Indigo Vat Troubleshooting: Recipe Quantities for a Large Vat

Q: I am wondering if you are able to help me troubleshoot my vat. I made a 19 gallon iron vat in a plastic bin about a week ago with no success. I found instructions online that called for 20g indigo, 40g iron, and 60g lime for a 5 gallon vat, so I multiplied it by 4 for 19 gallons (80g indigo, 160g iron, and 240g lime). I see that this recipe has lower quantities of each than what you recommend and I am not sure why or if this is the issue. Initially the vat seemed to work. On the first day it had a coppery sheen but no flower and produced mid-dark blues. I dyed approximately 100g of fabric. On subsequent days, however, everything went downhill. I have continuously checked the pH, stirred, and added more iron and lime when I thought necessary. The vat liquid continues to be blue but I cannot get any good color when I dip. I tried restarting it by adding 1-2-3 solution again (as per your instructions). I am pretty sure the vat is not exhausted, but this still has not helped. I bought iron sulphate from a garden shop, it is ferrous (II) sulphate as far as I am aware. I am thinking of chucking out the vat and starting again by scaling up your recipe of 50g, 100g, 150g. Any thoughts?

A: No need to chuck! I'm going to assume that you actually have the right kind of iron, but definitely double check! It just sounds like your numbers are low for the vessel. I'd use at least 600g lime, 400g iron to properly reduce that amount of liquid (maybe more). If you've still got the vat, try decanting a gallon or two, heating to simmer, cut the heat then mix in another 450g lime and 300g iron (plus any additional indigo you may want). After ageing that for an hour or so (it will probably be a thick paste), add back to the large vat and stir thoroughly. It should dye well on the following day.