figured i would pop in quickly and answer the two questions that came from the last post, here, rather than in the comments sections.
nicole asked about the daily stirring - concerned that it would introduce oxygen into the vat, which is of course exactly what you're trying to avoid. i do what my instructor in art school taught me, and what i saw a very experienced indigo dyer in japan do - stir in a circular motion with a (very long) spoon that reaches to the bottom of the pot. this way, the spoon is mixing up the sludge that has settled at the bottom (which is the point of the stirring - to reintroduce the mix into the water to allow the chemical reactions to continue happening). and as you stir you begin to create a whirlpool - not only does this mix things up fairly aggressively without adding too much oxygen, but once you have a flower forming, the whirlpool helps to bring the flower back together into the centre of the vat.
i agree with margie that it's good to do your stirring at the same time each day - then it just becomes part of your regular daily routine. i do mine first thing in the morning - feels like a little check-in to see how they're doing....
and heleen asked if it was possible to use a big plastic bucket to make a vat in, which it definitely is. you can use any type of vessel you like. preferably one with a lid, to help keep both the air out and the smell in. currently both my natural fermentation and my zinc-lime vats are in 5 gallon plastic pails, the kind that a contractor or painter might use.
the main consideration when choosing a vessel is what you're going to dye. i had my fermentation vat in a smaller container (a stock pot), but then when i would dye large skeins of wool, the wool was too big and would touch the sediment at the bottom of the pot, mixing it all up, which you don't want to do while dyeing. your goods will not only get a bunch of unreduced indigo on them, which will make them look darker blue than they are but will then wash off when you rinse (and waste the indigo), but once the liquid gets too stirred up, you have to stop and let the sediment settle again, which takes at least two hours. so choose a vessel that is big enough that your fibres can go into it without touching the bottom two inches or so of the vat.
the other consideration is keeping the vat warm - the advantage of a stock pot or other metal vessel is that you can just plunk it on the stove to warm it up. but this time of year your vat shouldn't need any additional warming - summer room temperature will be more than enough. however come winter, a plastic vat will be harder to keep warm, and alive.
there's many wonderful photos of indigo dyers in warm climates, who have their vats built right into the ground, like this man in india:
photo from here