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.