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  1. #21
    Photo Engineer's Avatar
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    Two methods are used. One is to use an undercut roller and have 1" of uncoated film on each edge. It is called selvedge. The other method used is air bearings. The paper runs on a curtain of air, suspended on a cushion of air. With this latter method, the film can turn corners of 45 to 90 degrees.

    PE

  2. #22

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    Historically, festoon loop dryers and spiral dryers have been used in the photo industry. I know DuPont used such dryers.

  3. #23
    AgX
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    Foma for example still have a festoon dryer.

  4. #24
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    And, EFKE used festoon drying until they closed the plant.

    PE

  5. #25

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    I have two coating questions (after reading Bob Shanebrook's book). 1) Why would one ever prefer a shiny overcoat vs matte? It is a really annoying characteristic of TMax films for example. 2) With a tabular grain emulsion, how do they get the flat grains oriented after the emulsion curtain pours onto the base? In a cross section of TMax, you can see the flat grains all lying pretty uniformly in the right orientation. I can't figure out how.

  6. #26
    Mustafa Umut Sarac's Avatar
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    With a tabular grain emulsion, how do they get the flat grains oriented after the emulsion curtain pours onto the base?
    I can think only ultrasonic treatment.

  7. #27
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    Here are the answers.

    1. Film used to be both glossy and matte. The matte was often on the back. It helped with retouching, but interfered with scanning. So, the matte was removed to facilitate scans and allow retouching in PS (<- gasp). However, gelatin is naturally rather glossy. The matte has to be added, and should not interfere with grain.

    2. T-grains lie flat naturally due to the settling or packing process as the gelatin dries. However, the gelatin must be flexible enough for the film to turn corners in MF cameras so that the gelatin does not crack and the t-grains do not crack. Either one can hurt the film image badly.

    PE

  8. #28
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    Great thread, I'm following this with interest.

    I have a bit of a long-winded question based on this point: in the world of B&W, the faster the film, the longer it is developed to realise the speed.

    So, to prevent overdevelopment of the slower, top (yellow) layer(s); is any kind of restrainer added to the emulsion for this layer? Or, do the bottom layers contain an enhancer to increase the speed (time) at which they develop? Either option would allow the layers to develop concomitantly to the same degree.

    My problem with this is that over time, the concentration of the restrainer/enhancer diffusing out of the emulsion and into the developer would increase, thus altering its performance (compensated for by replenishment, or chemical quenching by another developer additive?)

    Or, are the faster, lower layers deliberately under-developed and compensated for in other ways e.g. the chemistry of colour papers and/or the orange film mask?

    Or, is it too minor a problem to worry about in a 3:15 dev time and I'm over-thinking it?

    Note to self - need a copy of Bob's book...
    Last edited by Jim Taylor; 06-29-2013 at 07:10 PM. Click to view previous post history. Reason: Late at night, bad spelling!!
    Cheers,

    Jim.

  9. #29

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    Quote Originally Posted by Photo Engineer View Post
    Here are the answers.

    1. Film used to be both glossy and matte. The matte was often on the back. It helped with retouching, but interfered with scanning. So, the matte was removed to facilitate scans and allow retouching in PS (<- gasp). However, gelatin is naturally rather glossy. The matte has to be added, and should not interfere with grain.

    2. T-grains lie flat naturally due to the settling or packing process as the gelatin dries. However, the gelatin must be flexible enough for the film to turn corners in MF cameras so that the gelatin does not crack and the t-grains do not crack. Either one can hurt the film image badly.

    PE
    Wow, this is really surprising. I wouldn't have thought the individual grains would have enough mass relative to the viscosity of the gelatin to "settle" in a flat orientation. I figured they'd end up randomly oriented without some kind of intervention (not that I would have had the slightest idea how you'd do this other than the application of some type of "field").

    Regarding the overcoat sheen, are you saying we have digital to blame for TMax films having a shiny emulsion side??

    Ilford Delta (for example) has a matte emulsion side. Acros has a similar emulsion sheen to TMax.

  10. #30
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    Many answers to many questions. Yes, digital is partly to blame for the sheen, which does not bother me! Yes, the grains orient themselves in the direction of flow which is through the hopper, and thus they are parallel and flat!

    Jim, yes, there is a deveopability differential from top to bottom. Part of this is controlled by the Iodide and Bromide in the emulsion and part from both of these in the developer. That is why I have been so vocal in complaining about home brew C41 developers. If you get it wrong, you suffer consequences. There are several restrainers in each layer plus the DIR couplers which adjust development rate. The complete formula for Portra film is given in a patent, but OTOMH, I cannot remember the number nor the inventors. As one who worked on Gold 400, I can assure you that this question is not trivial and is at the forefront of our minds. You use ballasted restrainers and accelerants to achieve a proper rate so that all layers end up at the right point at the right time. This is why I avoid push or pull process. I over or under expose instead.

    This question also is the reason why I complain when someone says they can do C41 at 20C or some such. It just does not work right. BTDT!

    Maybe I should write Volume 2 of my book and include a complete workup of a color system!

    PE

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