Double action airbrush technique involves depressing the trigger on the top of the airbrush with the index finger to release air only, and drawing it back gradually to the paint release threshold. The most important procedural dynamic is to always begin with air only and end with air only. By observing this rule, precise control of paint volume and line width and character can be achieved. The single most important airbrush stroke consistently utilized by professionals is the dagger stroke. This describes a stroke which begins wide and ends as a narrow line, created by starting with the brush far from the support and moving it evenly closer as the line is drawn.
Single action airbrush technique derives its name from the fact that only one action is required for operation. The single action of depressing the trigger releases a fixed ratio of paint to air. Achieving different line widths requires either changing the tip and nozzle combination or else adjusting the spray volume manually between spray width changes. The most important aspect of proper single action airbrush technique is to keep the hand moving before the trigger is depressed and after the trigger is released. This avoids the "bar bell" line.