Stereographs

Two nearly identical photographs or photomechanical prints, paired to produce the illusion of a single three-dimensional image; usually viewed with a stereoscope. Typically, photographic prints on card mounts, but may be daguerreotypes, glass negatives, or other processes. Card mounts commonly 3.5 x 7 in. (9 x 18 cm.) up to 5 x 7 in. (12 x 18 cm.). Popular in the United States 1859-1920s.