Hi Troops:
I should save this as a basic file and post it about every three months, it keeps coming up again and again.
"Liquitex Low Viscosity Acrylic Air Brush Medium", I bought an 8 oz. bottle at Michael's. A blend of Acrylic polymer emulsion and flow agents designed to enhance the spraying of acrylics. I have even airbrushed old Poly-S paints quite well and they were originally formulated for hand brushing. FWIW I have used this with most acrylics except Tamiya. I have been told that it does not work well with Tamiya paints.
Bill Shuey