Honestly folk, try the gum arabic, you can get it anywhere that sells decent watercolour paints, it dries super quick and it goes on smooth. You can re-constitute it when dry, so you don’t have to worry about PVA drying out or going gluggy and wasting your mix. The quantities don’t have to be exact at all; because the medium dries so thin that it won’t get in your way, and it takes very little to be an effective binder. Just add a few of drops of the gum arabic to a couple of spoons of the TO2 and a lil water to bring it to a paint-like consistency and apply with a wide brush.
Gum arabic is the medium that turns pigment into paint (watercolour or gouache).