Ambrotypes are extensions of the wet collodion process invented by Frederick Scott Archer, in 1848. While Archer was the first to experiment with the technique, the American James Ambrose Cutting patented refinements of the process, in 1854, attaching his name to the process. Sometimes called a collodion positive, an ambrotype is created by intentionally underexposing a glass negative and placing it against a darkened background. The light gray image recorded on the glass plate has the visual effect of a positive when viewed against a darkened back. This can take the form of fabric, paper, or even lacquer painted onto the uncoated side of the plate.
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