Steps
The layers in the film are top to bottom; blue sensitive (yellow), yellow filter, blue-green sensitive (magenta), blue-red sensitive (cyan), acetate base, rem-jet antihalation backing.
The processing cycle is as follows:
- Backing removal
- An alkaline bath softens the cellulose acetate phthalate binder. A spray wash and buffer removes the rem-jet antihalation backing.
- First Developer
- All exposed silver halide crystals are developed to metallic silver via a PQ developer. The yellow filter layer becomes opaque because it has a combination of Lippmann emulsion (very tiny grains) and Carey Lea silver (metallic silver particles that are small enough that they are yellow rather than gray.)
- Wash
- Red light re-exposure through the base
- This makes the remaining undeveloped silver halide in the cyan layers developable.
- Cyan developer
- The solution contains a color developer and a cyan coupler. These are colorless in solution. After the color developer develops the silver, the oxidized developer reacts with the cyan coupler to form cyan dye. The dye is much less soluble than either the developer or the coupler so it stays in the red layer of the film.
- Wash
- Blue light re-exposure from the top
- This makes the remaining undeveloped grains in the blue sensitive layer (the yellow layer) developable. The now opaque yellow filter layers prevents the blue light from exposing the magenta layer (the green sensitive layer, which is also sensitive to blue light). It is important to avoid stray printing light exposing the film base of film.
- Yellow developer
- Analogous to the cyan developer.
- Wash
- Magenta developer
- This contains a chemical fogging agent that makes all of the remaining undeveloped silver developable. If everything has worked correctly, nearly all of this silver is in the magenta layers. The developer and magenta coupler work just like the cyan and yellow developers to produce magenta dye that is insoluble and stays in the film.
- Wash
- Conditioner
- Prepares the metallic silver for the bleach step.
- Bleach
- (Iron EDTA) Oxidises the metallic silver to silver halide. The bleach must be aerated. The former ferricyanide bleach did not require aeration and did not require a conditioner.
- Fix
- Converts the silver halide to soluble compounds which are then dissolved and washed from the film
- Wash
- Washes the fixer out of the film.
- Rinse
- Contains a wetting agent to reduce water spots.
- Dry
The result is three different color records each with the appropriate dye, just like other color films. The original Kodachrome process in 1935 used dye bleaches and was a far more complex process. Although the formulae have changed over the years, the basic process steps have followed a similar pattern since the introduction of "selective re-exposure" Kodachrome in 1938.
Read more about this topic: K-14 Process
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