Kodachrome Film

Kodachrome is the trademarked brand name of a type of color reversal film that was manufactured by Eastman Kodak from 1935 to 2009. Kodachrome was the first successfully mass-marketed color still film using a subtractive method, in contrast to earlier additive "screenplate" methods such as Autochrome and Dufaycolor, and remained the oldest brand of color film.
Unlike transparency and negative color films with dye couplers incorporated into the emulsion layers, Kodachrome had none. The dyes were formed during processing. Without couplers, the emulsion layers were thinner, causing less light scattering and allowing the film to record a sharper image. A Kodachrome slide is discernible by an easily-visible relief image on the emulsion side of the film. Kodachrome has a dynamic range of around 8 stops, or 3.6-3.8D.


Complex process of developing:

First, the antihalation backing was removed with an alkaline solution and wash. The film was developed using a developer containing phenidone and hydroquinone, which formed three superimposed negative images, one for each primary color.

After washing out the first developer, the film underwent re-exposure and redevelopment stages. Re-exposure exposed the silver halides that were not developed in the first developer, effectively fogging them. A color developer then developed the fogged image, and exhaustion products formed a dye in the color complementary to the layer's sensitivity. The red-sensitive layer was re-exposed through the base of the film with red light, and then redeveloped forming cyan dye. The blue-sensitive layer was re-exposed through the emulsion side of the film with blue light, and then redeveloped with a developer to form yellow dye. The green-sensitive layer was redeveloped with a developer that chemically fogged it and formed magenta dye. The two light re-exposures had to be carefully controlled so as not to cause re-exposure of the green-sensitive layer.

Following color development, the metallic silver was converted back to silver halide using a bleach solution. The film was then fixed, making these silver halides soluble and leaving only the final dye image. The film was finally washed to remove residual chemicals which might have caused deterioration of the dye image, dried and cut.

- Nicole