An airbrush works by passing a stream of fast moving air through a venturi, which creates a local reduction in pressure (suction) that allows paint to be pushed up from a reservoir at normal atmospheric pressure. The paint is mixed with the air and blown through a very fine nozzle, which atomises it into tiny droplets. The paint is carried onto the paper or other medium. The operator controls the amount of paint using a variable trigger which opens more or less of the nozzle using a very fine tapered needle. This extremely fine degree of control is what allows an artist to create such smooth blending effects using the device.
The technique allows for the meshing of two or more colors in a seamless way, with one color slowly becoming another color. The images have a floating quality, with undefined edges between colors, and between foreground and background colors.
Airbrushing has long been used to alter photographs in the pre-digital era. In skilled hands it can be used to help hide signs that an image has been extensively retouched or "doctored". Many photographs of officials from the Stalinist regime show extensive airbrushing, often entire people have been removed. The term "airbrushed out" has come to mean rewriting history to pretend that something was never there.
This kind of picture editing is now usually done with Digital Imaging tools such as Adobe Photoshop, which are capable of even more subtle work in the hands of a skilled touch-up artist.
The airbrush led to the development of the spray gun, a larger, more industrial type of paint applicator used for larger areas. Airbrushing itself started being used on cars in the 1940s to make hot rods, specialty cars and then spread to the general car repainting industry.
See also:
Airbrushing for photo retouching
Spray guns
Many street artists use airbrushing to create names and pictures for tourists, such as around Jackson Square in New Orleans.