E-6 process

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The E-6 process (often abbreviated to just E-6) is a Photographic processing system for developing Ektachrome, Fujichrome, and other color reversal (slide) photographic film.

Unlike some other color reversal processes (such as Kodachrome K-14) that produce positive transparencies, E-6 process can be done manually by amateurs with the same equipment that is used for processing black and white negative film or C-41 color negative film. However, unlike black and white developing, the process is very temperature sensitive; and the use of a tempered water bath to stabilize the temperature at 100 °F for the first developer and first wash is recommended to maintain process tolerances.

By contrast, the K-14 process and older Kodachrome processes are much more complex than E-6, and is currently performed in only one specialized processing plant world-wide (Dwaynes Photo Service in Parsons, Kansas); with all other Kodachrome cine and K-Lab processors shut down and decommissioned.

1 History
2 Six-bath compared to three-bath
3 Conventional six bath processing
4 See also
5 References
6 External links

[edit] History

E-6 generally replaced the E-3 and E-4 processes in 1976. The older E-3 process used light for reversal, and produced transparencies that faded more quickly. The E-4 process used chemicals that are environmentally unfriendly and the highly toxic reversal agent Tertiary Butyl-Amine Borane (TBAB).

[edit] Six-bath compared to three-bath

There are two families of E-6 processing chemistries. The original and standard that is used in commercial labs employs a six chemical bath process. The 'hobby' type chemistry kits (such as sold by Tetenal) use three chemical baths, combining the first developer and fogging bath solutions, and the pre-bleach, bleach and fixer bath solutions, with a discrete color developer step in between.^[1] However, the three step process suffers from poor process control (i.e. color shifts and color crossover), especially due to insufficient bleaching and/or fixing in the bleach-fixer ("blix") mixture.

[edit] Conventional six bath processing

The basic steps for developing color transparency films using process E6 are as follows.^[2]

First developer bath: 6:00 @ 100 °F/38 °C. This uses a potassium hydroquinone monosulfate - phenidone black & white film developer, with the preferred form of phenidone being 4-hydroxymethyl-4-methyl-1-phenyl-3-pyrazolidinone (13047-13-7). The first developer forms only a negative silver image in each layer of the film: No dye images are yet formed. The first developer is one of the most time and temperature critical steps in Process E-6, because it controls contrast.

First wash: Water stop bath, 2:00 @ 100 °F/38 °C. Originally this step used an acetic acid stop bath, but was replaced with a water-only bath for process economy, with concomitant slight adjustment downwards of first dev strength.

Reversal bath: Fogging bath, 2:00 @ 96-103 °F/36-39 °C. This bath prepares the film for the color developer step. In this bath, a chemical reversal agent is absorbed into the emulsion, with the chemical reaction instantly taking place. The reversal process can also be carried out using 800 footcandle-seconds (8.6 klx·s) of light, which is used by process engineers to troubleshoot reversal bath chemistry problems such as contamination, as well as issues of low tank turnover as process volumes decline.

Color developer bath: 6:00 @ 96-103 °F/36-39 °C. Process-to-completion step, which contains CD-3 developing agent as the main constituent. When film enters the color developer, the bath acts on the chemically exposed silver halide to form a positive silver image. (The metallic silver image formed in the first developer, which is a negative image, is not a part of the reaction that takes place in this step. What is being reacted in this stage is the "leftover" of the negative image, that is, a positive image.) As the color development progresses, metallic silver image is formed, but more importantly, the color developing agent is oxidised. Oxidised color developer molecules react with the color couplers to form color dyes in situ. That is, color dye is formed at the site of development in each of the three layers of the film. Each layer of the film contains different color couplers, which react with the same oxidised developer molecules but form different color dyes. Variation in color developer pH causes color shifts on the green-magenta axis with Kodak E100G & E100GX and Fujichrome films and on the yellow-blue axis with older Ektachrome films.^[3]

Pre-bleach bath: 2:00 @ 90-103 °F/32-39 °C. This bath was previously called "conditioner", but was re-named pre-bleach in the mid 1990's to reflect a major change in removing the formaldehyde from the process used in the final rinse. The pre-bleach bath solution has formaldehyde acting as a dye preservative and EDTA to "kick off" the bleach. The pre-bleach bath also relies on carry-over of the color developer (i.e. no wash step between the color dev and pre-bleach baths) to function properly; as well as carry-over from the pre-bleach to bleach baths.

Bleach bath: 6:00 @ 92-103 °F/33-39 °C. This is a process-to-completion step, and relies on carry-over of pre-bleach to "kick off" the bleach. The bleach converts metallic silver into silver bromide, which is converted to soluble silver compounds in the fixer. During bleaching, iron (III) EDTA is changed to iron (II) EDTA (Fe³⁺ EDTA + Ag⁺ + Br⁻→ Fe²⁺ EDTA + AgBr) before fixing. Kodak also has a recipe (process variant) which uses a higher concentration of bleach and a 4:00 bath time; but with process volumes declining this is uneconomical.

Wash step (optional): Rinses off the bleach and extends the life of the fixer bath. This wash step is recommended for rotary tube, sink line and other low volume processing.

Fixer bath: 4:00 @ 92-103 °F/33-39 °C. This is a process-to-completion step.

Second fixer stage (optional): Using fresh fixer. The archival properties of film and paper are greatly improved using a second fixing stage in a reverse cascade.^[4] Many C-41RA (rapid access) minilab processors also use 2 stage reverse cascade fixing for faster throughput.

Final wash: 4:00 @ 92-103 °F/33-39 °C.

Final rinse: 1:00 @ 80-103 °F/27-39 °C. Up until the mid 1990s, the final rinse was called a stabilizer bath, since it contained formaldehyde. Currently, the final rinse uses a Photo-Flo-style surfactant, and miconazole, an anti-fungal agent.

Drying: Drying in a dust-free environment.

[edit] See also

Replenishment

[edit] References

^ Rinses, washes, stop baths and stabilizer/final rinse (the final step of the process) are not counted in the counting of baths when describing both the conventional six bath and hobbyist three bath processes.
^ Process E-6 Using KODAK Chemicals, Process E-6 Publication Z-119. Kodak. Retrieved on 2007-07-04.
^ KODAK PROFESSIONAL EKTACHROME Films E100G and E100GX. Kodak. Retrieved on 2007-07-04.
^ Schwartz, Dan (March 8, 2004). Why two step fixing is a Really Good Thing. Photo.net. Retrieved on 2007-07-04. Note that this is the Photo.Net discussion thread of the 1998 technical paper by Dr. Michael J. Gudzinowicz.