See also Ektachrome for full details of Kodak E-series processes.
The E-4 process is a now outdated process for developing color reversal (transparency) photographic film, which was introduced in 1966.
The process is infamous for two reasons:
First, it uses the highly toxic boron hydride-based reversal agent tertiary butyl-amine borane (TBAB). Early releases of the consumer-sized version of the chemistry provided the TBAB in the form of a tablet, possibly to avoid the possibility of inhalation. This was later changed to loose powder, likely as a countermeasure against inadvertent ingestion of the substance.
Second, the prehardener agent contains formaldehyde and 2,5-dimethoxytetrahydrofuran, which when mixed generates succinaldehyde, a noxious gas which has been likened to tear gas. Process E-6 films are hardened during manufacture, eliminating the prehardener step altogether and allowing them to be processed at .
Ektachrome film has three separate light-sensitive layers; each layer is sensitive to a different group of wavelengths corresponding to red, green, and blue colors. When the film is exposed, each layer records a latent image based on its sensitivity. A yellow filter prevents blue light from exposing the green- and red-sensitive layers, which have some sensitivity to blue light.[1]
The E-4 process is faster than E-3; whereas E-3 required 15 steps and up to 70 minutes from start to finish,[2] [3] E-4 was completed in approximately 50 minutes over 13 steps. E-4 runs at,[4] about 10°F (6°C) higher than E-3. The temperature tolerance is ±1°F for prehardener, ±°F for the first developer, and ±2–5°F for all other steps.[4] The ME-4 process was a motion picture variation of the E-4 process.
The major change for E-4 was the inclusion of a chemical reversal agent, which permits processing of the film without the manual re-exposure/fogging step required by the predecessor E-1 / E-2 / E-3 processes.[2] [4]
Total darkness is required during the first four development steps; normal room light can be used for the remaining steps.[4]
| 1 | Prehardener | 3 | ±1°F | Tempers film for high-temperature processing | ||
|---|---|---|---|---|---|---|
| 2 | Neutralizer | 1 | ||||
| 3 | First developer | 7 | ±°F | Conventional black-and-white developer used to transform silver halide crystals exposed in all three layers as a negative image. | ||
| 4 | First stop bath | 2 | Solution should not be reused for second stop bath (step 7) | |||
| 5 | Wash | 4 | Running water | |||
| 6 | Color developer | 9 | ||||
| 7 | Second stop bath | 3 | Solution should not be reused from first stop bath (step 4) | |||
| 8 | Wash | 3 | Running water | |||
| 9 | Bleach | 5 | Convert metallic silver to soluble particles | |||
| 10 | Fixer | 6 | Dissolve silver particles, which can be recovered after processing | |||
| 11 | Wash | 6 | Running water | |||
| 12 | Stabilizer | 1 | ||||
| 13 | Dry | var. | < |
E-4 processed film is color stable for about 30 years.[5]
The process largely was phased out in 1976 with the introduction of the E-6 process, which is more environmentally friendly due to its lack of toxic chemicals. E-6 avoids the use of TBAB by adding a separate reversal bath containing the tin salt stannous chloride.
The E-4 process has been discontinued since 1996; after 1976 it was used solely for Kodak IE color infrared film,[6] due to a legal commitment by Kodak to provide process support for 30 years after introduction. Kodak discontinued E-4 processing in 1985, but independent photofinishers continued to support the process.[7] The E-4 chemicals were reverse-engineered and substitute formulae were published in the British Journal of Photography Annual in 1977.[8]