Lippmann plate
Lippmann process photography is an early color photography method and type of alternative process photography. It was invented by French scientist Gabriel Lippmann in 1891 and consists of first focusing an image onto a light-sensitive plate, placing the emulsion in contact with a mirror (originally liquid mercury) during the exposure to introduce interference, chemically developing the plate, inverting the plate and painting the glass black, and finally affixing a prism to the emulsion surface.