A photogram is a photographic image made without a camera by placing objects directly onto the surface of a light-sensitive material such as photographic paper and then exposing it to light. The usual result is a negative shadow image that shows variations in tone that depends upon the transparency of the objects used. Areas of the paper that have received no light appear white; those exposed through transparent or semi-transparent objects appear grey. The technique is sometimes called cameraless photography. It was used by Man Ray in his exploration of rayographs. Other artists who have experimented with the technique include László Moholy-Nagy, Imogen Cunningham and Pablo Picasso. Variations of the technique have also been used for scientific purposes.