Shotblasting consists of attacking the surface of a material with one of many types of shots. Normally this is done to remove something on the surface such as scale, but it is also done sometimes to impart a particular surface to the object being shot blasted, such as the rolls used to make a 2D finish. The shot can be sand, small steel balls of various diameters, granules of silicon carbide. The device that throws the shot is either a large air gun or spinning paddles, which hurl the shot off their blades.