Thinning paints

Depends... I usually thin my enamels 1:1 with lacquer thinner, but have had excellent results thinning even more than that.

--- Tontoni

I start with about a 1:1 mixture (paint:thinner). However, since paints vary in thickness, especially with how many times they have been opened, I then sometimes have to adjust by adding either a bit of paint or a bit of thinner. This is for enamels. I don't airbrush much acrylic because of concerns about drying in airbrush.

Anything from none at all to 50:1. Depends on the paint brand, thinner, airbrush, air pressure, nozzle size, spraying distance, effect you want to achieve, subject, etc. And even if you take all that into account, your mileage may still vary...