2011-04-04

Kodacolor and Ektachrome

The story so far: In 1912 Rudolf Fischer invented the modern "chromogenic" color film<. However, he could not prevent the crucial color couplers to migrate between the different gelatin layers. Therfore he had no technical solution for his otherwise so brilliant idea. It took about 20 years unless the two companies Agfa and Kodak independently overcame the issue using different chemistry and processes. In 1935 Kodak was first on the market with the Kodachrome reversal film. The color couplers were introduced into the film layers in a very complicated multistep process during film development.

The Agfa researchers actually came closer to Fischer's basic idea and solved the issue with so-called "diffusion resistant couplers" and designed a pretty simple process. In 1936 the "Agfacolor Neu" film was launched on the market. During the following years (and even decades) the two  companies gave each other a technological race, which always brought further improvements. Eventually, and about 50 years later Kodak won the race when Agfa and other companies switched to Kodak's chemistry and labs would only take this type of film. Key for this victory was a new method adopted in 1940 using "oil protected couplers".  It was the basis for Kodak's Kodacolor (negative) and Ektachrome (reversal) films and is actually the only (analog) color film technology still in use. 
Again, catalyst for the development of the new method was the war. With the Agfacolor technology Hittler-Germany had a color material relatively easy to process, a big advantage at the front where the soldiers could process their images by themselves. The competing Kodachrome, although higher in resolution, had to be processed at some few specialist Kodak laboratories. Therefore the American army entrusted Kodak with the development of a new film material especially for aerial reconnaissance. Top priority was the ability of easy in-the-field processing. Beginning in 1940, the Kodacolor Aero Reversal film was available for the desired purpose. The technology was based on an idea by the English chemist Michele Martinez. Kodak aquired his 1937 patent application US 2,284,877. The Kodak researchers Edwin E. Jelley and Paul W. Vittum refined the process further (US 2,322,027). Based on this technology Kodak launched negative films and photographic papers ("Kodacolor", from 1942) and later Kodak the Ektachrome series (reversal film, from 1946).
The idea behind the new method is brilliant. Like in the Agfacolor technology the specific (colorless) color couplers are a constituent of the respective three color-sensitive gelatin layers. They react with the oxidation product of the developer to form the final dye. The basic chemistry of the couplers are the same with Kodak and Agfa. However, the Agfa couplers need to carry a) long aliphatic tails that make them resistant to diffusion, and contain b) sulfonic or carboxylic groups to ensure water solubility. Kodak's chemistry is much simpler: The couplers are embedded in oily resins dispersed as small droplets within the gelatin layer. The couplers themselves have to have a solubility in organic oils and are thus protected from the diffusion into the aqueous environment of the development process. In contrast, the developer solution contains a solubilizer (eg. benzyl alcohol), to wrangle the oxidized developer in the oil droplets to react with the couplers.
Initially the Agfacolor method was superior to the Kodak method, since the oil droplet size determines the color granularity ("grain") of the film. Kodak learned over the years how to create and stabilize smaller and smaller droplets. Initially, Kodacolor was only offered as roll film as enlargements from 135 film would have looked ugly. However, gradually increasing speed and fine grain Kodak could eventually offer even the tiny negative size of the disc cameras. When the image quality fit, the economic benefits of Kodak's technology came to light. The couplers are chemically simpler and therefore less expensive to make. In addition, Kodak's development processes C-41 (negative) and E-6 (reversal film) are performed at 38°C, significantly faster (and cheaper) than the Agfa chemistry. Beginning in 1978, Agfa gradually introduced new film generations using the Kodak process (as well as almost any other film producer at the time did). The race was over...

Finally, here is probably the most famous photograph on an Ektachrome film: "Earthrise" taken on Christmas Eve, 1968 aboard Apollo 8 by William A. Anders, Hasselblad 500C, Carl Zeiss lens 250 mm, f/11.


For further reading (in addition to the links in the previous posts): An issue of Life magazine, June 12th, 1944 with the article about the Kodacolor Aero (p.53) and a full-page advertisement of the company Ansco (p.10), which used the Agfa process; Michael Talbert's Photomemorabilia; David Rogers' "The Chemistry of Photography" , RCS Publishing 2007. Ronald D. Theys and George Sosnovsky, Chem Rev. 1997, 97, 83-132.

Other parts of this little history series... 
1) Invention of the modern multilayer color film - 100 Jahre moderner Farbfilm
2) Kodachrome
3) Agfacolor Neu
4) Ektachrome and Kodacolor

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