Lippman 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 deposited silver then reflects light at various multiples of the original wavelength giving rise to bright colours.

However the technique is very insensitive and requires special equipment for viewing and it never came into general use.