt been renewed since last summer.

hope all is well with you.

Anonymous said...

I'm trying quite a large vat indoors. I started it off in my studio, but it was way too cold (colder than outdoors, poor me). So I've moved it home. I have bought an immersion heater from a homebrewers shop online. It is thermostatic and is factory set at around 24c, however you can manually crank it up somewhat. There is no dial, you just have to switch it off, let it cool, take it out, crank it up a bit, put it back, let it heat up, take temperature, repeat if necessary. I have now managed to get the vat up to 34c, which I think is still a little cool, but I'm hoping it's going to work.
Your description of the 'thickness' and feel of the liquid is really useful. Thank you!

maytemorel said...

I have a fermented vat that i have been babysitting and keep outside most of the time - covered - i have gotten great color out of it but now i am wondering if it possible to add more powdered indigo to darken the stock. not sure how to do this - let me know if anyone has tried.

Molly de Vries said...

Im attempting this as we speak, I have a 55 gallon drum using composted japanese indigo leaves, wood ash lye, lime stone and bran. I have been working on this for one month tomorrow. I'm still hopeful but its scary for me. even though we are doing different kind of vats it still helped me to read your understanding of fermentation. I am very lost and wish you were standing here with me. If I got into my details it would be a too much. for now a lttle pray wouldn't hurt. Always have loved your work. Molly

Anonymous said...

Can I get a recipe of Indigo vat?
I want to make it really really.