TL/DR – 1) Interesting technical discussion of one of the earliest color photography methods and 2) a great website that covers alternative photography.
Mr. Lippmann won a nobel prize for developing a color photography technique in 1908. He used a interference of light technique where light coming into the glass plate film was also bounced off a mirror behind the plate and thus the image recorded was the resulting combination of incoming light and reflected light. This technique takes advantage of two properties of light – the wave function, and the fact that wavelength is color dependent and speed of light through different materials is wavelength dependent. This technique needs the light to come into the plate at an angle off the lens axis in order to separate the colors, and also needs to be viewed at the same angle the light was recorded with. Some shared characteristics with Holograms in that the interference pattern of the light is recorded.
Please do check out the Alternative Photography website as it’s a great resource for learning about all kinds of different alternative photography techniques from Antrotypes to Wet plate.