Glass positive

From 1850 onwards flat sheets of glass were used as supports for light-sensitive materials used in photography. They were used for positives, like the ambrotype, or more frequently, for photographic negatives. Albumen, collodion, and gelatin carrying light-sensitive silver salts have all been successfully used for coating glass plates to use in the camera. The term 'glass plate' most often applies to the collodion process.