Keystone Views - Fine Art Prints of Historical Photos
Keystone distinguished itself by pursuing the educational market, preparing teachers’ manuals to accompany their stereograph and glass slide collections, and popularized the box sets initially introduced by Underwood & Underwood.
Later, when stereoviewing was declining, Keystone bought the stocks of the other major publishing companies -- including B. W. Kilburn, H. C. White, and Underwood & Underwood. As a result, Keystone had over 50,000 numbered views available by the 1930s.
Finally bowing to changing times, Keystone stopped regular production of stereographs in 1939, but filled individual orders until 1970.