This post will probably only interest dyers who use an iron indigo vat, or a 1-2-3 vat as Michel Garcia calls it.
The iron vat is a great one. It requires very little maintenance. The blues you can get are deep and rich. The vat stays at room temperature so you can use clay or rice resists without fear of them boiling away. The downside is that it's got a ph of about 11 and needs to be soaked in an acid bath to get the ph down. Iron is used as a mordant with vegetable dyes to "sadden" them. You can get gorgeous warm tones that are a bit drab and toned down. In the indigo vat this makes your whites a bit dingy, and your blues a bit dusty.
After 20 minutes in a pot of hot water (ideally boiling, but I'm often lazy) the whites are clear and the blues are keyed up and vibrant. And the rinse water, which started out clear, looks like this. I did 4 loads in the bucket today, so it's murkier than usual, but it's pretty remarkable that this came out of the dyed fabric that looked pretty white. The good thing is that you don't need to do the rinse immediately. As pieces come out of the vat I toss them in a basket and periodically take a sunny morning, like today, and have a rinse session. I use a white construction bucket, hottest tap water and a few shakes of citric acid. I test to be sure the ph is around 4 or 5, although you can tell if it's working by whether the rinse water takes on the iron color after a few minutes. Some things I'm very specific about weighing and measuring. When eyeballing works, I'm all for it. I let the pieces soak in the acid rinsevfor about 20 minutes and then rinse them in clear water. S