Hi VRDubb02,
I thinned my nailpolishes with regular thinner, I always use an A brand and not something you could buy at the supermarket.
The most nailpolish I have is very thick so I use a lot of thinner to thin it. I usualy thin it until it is as thin as water.
The first step I take is to spray the bodyparts with real carprimer, after that has dried and polished I spray a black or white base coat car paint to the parts. After drying and polishing I spray some mist coats of the thinned nailpolish to the parts, sometimes I spray four of five coats.
These coats are drying very fast so you could spray then in a short timeperiod. Be aware because nailpolish will dry like a matt or semi gloss coat. So I always spray some real car clear coat to the parts. Let them dry for a couple of weeks and then rubb it out.
A singel action airbrush will give a great result, I'm sure.
Be carefull with spraying nailpolish!! It is very toxic stuff in combination with thinner this is a breathtaker. So use a very good gasmask!!
Good luck with it!!
