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The E-4 process is a now outdated process for developing color reversal (transparency) photographic film, which was introduced in 1966.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).[a][1]: 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.[2] 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,[1]: 377, Formula 269  which when mixed generates succinaldehyde, a noxious gas which has been likened to tear gas.[2] 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.[3]

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][4]: 30–31  E-4 was completed in approximately 50 minutes over 13 steps.[5] E-4 runs at 85 °F (29 °C),[5] 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.[5] 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][5]

Total darkness is required during the first four development steps; normal room light can be used for the remaining steps.[5]

E-4 Process[5]

Step			Schematic	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

Kodak Ektachrome Infrared film using E-4 process

E-4 processed film is color stable for about 30 years.[6]

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,[7] 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.[8] The E-4 chemicals were reverse-engineered and substitute formulae were published in the British Journal of Photography Annual in 1977.[1]: 374 

Notes

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

References

1. 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.
2. Talbert, Michael. "Kodak Ektachrome Colour Transparency films". Photo Memorabilia. Retrieved 24 August 2023.
3. "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.
4. Kodak Ektachrome Film, Publication No. E-13. Eastman Kodak Company. 1955.
5. 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.
6. "Ektachrome: A Look Back". 25 January 2017.
7. 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.
8. 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.

External links

• Kodak specifications for hand mixing of chemistry
• "More than you want to know about E-4". 19 May 1995.

Processing of older Ektachrome films (including Process E-4)

• Film Rescue USA and Canada
• Rocky Mountain USA