Ambrotype is a mid-19th century photographic process introduced in 1851–1852 by Frederick Scott Archer and Peter Fry. The technique used a weak collodion negative placed on a glass plate, which was then backed with a dark or black surface to create the appearance of a positive image. Ambrotypes were popular for portrait photography due to their relatively quick exposure times and distinctive, high-contrast visual effect. They are an important part of photographic history, representing early experimentation with glass plate processes, and are still studied and reproduced today by collectors and practitioners of historical photographic techniques.