There are many opinions on setting the "right" air pressure for the airbrush, but there is no "one size fits all" psi setting.
There are just too many variables. Different airbrushes require different pressures, which depend on the paint chemistry and the amount of reducer in the paint, and some claim even the relative barometric pressure plays a part.
Too little pressure
With too little pressure, the airbrush will fail to atomize the paint, and instead of a nice smooth delivery, the paint will create a coarse, textured finish. Of course, this might work well where a grainy finish is desired, but not at all if you are looking for a smoother, less textured, result.
Too much pressure
Too much pressure creates splatters and blowouts, where the force of the air pushes the paint away from the target before the paint has the opportunity to dry.
So how do you arrive at the optimal psi?
First, let's ignore our air pressure gauge. We are going to set our pressure based on how the airbrush is performing with the paint inside it. Bear in mind that these settings will no longer apply if you change the paint or add reducer.
First, set a relatively high pressure. One that easily atomizes the paint. Then gradually begin lowering the air pressure bit by bit until you see the atomization fail. I usually go one-quarter of a turn of the regulator at a time. Once you've found that threshold, crank up the pressure just slightly so that the airbrush atomizes once more, and you are set!
