Indigo Vat Troubleshooting: Sludge and Sediment

Q: I was wondering if you may be able to help me troubleshoot my 5 gallon indigo vat issues? I purchased your beginners kit and all was working out well. Then, after a week or so my vat was just dark blue/ gray in appearance and the new fabrics were taking on a little blue pigment, but not really getting darker after many dips. I thought maybe the vat became oxidized, so I tried to follow your steps to solving oxidation (decant a gallon, heat to 180F, add 66 g iron and 100 g lime, used an immersion blender to mix). After adding that to the original vat and mixing all, my vat looked brownish in color, like mud/sludge. I let it to settle over night and it looks separated, clear like liquid on top and I see brownish sludge starting about half way down, taking up the bottom half of the 5 gallon indigo vat.

Might you have an idea of what is happening and how I might be able to fix/ revive my vat? I did measure my fabrics and I believe I have only dipped about 3.3 pounds in total (cotton/ linen).

A: I’m now a firm proponent of reheating the entire vat as a way to revive it. I use stainless steel pots and this is one of the only really logistically uncomplicated ways of doing this. So I would recommend getting yourself a stainless steel pot 25 to 30 quart, if you don’t already have one.

If you raise the temperature of the entire vat up to about 125 degrees while stirring every few minutes to keep the sediment up in suspension, you’ll see that the vat really “comes back to life”. Once it is up to temp, I cut the heat and let the sediment settle (for at least an hour and probably two hours is better). Then I dye in the clear liquid at the top.

There is also a possibility that you’ve exhausted all of your pigment depending on how much coverage (and how dark) you’ve dyed your pieces.