There's not much of a "binder" in watercolor paints as they seep and bleed into paper. Other paints carry a binder that acts as an adhesive of sorts, some more tenacious than others. If the surface is porous, watercolor paints will be absorbed, if not, it just dries on top. The dials I've played with all had non-porous lume. That's why I ended up mixing my watercolor paints with titebond III glue thinned out quite a bit with water, to add the binder/adhesive. This method doesn't let you rinse off the color after the application but can be peeled off after it dries if you're not happy with the result. That said, it's pretty forgiving as it dries and you can guide the drying paint with a sharp toothpick or fine brush.I think i am going to switch to this method. The paint with brush and wash does not seem to work for me. I am missing something here about it.
Titebond III dries a light mustard color when dry but I imagine any white glue, like Elmer's, would work too. I'm considering Elmer's for actual lume binder as it's clear when it cures.
Long live research and develpoment