After texting with the dyer fellow, Graham Keegan, about my colours of indigo becoming greyish and losing the intensity of the blue, he suggested another top up of iron/calx. That seemed to work a bit but what really helped was a little bit of extra iron and some minor addition of oxygen. I think my vat was a bit over-reduced! Who knew that could happen? (Apparently the people over at Dharma Trading Co knew.)
Dani at Maiwa fine-tuned some questions for me and now the iron vat is purring along and producing knock-out blues. Dani and Sophia are a wealth of dyeing knowledge. No more synthetic indigo, for me.
I chose the iron indigo vat because it can work cold, and the others need to stay warm. The iron vat is also good for resist, because the resists can disintegrate in warm vats.
My fav resources are: