How were photograms invented?

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. In a darkroom, or a darkened room, objects are arranged on top a piece of photographic material, usually photographic paper. When the operator is satisfied with the arrangement, the photographic material is exposed with light, usually by switching on an enlarger or other artificial light source. The material is then processed, washed and dried.

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.