E-4 process

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The E-4 process is a now outdated process for developing color reversal (transparency) photographic film, which was introduced in 1966.

Drawbacks

The process is infamous for two reasons:

First, it uses the highly toxic boron hydride-based reversal agent tertiary butyl-amine borane (TBAB).^{: 379, Table LXVI} 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,^{: 377, Formula 269} 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 100 °F (38 °C).

Steps

Ektachrome film structure and exposure

Structure

Sample exposure to various colors

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.

The E-4 process is faster than E-3; whereas E-3 required 15 steps and up to 70 minutes from start to finish,^: 30–31 E-4 was completed in approximately 50 minutes over 13 steps. E-4 runs at 85 °F (29 °C), about 10 °F (6 °C) higher than E-3. The temperature tolerance is ±1 °F for prehardener, ±1⁄2°F for the first developer, and ±2–5 °F for all other steps. 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.

Total darkness is required during the first four development steps; normal room light can be used for the remaining steps.

E-4 Process
		Time (min.)	Temp.	Description
1	Prehardener	3	85 °F (29 °C) ±1 °F	Tempers film for high-temperature processing
2	Neutralizer	1	83–87 °F (28–31 °C)
3	First developer	7	85 °F (29 °C) ±1⁄2°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	83–87 °F (28–31 °C)	Solution should not be reused for second stop bath (step 7)
5	Wash	4	80–90 °F (27–32 °C)	Running water
6	Color developer	9	83–87 °F (28–31 °C)
7	Second stop bath	3	83–87 °F (28–31 °C)	Solution should not be reused from first stop bath (step 4)
8	Wash	3	80–90 °F (27–32 °C)	Running water
9	Bleach	5	83–87 °F (28–31 °C)	Convert metallic silver to soluble particles
10	Fixer	6	83–87 °F (28–31 °C)	Dissolve silver particles, which can be recovered after processing
11	Wash	6	80–90 °F (27–32 °C)	Running water
12	Stabilizer	1	83–87 °F (28–31 °C)
13	Dry	var.	<110 °F (43 °C)

History

E-4 processed film is color stable for about 30 years.

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, 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. The E-4 chemicals were reverse-engineered and substitute formulae were published in the British Journal of Photography Annual in 1977.^: 374

Notes

↑ Not to be confused with tetra-n-butylammonium bromide, which also is abbreviated as TBAB.

References

1 2 3 Jacobson, Kurt I.; Jacobson, Ralph Eric (1980). "Processing Colour Films". Developing: The Negative Technique (Eighteenth revised ed.). London: Focal Press. pp. 363–383. ISBN 0-240-44770-0. Retrieved 24 August 2023.
1 2 3 4 Talbert, Michael. "Kodak Ektachrome Colour Transparency films". Photo Memorabilia. Retrieved 24 August 2023.
↑ "Process E-6 Using KODAK Chemicals, Process E-6 Publication Z-119 | Chapter 1: Processing solutions and their effects" (PDF). Kodak. Archived from the original (PDF) on August 25, 2005.
↑ Kodak Ektachrome Film, Publication No. E-13. Eastman Kodak Company. 1955.
1 2 3 4 5 6 Wahl, Paul (April 1968). "Kodak's new E-4 kit: 50-Minute Cure for People Afraid to Develop Their Own Color Film". Popular Science. pp. 130–131.
↑ "Ektachrome: A Look Back". 25 January 2017.
↑ Ensanian, Armand (July 1988). "Inner Visions". Popular Mechanics. pp. 100–101. Retrieved 24 August 2023. Color IR film has one drawback. It is not readily processed because it requires the old E-4 chemistry.
↑ Rothschild, Norman (December 1985). "Pop Photo Snapshots: Bad and good news from Kodak". Popular Photography. pp. 28–32, 114. Retrieved 24 August 2023. Eastman Kodak no longer offers processing for E-4 films such as Ektachrome Infrared and Kodak Microphotography color-slide films. However, there are more than a dozen independent labs in the U.S. that offer this service.