Gabriel Lippmann conceived a two-step method to record and reproduce colours, variously known as direct photochromes,[1] interference photochr

Lippmann plate - Wikipedia

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2021-06-19 20:00:03

Gabriel Lippmann conceived a two-step method to record and reproduce colours, variously known as direct photochromes,[1] interference photochromes,[1] Lippmann photochromes,[1] Photography in natural colours by direct exposure in the camera[1] or the Lippmann process of colour photography.[2] Lippmann won the Nobel Prize in Physics for this work in 1908.

A Lippmann plate is a clear glass plate (having no anti-halation backing), coated with an almost transparent (very low silver halide content) emulsion of extremely fine grains, typically 0.01 to 0.04 micrometres in diameter.[3] Consequently, Lippmann plates have an extremely high resolving power[4] exceeding 400 lines/mm.

In Lippmann's method, a glass plate is coated with a "grainless" (ultra fine grain [5]) colour-sensitive film using the Albumen Process containing potassium bromide, dried, sensitized in the silver bath, washed, irrigated with cyanine solution, and dried. The back of the film is then brought into optical contact with a reflective surface. This is done by mounting the plate in a holder of special form with pure mercury behind the film. When it is exposed in the camera through the glass side of the plate, the light rays which strike the transparent light-sensitive film are reflected back on themselves and, by interference, create standing waves.[1] The standing waves cause exposure of the emulsion in diffraction patterns. The developed and fixated diffraction patterns constitute a Bragg condition in which diffuse, white light is scattered in a specular fashion and undergo constructive interference in accordance to Bragg's law.[6] The result is an image having very similar colours as the original using a black and white photographic process.

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