if any of you started a natural fermentation vat of your own, by now it may be ready to dye.
the vat is ready when all (or at least most) of the oxygen has been reduced out of it. indigo dyeing is quite magical - the actual dyeing takes place not in the vat, like an immersion dye, but when the fibres are lifted out of the vat. the oxygen hits them and they turn blue.
the first sign that things are going well with your vat is that you will have a kind of coppery sheen on the top of it - this may happen in the first few days even. you know how gas spilled on the sidewalk has kind of a rainbowy, shimmery quality to it? like that.
but to know that your vat is actually ready to go, simply take up a small scoop of the liquid in a clear container. when healthy, the vat liquid will no longer be blue, but a greenish, yellowy blue, or if very healthy, amber. jim liles always describes the colour as dark beer colour.
and of course the ultimate test is to stick a piece of fabric in there. i have a pile of the selvedge edges of white fabric that i use to test my vats. stick a piece of fabric in there, and after a few minutes when you pull it out it should be a bright, vibrant, sometimes almost neon green. and then the magic. the colour will slowly shift before your eyes and become the beautiful blue that is indigo.
i tried to take a photo to show this, and didn't have too much luck, since the colour shifts pretty quickly, but you can get a bit of the idea here. the fabric on the left has only just began to turn blue, while the piece on the right is fully oxydized.
if you take your fabric out and it is already blue, or the liquid you take up in a container is still blue - your vat is not ready, and the dye will not stick. the oxygenation process has to happen.
in other types of vats, like the zinc-lime, another sign of health is that a 'flower' forms on the top of the vat. this will depend partly on the size of your vat - when i did my very tiny glass jar, the surface of the vat was quite small and i would only have a few little bubbles on the top. but now that i have a bigger vat going, i've also got quite a nice little flower happening:
but, i will note that the flower on my fermentation vat is much smaller (about 2 inches across), then the one on my zinc-lime vat (about 5 inches across), even though the vats are now the same size. photos of my zinc-lime flower, by much more skilled photographers than me, are here and here.
fingers crossed that your vats are happy!