photographic plate

a flat, light-sensitive sheet of glass or plastic coated with a photographic emulsion

A photographic plate is a flat piece of glass or metal coated with a light-sensitive material used for capturing images in early photography. When exposed to light through a camera, the plate records the image, which can then be developed to produce a visible photograph. Photographic plates were widely used before the introduction of film and were valued for their high image quality and detailed resolution.