E-6 process

The E-6 process is a process for developing color reversal film.

The essential elements of the process are:

1. first developer, which is chemically similar to standard black and white developers
2. color developer, which contains a chemical reversal agent together with a developer
3. bleach-fix, containing both a thiosulphate fixer and a bleaching agent to remove unused dyes
4. wash, in water
5. formaldehyde stabilizer

Variations exist. The color developer and reversal are sometimes performed in two steps. Some early versions separated the bleach and fix steps.

Ordinarily, the process is conducted at 100° F. Total process time is about 30 minutes. Shorter process times can be achieved at higher temperatures.

Recent versions of the process have replaced the stabilizer with a film conditioner, and incorporated a chemically different stabilizer into the color developer. This was done out of concern for the health effects of the formaldehyde on lab workers.

Process E-6 is the most demanding photofinishing process in widespread use. It has more steps than the C-41 process used for color negatives. There is little processing lattitude because there is no opportunity to correct density or color balance when printing.

It replaced the E-3 process in the late 1960s. The E-3 process used light for reversal, and produced transparencies that faded more quickly with repeated projection or the passage of years.

The K-12 and older Kodachrome processes are more involved than the E-6 process, and are performed only in specialized plants. Each of the three film layers is developed separately, and dyes are added during the process rather than being incorporated in the film base.