Ambrotype

noun

1. An early type of photograph made by imaging a negative on glass backed by a dark surface.
2. In photography, a picture made by applying a dark backing to the face of a thin negative on glass.
3. A picture taken on a plate of prepared glass, in which the lights are represented in silver, and the shades are produced by a dark background visible through the unsilvered portions of the glass.
4. an early type of photograph in which a glass negative appears positive when displayed on a black background