conceived a two-step method to record and reproduce colours, variously known as direct photochromes, interference photochromes, Lippmann photochromes, Photography in natural colours by direct exposure in the camera or the Lippmann process of colour photography. Lippmann won the Nobel Prize in Physics for this work in1908. A Lippmann plate is a clear glass plate, coated with an almost transparent emulsion of extremely fine grains, typically 0.01 to 0.04 micrometres in diameter. Consequently, Lippmann plates have an extremely high resolving power exceeding 400 lines/mm.
Method
In Lippmann's method, a glass plate is coated with a "grainless" 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. 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. The result is an image having very similar colours as the original using a black and whitephotographic process. For this method Lippmann won the Nobel Prize in Physics in 1908. The colour image can only be viewed in the reflection of a diffuse light source from the plate, making the field of view limited, and it cannot be copied. The technique was very insensitive with the emulsions of the time and it never came into general use. Another reason Lippmann's process of colour photography did not succeed can be found in the invention of the autochrome plates by the Lumière brothers. Lippmann photographic techniques are being developed to produce images which can easily be viewed, but not copied, for security purposes.
