This photograph shows a typical field setup of the Civil War era. The wagon carried chemicals, glass plates, and negatives - the buggy used as a field darkroom.
Example of a Wet Plate Photograph
(Library of Congress, Prints and Photographs Division)
Before a reliable, dry-plate process was invented (ca. 1879) photographers had to develop negatives quickly before the emulsion dried. Producing photographs from wet plates involved many steps. A clean sheet of glass was evenly coated with collodion. In a darkroom or a light-tight chamber, the coated plate was immersed in a silver nitrate solution, sensitizing it to light. After it was sensitized, the wet negative was placed in a light-tight holder and inserted into the camera, which already had been positioned and focused. The "dark slide," which protected the negative from light, and the lens cap were removed for several seconds, allowing light to expose the plate. The "dark slide" was inserted back into the plate holder, which was then removed from the camera. In the darkroom, the glass plate negative was removed from the plate holder and developed, washed in water, and fixed so that the image would not fade, then washed again and dried. Usually the negatives were coated with a varnish to protect the surface. After development, the photographs were printed on paper and mounted.