Puzzled about Kodachrome processing

Discussion in 'Color: Film, Paper, and Chemistry' started by Fredrik Sandstrom, Nov 4, 2010.

  1. Fredrik Sandstrom

    Fredrik Sandstrom Member

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    Here's a question for PE or anyone else who understands the K-14 process - there's one thing that's puzzling me:

    Since the first (B&W) development is obviously not taken to completion, there must be developable silver halide left in all layers after that step. So, after the red re-exposure, in the cyan development stage, how come cyan dye is only formed in the bottom (red-sensitive) layer, and not in the two others?
     
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  2. railwayman3

    railwayman3 Member

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    Presumably because only the bottom layer is sensitive to red light? (Which is perhaps why 3 separate re-exposures (or chemical fogging for the final layer) are needed?). With E6, there is just one re-exposure or fogging stage (in older reversal processes, color or B&W, this was, of course,, done with exposure to a white light).

    I'm sure it's more complicated than that, so look forward to responses from PE and others more expert than I. :smile:
     
  3. Fredrik Sandstrom

    Fredrik Sandstrom Member

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    No no, I'm talking about the little bit of silver halide in the blue and green sensitive layers that is already developable, regardless of any red re-exposure. Why is cyan dye not formed there? Or perhaps it is, but it's compensated for in some way..?
     
  4. railwayman3

    railwayman3 Member

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    I understand what you are saying, and the potential problem of developable halide in the "wrong" layers.

    There is a Wikipedia entry on K-14 processing,
    ( http://en.wikipedia.org/wiki/K-14_process ), which states:
    "First Developer -
    All (my italics) exposed silver halide crystals are developed to metallic silver via a PQ developer."

    This seems to indicate that first development is therefore carried to completion? (The Wiki article is quite interesting, would be useful if PE or our other experts have any comments as to its accuracy.)
     
  5. Fredrik Sandstrom

    Fredrik Sandstrom Member

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    Interesting. How, if that is indeed the case, is push-processing (which is offered for K-14) carried out? Increased time in the first developer (which I thought was the way) would make no difference... :confused:
     
  6. railwayman3

    railwayman3 Member

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    I'm not sure of ther answer, but maybe the "development to completion" is for a correctly dense "negative" image to be produced from a film exposed at box speed, i.e. a correct scale of tones, with a highlight almost fully exposing the halide.
    For push-processing, an image taken at a higher film speed setting (less exposure) would then appear underexposed if the first developer were used for the standard time. Increased development in the first developer would bring such an image to a correct scale of tones, so that effectively the film speed was increased.

    I don't think that "development to completion" means that more time in the developer would have no further effect, only that development is completed to produce a correct range of tones on a "correctly exposed" picture? Remember that, if we push-process a B&W film, a negative exposed at the box speed will become too dark, i.e. "over-exposed".
     
  7. Fredrik Sandstrom

    Fredrik Sandstrom Member

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    Hmm. If all exposed silver halide has been converted to silver (as the Wikipedia article implies) I don't see what more time in the developer could possibly accomplish. Please enlighten me if this is a misconception!

    If there is (as I still believe must be the case) some amount of developable silver halide in all layers after the first developer, it seems to me this must turn into a very thin cyan colored negative image in the cyan development step. If this is somehow prevented, I'd be curious to understand how. :cool:
     
  8. Q.G.

    Q.G. Inactive

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    The first developer produces a negative image, leaving a positive 'image' in unexposed and undevelopable (if you don't leave it in the developer for too long) in silver halide.

    The next steps gives a selective colour exposure to the three layers, with development after each exposure only forming dye in the layer that is made developable by the selective colour exposure.
     
  9. Fredrik Sandstrom

    Fredrik Sandstrom Member

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    Yes, but what about the exposed and developable halide that the first developer leaves behind when it does not go to completion? That's what I'm asking about.

    Yes, that's the very basic principle by which Kodachrome works. I'm familiar with all that. My initial question remains. :sideways:
     
  10. railwayman3

    railwayman3 Member

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    As I said in the previous post, I'm sure that "completion" in this context means the production of a negative with a balanced set of tones for a scene correctly exposed at the box speed of the film. I don't think that this necessarily infers that there is exposed and developable halide left at that point?

    If a shot is nominally "underexposed" (i.e. exposed at a higher film speed rating), normal development will not give a full range of tones. So, as with any push-processing, we develop longer to give a more dense silver image, i.e. the nucleus of exposed halide is "developed" to produce more silver.

    I agree that there still seems to be some weakness in that explanation....paging PE to help us out here? :smile:
     
  11. tiberiustibz

    tiberiustibz Member

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    So the first development develops almost all of the exposed halide. The red re-exposure exposes all the red sensitive halide which is developed in cyan developer. The blue re-exposure exposes only the uppermost layer because directly below it is a yellow filter layer, which is developed in yellow developer. The rest is chemically fogged and developed in magenta.

    To answer your question, there will always be color crossover where dyes are developed in incorrect layers. The goal of good K14 processing is to minimize that effect.
     
  12. Photo Engineer

    Photo Engineer Subscriber

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    First development goes to completion and then some due to its being a solvent developer. This leaves just the right amount of "positive" silver left to image correctly.

    The red layer on the bottom is exposed through the base to very narrow cutting red light exposing only the red layer and then all of the red sensitive Silver Halide is developed. Then the blue sensitive layer is exposed through the top and the blue sensitive Silver halide is developed. The yellow filter layer protects the green sensitive layer from light reexposure. Finally, the film is fogged chemically and the film is developed in the final developer.

    Throughout this, scavengers and competers are present to prevent color formation in the wrong layers just in case.

    PE
     
  13. railwayman3

    railwayman3 Member

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    Thanks for that explanation. However, if "normal" development is carried out to completion, how, then, is "push-processing" of Kodachrome done?
     
  14. Photo Engineer

    Photo Engineer Subscriber

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    The silver halide solvent dissolves and redeposits more silver on the negative image and the negative image also goes into fog. This brings the Dmin of the negative up and thus the Dmax of the positive comes down. So, in the final slide the blacks can be gray if the push is strong enough. Also, contrast and color saturation change.

    As the Dmax of the positive decreases, the overall impression is that the image becomes lighter (pushed) when what is really being accomplished is just Dmax reduction. There is no real gain in speed, just an apparent change in the mid tones.

    PE
     
  15. railwayman3

    railwayman3 Member

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    That's interesting, thank you...I think I understand. :smile: It seem quite different to pushing B&W negative film.

    It all just confirms what a remarkable process Kodachrome is...I admire the people who thought it out and improved it over the years.
     
  16. Steve Roberts

    Steve Roberts Member

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    Not actually directly concerned with this thread, but on the rare occasions that I try to start a new thread rather than reply to an existing one, I ALWAYS have trouble working out how to start a new thread and on this occasion have given up! Could there not be a button in the header bar that says "Start New Thread"?

    Anyway, I spent part of the weekend just gone shooting my last roll of Kodachrome. I agonised for some time what should be the contents of The Last Roll, but eventually decided that I'd just go out and shoot the kind of subjects that I typically did in the days when I used Kodachrome exclusively (which actually much the same old stuff that I shoot now!). Thus I took myself off to Cornwall and shot a good many mining remains. In doing so, I found myself thinking about the deadline for getting the film to Switzerland for onward shipment to Dwayne's. I couldn't help wondering, as the Day of Reckoning approaches, surely Dwayne's is going to be snowed under with work. Can anyone 'in the know' say whether Dwayne's are gearing up for this influx of work? I imagine that there could conceivably be a large number of disappointed people who may have sent films in good time but don't get them back processed.

    Apologies if this has already been discussed (it probably has) but there's so much Kodachrome correspondence to search through here!

    Best wishes,

    Steve
     
  17. Fredrik Sandstrom

    Fredrik Sandstrom Member

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    Thank you PE for your explanation, it makes sense!

    How about pull processing? I once shot a roll of K64 at EI 32 and had it pulled one stop. I was disappointed that there was a slight cyan cast to the images. I didn't ponder the actual reason for it then, but I now realize it is indeed consistent with my theory that leftover developable halide after the first developer results in a thin cyan colored negative image in all layers later. Is this what happened to me, or is there another reason behind the color cast?
     
  18. railwayman3

    railwayman3 Member

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    I've no inside knowledge at all, but FWIW I'd guess that there might not be any significant last-minute-rush. I'd think that most Kodachrome this year has probably been shot by enthusiasts like ourselves, who have planned their photography throughout the seasons and have been well aware of the final processing date. My own Kodachrome shooting should be completed in the next couple of weeks, in time to get the film to Lausanne before the 30th, and I should then have very little film left....if I do have a couple left over in December, I won't be too worried. I'd rather keep them in honourable retirement as museum pieces, rather than deliberately waste them on rubbish shots. :smile:

    To be fair, Kodak have handled the end of European film as well as could be expected, and I'm sure that they and Dwaynes will honour the final dates for receipt of film, even if they have to run the processing line for a day-or-two into January.
     
  19. Photo Engineer

    Photo Engineer Subscriber

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    Pull processing underdevelops in the first developer giving a weaker negative image. This leaves more Silver Halide to form dyes in the color developers. Since development is diffusion related, I suspect that the cyan (bottom) layer was the most weakly developed and therefore in the reversal process formed more dye giving a cyan cast. By this same reasoning, a push would tend to give warm images.

    PE
     
  20. MattKing

    MattKing Subscriber

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    Steve:

    You need to be in the "list of threads in a forum" area to start a new thread, not in a thread that is part of the forum.

    Click on the forum title near the top of the screen and it will take you to that forums list of threads. Then, again near the top of the page you will see a grey box that contains the words "+POST NEW THREAD". Click on that box, and you are off!

    You can also get to each forum individually by clicking on the "Forum" tab at the top of the screen, moving through the list of forum headings, and then clicking on the forum title itself.

    As to your question - I expect Dwayne's has a certain amount of chemistry on hand, but that Kodak has most likely committed to provide whatever additional chemistry will be required to develop all Kodachrome in Dwayne's hands as of close of business on December 30th.
     
  21. Steve Roberts

    Steve Roberts Member

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    Thanks Matt. I'll print your instructions for future reference!
    Best wishes,
    Steve
     
  22. Diapositivo

    Diapositivo Subscriber

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    If I remember well what I read, Dwayne and Kodak basically state that they will not process film which will arrive after the deadline. They don't say that Kodachrome processing will cease the day of the deadline.

    When I read it I interpreted it as if they were guaranteeing processing for every film which reached the laboratory within the deadline (even if they did not use the word "guarantee" probably). I would not be surprised if processing activity will be prolonged for a couple weeks or more to work all the film arrived within the deadline. This is process prepaid material, nobody is going to be economically hurt even if processing had to go on for months.

    Fabrizio
     
  23. Sirius Glass

    Sirius Glass Subscriber

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    The deadline is that Dwayne's receives it by 30 December 2010.

    Steve
     
  24. msa

    msa Member

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    I've been batching my remaining Kodachrome directly to Dwayne's, 6 rolls at a time.

    The last shipment arrived last week, and they turned it around in two days from receipt based on the tracking information both ways.

    If there's a rush, it's not visibly slowing them down any.