Water, flour, lemon and salt is all I know.
What are you using it for? It's pretty old school -- I'm wondering if you can get away with not doing it?
Oddly, it popped up on two different PBS shows yesterday. It one case it was the poaching liquid for the white parts of chard, followed by an ice bath. Then Pepin was using it, but I missed seeing what he was preparing. Maybe sole?
Yes, it's a technique used to keep white foods white when blanched. I learned it in cooking school, and never used it again!
You use it to poach white vegetables and you can also store those same white vegetables in the blanc in the fridge or freezer for months