Cross Processing E6 to C41 - what goes on?

Discussion in 'Color: Film, Paper, and Chemistry' started by Bohngy, Jun 7, 2009.

  1. Bohngy

    Bohngy Member

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    Dear all, just a "what happens" question really...
    You'll have to forgive my ignorance/stupidity (substitute where applicable) but what exactly happens when you process E6 as C41?

    As I understood it, E6 is dye-based whereas C41 is silver based (albeit on 3-layers). What I can't understand is how you can develop the silver in an E6 film when it wasn't there in the first place.

    Just something I've always thought of, but never been brave enough to ask!

    thanks.
     
  2. Q.G.

    Q.G. Inactive

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    It is 'there' in E6 film too.
    :wink:
     
  3. Bohngy

    Bohngy Member

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    ok... care to elaborate a bit? thanks
     
  4. yellowcat

    yellowcat Member

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    Both E6 and C41 films use silver that is removed in processing to leave a dye image.

    And the "in three layers" is out of date, almost all colour films contain multiple layers sensitive to each colour.
    Each of these layers has different speed and contrast characteristics.

    There are other layers as well that are not sensitive to light.
    Such as anti-scratch coatings , filter layers and anti-halation layer.

    Each emulsion layer contains in addition to the light-sensitive silver halide chemicals called dye couplers.

    These chemicals are located in the blue, green and red-sensitive layers and produce yellow, magenta and cyan dyes, respectively, when developed in colour developer.
     
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  5. Q.G.

    Q.G. Inactive

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    The difference is that in E6 films, after developing the silver image (which produces a negative, just like in colour negative film), it is bleached out.
    After that, the remaining, unexposed 'silver' is made developable, producing the positive image.
    In colour negative film only the exposed silver is developed, producing the negative image.

    For the rest, both processes are basically the same.
     
  6. railwayman3

    railwayman3 Member

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    Broadly speaking, E6 and C41 films are similar in structure, with the silver compounds necessary for the light-sensitivity, and the final images on the film being in dye only. If they were not so similar, cross-processing would not be possible.
    There are lots of detailed differences, of course, but it's basically the type of processing which gives a positive or negative. (Just as you can produce a B&W transparency from a standard "B&W" negative film, by "reversal processing" as described above by Q.G.)
     
  7. Mike Wilde

    Mike Wilde Member

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    Here is my take on colour formation and how they come into play in cross processing. I am not a chemical engineer, so some of the ideas are not going to be technically spot on.

    Modern colour films are technically known as integral tripack films (I know that there are more than three layers in the film- I am just talking a basic idea here) have three light sensitive layers in them. They have what are called colour formers in each layer. (Kodachrome does not - the colour formers are introduced during processing with the K-14 process.)

    Light strikes the film, to effectively cause three different silver latent images, one in each colour sensitive layer, to form when the image forming exposure is made in the camera. The film is then developed. The developer is a PPD- salt type developer. The salts are complex organic compounds.

    When the silver in each layer is 'developed' the developer is oxidised, proportional to the amount of light that struck that particular area. The 'salt' part of the compound is released proportional to the amount of PPD developing agent oxidised. Guess what - that salt, when it is unbound, bumps into the colour formers laying around. The colour former and oxidised salt combine to make a visible dye.

    The colour formers in each layer are set up to give the three colours (this is a simplification of a very complex issue), all while react with the same salt compound in a particular developer.

    Cross processing exploits that E-6 (slides) use a colour developer that is short handedly referred to as CD-3. C-41 (negatives) use a developer referred to as CD-4. There has been a CD-1 (now obsolete), and I think that there is a CD-2 used in movie film.

    When you develop E-6 with CD-4 the dyes formed are not a 'designed as normal' response, but you get a distorted colur palette as an end result that many find artistically agreeable.

    After the colour developer and stop bath steps the un-coupled dye formers, and exposed silver is 'bleached' away, and then any unexposed silver left in the film is fixed away.

    For c-41 some processes combine the bleach and fix into a common 'blix', whille others use a separate bleach and fix.

    Better E6 processes almost always use separate bleach and fix baths. For positive transparencies, there are up front steps of first developer, a black and white developer, and then a chemical reversal to chemically expose all of the sliver that was not developed by the first developer.

    C-41 film has an orange mask in the film base, to deal with less than perfect dye solutions that occur when trying to make a true un-masked reversal with the available dye couplers and colour developer reactions. Early colour negative films did not have such a mask.

    Ron - fee free to hop in and set me straight if any of these generalities are likely to lead others astray.
     
  8. Photo Engineer

    Photo Engineer Subscriber

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    A lot of what went on above is incorrect or distorted. Sorry guys. Mike is closer than anyone.

    All color films except Kodachrome contain couplers which react with oxidized color developer to give a color image. In C-41 films this is simply a Develop - bleach - fix - stabilize process (washes omitted for clarity), just like B&W to give a negative image directly from the silver halide that was exposed.

    In E6 films, the sequence is B&W develop - re-expose or fog - color develop - bleach - fix - stabilized (again omitting washes and other ancillary steps). This gives a negative silver halide image that is retained, unlike in some descriptions above, until the end of the color develop stage.

    Now, here is the catch. Color negative films are optimized for printing and have a low contrast and are "coupler starved" to give sharp images and low contrast. Color reversal films are "coupler rich" and are designed to directly give high contrast and saturated images. Therefore E6 films in C41 give high contrast images unintended for good prints. Kodak recommends adding about 2 g/l of Citrazinic acid, a contrast reducer, to the C41 developer to improve this.

    But the problem is compounded by the fact that C41 films use CD4 and E6 films use CD3. The difference in activity causes crossover and the difference in the dye formed causes dye hue problems.

    So, if you understand all of the above, and like to live with the images, you can get some very unusual and odd effects from cross processing either way. I have done both and they can really knock your socks off. The biggest cross process result regarding beauty is when you do some EIR in C41. You can get "normal" color with inverted tones! This can be truly spectacular.

    It is fun to do and has been used since early days. The cover on Life magazine of Alan Sheppard was done with cross processed HS Ektarchrome in C-22. It gave wonderful results pushed to ISO 400.

    PE
     
  9. Emulsion

    Emulsion Member

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  10. mellowscintilla

    mellowscintilla Member

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    a, slightly confused regarding this matter. does processing e6 in c41 chemicals still produce a reversal, albeit colour-shifted, image, or does it produce a negative image?

    similarly, does processing c41 negative stock in E6 chemicals result in a reversal image, again albeeit with a colour change, or does it still result in a negative?
     
  11. Photo Engineer

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    E6 films in C41 gives a high contrast negative image on an Ektachrome or Fujichrome film. These can give some pretty interesting results.

    C41 films in E6 give an orange colored, low contrast positive image. These results are pretty useless IMHO.

    PE
     
  12. Neanderman

    Neanderman Member

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    So what if you used the E6 color developer first, on E6 film, then bleached and fixed?

    Ed
     
  13. Photo Engineer

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    Ed;

    You would get a very very foggy, off color negative. The E6 color developer is designed to go to completion and therefore will fog a film if used as the direct first and only development step of any process.

    PE