Lippmann plate
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Named after Gabriel Lippmann, physicist. The Lippmann plate was an early form of colour photography developed in 1891.
A glass plate is coated with transparent and grainless silver emulsion. It is the uncoated side which is exposed to the light with the emulsion in contact with a reflecting surface such as mercury. The incident light is reflected back on itself causing interference. This establishes standing waves in the emulsion at half the wavelength of the incident light which react with the photosensitive emulsion. The plate is then processed so that the recording becomes changes in the index of refraction of the gelatin. These changes of index of refraction reflect the light by a process called Bragg Diffraction.
The color image can only be viewed in the specular reflection from the plate, making the field of view limited.
However the technique was very insensitive with the emulsions of the time and it never came into general use. RGB photography won because it was adequate for most purposes.
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