An ambrotype is an image made by placing dark paper behind a glass negative; when seen in the proper light, the image appears positive. Boston photographer James A. Cutting took out a patent for this process in 1854. Over the next decade, many photographers sold ambrotypes in velvet-lined leather cases with brass mats. In this form, they resembled daguerreotypes, though they were cheaper to buy and simpler to make. Ambrotypes remained a popular for of portraiture through the Civil War, but became obsolete soon afterward.
1. John C. Fremont / Mathew Brady Studio