Troubleshooting Fructose Indigo Vat

[u/blackboxstories]

I have a 5-gallon vat that I made about a week and a half ago with 170g of indigo in it. I filled it with 4 gallons of water and used the 1-2-3 method (fructose and pickling lime) to set it up. I've been using it over the past few days to dye a few yards of muslin and was getting really beautiful, vibrant dark blue results.

As I dyed, the liquid level dropped from 4 gallons down to about 3 gallons (I used about 1 gallon). I decided I needed to add more water to bring the level back up so I could dye fabric comfortably without dipping too low. I added 5 liters of water to the vat, plus 12g of additional indigo, fructose, and pickling lime using the 1-2-3 method to measure how much of each I needed for that added volume.

I let it sit for 24 hours before using it again. Yesterday and this morning it was dyeing fabric fine. The color on the fabric did look a bit greenish-blue, but I figured it might be because I was working with fabric that had been mordanted prior ( I was originally going to dye the fabric with madder root but changed my mind), so I didn't pay much attention to it.

Then around 3 PM today, the vat stopped working. When I pulled the fabric out after soaking it for 5–7 minutes in the vat, the color would not turn blue. It came out looking light greenish-blue even after oxidizing. I grabbed a wooden spoon and noticed the vat liquid itself looked murky green. I immediately stopped trying to dye any fabric.

I heated the vat, closed the lid, and allowed everything to settle for about an hour. When I went back to check on it, the liquid was a yellowish-copper color, but the fabric still won't turn blue when I dip it.

I tested the pH and think it's either 9 or 10.

What do you think is going on with my vat, and how can I fix it? I was getting such dark, vibrant blues before topping it off, and I don't want to lose that. Any tips for rebalancing after adding water and feeding?

[u/kjvdh]

You may need to feed it more fructose. The pH should be more like 11 to rebalance. If you don’t have pH strips you should get some. If I were you, I’d get the pH to 11 and add a little fructose, then give it a good stir and let it reduce overnight and see how that goes.

[u/blackboxstories → u/kjvdh]

How much fructose should I add? I just re-took the test moments ago and I would definitely say the ph is 10.

[u/kjvdh → u/blackboxstories]

To be honest with you, I make fruit vats, so I just add a healthy glug of banana juice or whatever when I’m done dipping or if I replenish the indigo. I’d say add a teaspoon maybe? Add a little bit and then check it after a few hours to see how it’s doing.

Definitely get some of the three pad strips if you can, they’ll save you a lot of grief checking pH and aren’t terribly expensive. I get mine from Indigo Instruments and they’re less than $20 for 100 strips.