To achieve the in-camera effect, a reel would be made up of pre-exposed and developed film, and unexposed raw film, which would then be loaded into the camera. The exposed film would sit in front of the unexposed film, with the emulsion of both films touching each other, causing the images on the exposed film to be contact-printed onto the unexposed stock, along with the image from the camera lens. This method, in conjunction with a static matte placed in front of the camera, could be used to print angry storm clouds into a background on a studio set. The process differs from "optical printing" in that no optical elements (lenses, field lenses, etc.) separate the two films. Both films are sandwiched together in the same camera and make use of a phenomenon known as "contact printing".