Agfacolor Neu: dye couplers in the film
1936
Agfa put the colour-forming couplers into the three layers of the film itself, so colour film could be developed with one set of chemicals. Most later colour films worked this way.
How it began
The idea of forming dyes during development dates from Rudolf Fischer in 1912, but the couplers would wander between layers. Kodachrome (1935) avoided this by adding the couplers in processing, which needed complex laboratory machines. In 1936 Agfa chemists found ways to anchor the couplers in each layer of the film.
How it works
The film has three emulsions, sensitive to blue, green and red. As the developer turns exposed silver into metal, its by-products react with the coupler in that layer to form a yellow, magenta or cyan dye. The silver is then bleached away, leaving a dye image.
Why it mattered
Processing became simple enough for ordinary labs, and later for amateurs. After the Second World War Agfa’s patents were taken as reparations, and its approach became the basis of most colour films worldwide, including colour negative film.
Limits and what replaced it
Early dyes faded and colours were less saturated than Kodachrome. Improved couplers and the C-41 and E-6 processes refined the method rather than replacing it.
Today
Colour negative film and most slide films still carry their dye couplers in the emulsion, as Agfa did.