Photographic plate

A rigid support, traditionally glass, coated with light-sensitive emulsion that records an image during exposure and development. Plates were widely used before flexible photographic film became practical.

Gelatin silver process: A photographic process in which light-sensitive silver halides are suspended in gelatin and developed into a silver image. Gelatin silver emulsion became the standard coating for many photographic plates.
Daguerreotype: An early photographic process that forms a unique image on a polished, silver-coated copper plate. It established the use of rigid plates for making detailed photographs, though its surface was metal rather than emulsion-coated glass.
Astrophotography: Photography of celestial objects and phenomena, often using long exposures or specialized instruments. Glass plates recorded faint star fields and enabled precise astronomical measurements.
Photographic film: A flexible transparent base coated with light-sensitive emulsion for recording photographic images. Film replaced fragile, heavy plates with a portable medium that could be wound through cameras.
Silver halide: A light-sensitive compound of silver and a halogen, used to form latent images in photographic materials. Silver halide crystals in the emulsion register light as a latent image.
Calotype: A photographic process patented by William Henry Fox Talbot in 1841, producing paper negatives from which prints could be made. Its paper negative offered reproducibility in contrast to the direct image of early plate processes.
Astrometry: The branch of astronomy that measures the positions and motions of celestial objects. Astronomers measured star positions on photographic plates across repeated exposures.
Sheet film: Individual sheets of flexible photographic film, commonly used in large-format cameras. It retained the plate’s one-image-at-a-time format while avoiding a glass support.
Latent image: An invisible chemical image formed by exposure in a photographic emulsion before development. Exposure changes the plate’s silver halides before any visible image appears.
Wet collodion process: A photographic process using a glass plate coated with collodion and sensitized shortly before exposure. Wet collodion made glass negative plates practical and produced detailed images.

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