Liquid Decal Film

Thanks for all your replies. I finally slowed down and did some actual compatibility testing.

The stuff is completely incompatible with all water based solvents—has to be, it's used to make decals!

It's compatible with 90 % isopropyl alcohol, mineral spirits, and lacquer thinner, as tyamada indicates. It does not appear to be compatible with ethyl or denatured alcohol.

Lacquer thinner might attack the inks in some decals, but mineral spirits would slow drying.

I think I'll just brush it on, neat.

Microscale Decal film is a type of varnish and can be thinned with alcohol or lacquer thinner.  If you thin it with alcohol don't brush it on inkjet printed decals, the water in the alcohol will cause the ink to run.  If you thin it with lacquer thinner it souldn't be a problem. 

I suggest brushing it on with a 3/8 soft flat. That works the best for me. But make sure to do two coats, the stuff sticks better to itself than paint or plastic. If you must airbrush, I would try water and thouroughly mix it, then clean the AB with some windex.