A: Spray at the lowest pressure that atomizes the paint to your liking.
Every color sprays a little differently. Lighter colors tend to give you more problems than darker colors. White tends to spray the worst and violet tends to spray the best. Black is weird, consider it a light color.
Air pressure is power. Power to drive the airbrush and atomize the paint. Without pressure spray equipment doesn’t work. However, everyone’s needs and goals are a little bit different. Because of this I can give my cop out answer “spray at the pressure that atomizes the paint to your liking”
There are some general guidelines though. Here they are.
When paint atomizes it forms tiny spheroid droplets of paint. The size of these droplets is determined by how much force (air pressure) blows apart the bigger droplets.
This is really a great benefit. Airbrushes clog. It’s a fact of life. The finer the grind on the paint pigments the less often your airbrush will clog (but that’s a whole other question). More air pressure can suck out some of the clogs before they have a chance to back things up.
This is also a great cleaning method to remember. When your airbrush is clogged and you know it’s probably some chunky paint, turn up the air pressure and see if you can just spray it out.
This happens more with urethane based paints, especially when using quick reducers, than it does with other kinds of paint. If the paint droplets are too small they will actually dry and harden before they hit the surface being sprayed. This makes a rough, sand-paper-like texture on the sprayed surface.
Imagine the difference between Disney’s Epcot Center and the top of the Astrodome sitting on your surface.
Less overspray let’s you spray finer, smaller details without as much need for friskets, stencils, and shields. This is a very good thing for people interested in the finer points of airbrushing.
Transfer efficiency, the amount of paint sprayed compared to the amount of paint that actually adheres to the surface being sprayed, is much higher when the paint droplets are bigger.
The less energy or force there is to atomize the paint the bigger the paint droplets. The bigger the paint droplets the coarser or rougher the visual spray texture will look.
The less energy there is to pull the paint the easier it is for the airbrush to clog. This makes straining and thinning your paint much more necessary than if you spray at higher pressures.
I always tell people to spray with as little pressure they can get away with but enough to do the job.
Here’s the method I use to figure out what pressure i should spray at.