Sharpening Your Vat

Q: I'm wondering if you can keep an indigo and iron vat going by feeding it more after it’s exhausted of indigo or do you have to begin again from scratch once there's no indigo pigment left in it?

A: Yes, you can keep the vat rolling by "sharpening" it. Over time (after a couple rounds of sharpening) you will build up a bunch of sediment that will start to cling to the bottom of your fabrics and leave some "muddy" indigo tones. At this point, you do need to start from scratch, or just decant the clear liquid and discard the sediment, then top it up.

So, try adding all ingredients again in proportion. I decant some of the clear liquor (1-2 gallons) from the top of the vat into a stainless steel sauce pot that I've dedicated to dye use, heat to boiling, then remove from the heat and add the ingredients. Mix well (immersion blender without making bubbles if you've got one). Let that sit for a few hours until it is an insane neon yellow, then add back into the larger container.

Top up your vat with fresh, hot water to keep it near the brim.

You can then let it cool to ambient temperature and use as normal.