StereographsFirst described in 1832 by English physicist Sir Charles Wheatstone, stereoscopy was improved by Sir David Brewster in 1849, and was popular in the United States and Europe from about the mid-1850s through the early part of the 20th century. Similar to card photographs, “stereograph” refers to a format, not a technical process.
Process. Many different processes, in fact, were used to produce stereograph cards; daguerreotypes and ambrotypes were used to create stereographs up to the early 1850s, and glass stereographs were in use from 1852 to 1860.
Identification. Regardless of photographic process, stereographs are formed by placing two nearly identical images side by side often on card mount . These were most commonly produced with cameras that had two lenses side by side, 2.5 inches apart, so that two exposures were made simultaneously and in order to produce the effect of a three-dimensional image through a special viewer. Most commonly, stereographs were viewed on a hand-held stereoscopes, a device developed by Oliver Wendell Holmes in 1861; viewed on such a device, stereographs gave the image a sense of three dimensionality. Stereographs enjoyed popularity from the late 1860s until after the turn of the century (Ritzenthaler, et. al., 41).
Keystone View Company (1892–1972) produced stereographic sets for educational purposes, often times in combination with lantern slides. According to the company's publication, "American history; teachers' guide : a special set of 300 lantern slides and 300 stereographs," the set offered an opportunity to visualize historical issues. Keystone recommends, "The stereograph will be used first because it lends itself to individual study...[while the slide] can be presented enlarge to the entire class at once..." (Keystone View Company, 1925).