View source for E-4 process

{{More citations needed|date=April 2021}}
:''See also [[Ektachrome]] for full details of Kodak E-series processes.''

The '''E-4 process''' is a now outdated process for developing [[transparency (photography)|color reversal (transparency)]] photographic film, which was introduced in 1966.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).{{efn|Not to be confused with [[tetra-n-butylammonium bromide]], which also is abbreviated as TBAB.}}<ref name=Jacobson80/>{{rp|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.<ref name=Talbert/> 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-dimethoxy[[tetrahydrofuran]],<ref name=Jacobson80/>{{rp|377, Formula 269}} which when mixed generates [[succinaldehyde]], a noxious gas which has been likened to tear gas.<ref name=Talbert/> Process E-6 films are hardened during manufacture, eliminating the prehardener step altogether and allowing them to be processed at {{cvt|100|F}}.

==Steps==
{{multiple image |align=right |direction=horizontal |title=Ektachrome film structure and exposure
 |image1=E-6 step 00.svg |caption1=Structure
 |image2=E-6 step 01.svg |caption2=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.<ref name=Z119-1>{{cite web |url=http://www.kodak.com/global/plugins/acrobat/en/service/Zmanuals/z119-1.pdf |title=Process E-6 Using KODAK Chemicals, Process E-6 Publication Z-119 {{!}} Chapter 1: Processing solutions and their effects |publisher=[[Kodak]] |archive-url=https://web.archive.org/web/20050825145808/http://kodak.com/global/plugins/acrobat/en/service/Zmanuals/z119-1.pdf |archive-date=August 25, 2005 |url-status=dead}}</ref>

The E-4 process is faster than E-3; whereas E-3 required 15 steps and up to 70 minutes from start to finish,<ref name=Talbert>{{cite web |url=https://www.photomemorabilia.co.uk/Colour_Darkroom/Early_Kodak_Ektachrome.html |title=Kodak Ektachrome Colour Transparency films |author=Talbert, Michael |website=Photo Memorabilia |access-date=24 August 2023}}</ref><ref name=E-13>{{cite book |url=https://archive.org/details/kodakektachromef00east/ |title=Kodak Ektachrome Film, Publication No. E-13 |date=1955 |publisher=Eastman Kodak Company |url-access=registration}}</ref>{{rp|30–31}} E-4 was completed in approximately 50 minutes over 13 steps.<ref name=PS-1968/> E-4 runs at {{cvt|85|F}},<ref name=PS-1968>{{Cite magazine | url=https://books.google.com/books?id=kyYDAAAAMBAJ&pg=PA130 |title = Kodak's new E-4 kit: 50-Minute Cure for People Afraid to Develop Their Own Color Film |author=Wahl, Paul |magazine=Popular Science |date = April 1968 |pages=130–131}}</ref> about 10&nbsp;°F (6&nbsp;°C) higher than E-3. The temperature tolerance is ±1&nbsp;°F for prehardener, ±{{frac|2}}°F for the first developer, and ±2–5&nbsp;°F for all other steps.<ref name=PS-1968/> 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 process]]es.<ref name=Talbert/><ref name=PS-1968/>

Total darkness is required during the first four development steps; normal room light can be used for the remaining steps.<ref name=PS-1968/>

{|class="wikitable" style="font-size:100%;text-align:left;"
|+E-4 Process<ref name=PS-1968/>
! colspan=3 | Step !! Schematic !! Time (min.) !! Temp. !! Description
|-
| rowspan=4 style="background:#000;" | &nbsp;
! 1 !! Prehardener
| rowspan=2 | &nbsp;
| 3 || {{cvt|85|F}} ±1&nbsp;°F
| Tempers film for high-temperature processing
|-
! 2 !! Neutralizer
| 1 || {{cvt|83–87|F}}
|
|-
! 3 !! First developer
| rowspan=3 | [[File:E-6 step 02.svg|frameless|upright=0.7]]
| 7 || {{cvt|85|F}} ±{{frac|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 || {{cvt|83–87|F}}
| Solution should not be reused for second stop bath (step 7)
|-
| rowspan=9 style="background:#fff;" | &nbsp;
! 5 !! Wash
| 4 || {{cvt|80–90|F}}
| Running water
|-
! 6 !! Color developer
| rowspan=3 | [[File:E-6 step 03.svg|frameless|upright=0.7]]
| 9 || {{cvt|83–87|F}}
|
|-
! 7 !! Second stop bath
| 3 || {{cvt|83–87|F}}
| Solution should not be reused from first stop bath (step 4)
|-
! 8 !! Wash
| 3 || {{cvt|80–90|F}}
| Running water
|-
! 9 !! Bleach
| rowspan=1 | [[File:E-6 step 04.svg|frameless|upright=0.7]]
| 5 || {{cvt|83–87|F}}
| Convert metallic silver to soluble particles
|-
! 10!! Fixer
| rowspan=4 | [[File:E-6 step 05.svg|frameless|upright=0.7]]
| 6 || {{cvt|83–87|F}}
| Dissolve silver particles, which can be recovered after processing
|-
! 11!! Wash
| 6 || {{cvt|80–90|F}}
| Running water
|-
! 12!! Stabilizer
| 1 || {{cvt|83–87|F}}
|
|-
! 13!! Dry
| var. || <{{cvt|110|F}}
|
|}

==History==
[[File:Kodak Ektachrome IE 135-20 Infrared Slide Film.jpg|thumb|right|Kodak Ektachrome Infrared film using E-4 process]]
E-4 processed film is color stable for about 30 years.<ref>{{Cite web | url=https://www.digitalrev.com/article/ektachrome-a-look-back | title=Ektachrome: A Look Back| date=25 January 2017}}</ref>

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 photography|infrared film]],<ref>{{cite magazine |url=https://books.google.com/books?id=_eMDAAAAMBAJ&pg=PA100 |title=Inner Visions |author=Ensanian, Armand |date=July 1988 |magazine=Popular Mechanics |pages=100–101 |access-date=24 August 2023 |quote=Color IR film has one drawback. It is not readily processed because it requires the old E-4 chemistry.}}</ref> 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.<ref>{{cite magazine |url=https://books.google.com/books?id=LxmeZrp-lukC&pg=PA114 |title=Pop Photo Snapshots: Bad and good news from Kodak |author=Rothschild, Norman |date=December 1985 |magazine=Popular Photography |pages=28–32;114 |access-date=24 August 2023 |quote=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.}}</ref> The E-4 chemicals were reverse-engineered and substitute formulae were published in the ''[[British Journal of Photography]] Annual'' in 1977.<ref name=Jacobson80>{{cite book |chapter-url=https://archive.org/details/DevelopingTheNegativeTechnique/page/n375/mode/2up |title=Developing: The Negative Technique |author1=Jacobson, Kurt I. |author2=Jacobson, Ralph Eric |date=1980 |edition=Eighteenth revised |publisher=Focal Press |location=London |isbn=0-240-44770-0 |access-date=24 August 2023 |chapter=Processing Colour Films |pages=363–383}}</ref>{{rp|374}}

==Notes==
{{notelist}}

== References ==
{{Reflist}}

== External links ==
* [http://www.kodak.com/global/en/professional/support/techPubs/cis111/cis111.jhtml Kodak specifications for hand mixing of chemistry]
* {{cite web |url=https://www.mat.uc.pt/~rps/photos/FAQ_e4.txt |title=More than you want to know about E-4 |date=19 May 1995}}

===Processing of older Ektachrome films (including Process E-4)===
* [http://www.filmrescue.com Film Rescue] USA and Canada
* [http://www.rockymountainfilm.com Rocky Mountain] USA

[[Category:Photographic film processes]]


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