A reproduced photographic image created from a glass plate, it differs from a daguerreotype, which was made from a highly polished metal plate. Source: Fern and Kaplan, "Viewpoints" (Collection of Library of Congress)<br><br>A photographic process introduced in 1851-52, which quickly replaced the earlier daguerreotypes because they were cheaper and easier to view. It used weak collodion negatives which were then bleached and backed by a black background which produced the effect of a positive image.