Airbrushing at a constant 25 psi (pounds-per-square-inch) would be similar to driving your car at a constant 25 mph. You can as long as you drive a straight road, but stopping or turning sharply is a chore. Likewise, pressure set at a constant 25 psi works great for a certain specific set of circumstances, but that’s about it. Analogies aside, air pressure regulation is probably one of the least understood, most underrated aspects of attaining success in airbrush art. Air pressure is highly dependent on two things: the viscosity of paint, and your type of substrate (automotive surfaces, T-shirts, canvas, illustration board, etc). For example, I use 50 to 70 psi when airbrushing T-shirt paint straight from the bottle, which is ideal to siphon the paint, atomize it correctly to achieve a complete range of lines and shading, and to force the color into the fabric. For fine line work with a thinner medium, such as a transparent ink or an aniline dye, onto a paper or board, the air pressure should be lowered to about 10 psi, giving more control and preventing any “spidering,” where the paint spreads in all directions on impact. The pros adjust air pressure to as low as 1 psi and as high as 90 psi. If your airbrush is clogging with thicker paint, try increasing the air pressure until the problem stops. Experimenting with air regulation is one of the most important aspects of airbrushing. Controlling the air pressure is key to performing various textures and spray patterns.
FOR ALL THINGS AIRBRUSH:
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Airbrush Action Magazine: http://bit.ly/1gGWzny
Airbrush.TV: http://www.airbrush.tv/ (largest selection of online instructional videos on airbrushing.)