Lippmann plate

Gabriel Lippmann conceived a two-step method to record and reproduce colours, known as:
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. Consequently, Lippmann plates have an extremely high resolving power exceeding 400 lines/mm.