The glaze is thin in the sense that it has low viscosity and in the sense that it is see through. Note the difference between a glaze and a wash. This is on the border.
For my first go, I tried adding some retardant too: don't! For the first time, I managed to make some paint that never dries. The airbrush medium is quite slow drying anyway.
I wonder if airbrush medium plus grey might be a solution for the tricky problem of shading white.