There is not really a formula per se; however, what I do is just add more of the 1:3 Galkyd Gel:cwm mixture to my paint, which dilutes the paint - even the more opaque ones - so there is so much less pigment and this make it a glaze. More often than not, I keep the cwm/ggel ratio consistent throughout the painting, and just add more to the paint (ie, more than the usual 1 part cwm to 1 part paint - just for the glazing process). Usually the glazing process comes toward the end of a painting and it is a very thin layer, so this should all be fine but if you do a glaze earlier on, usually a glazed layer is pretty thin as well.