Negative film sheet with lightproof back?

Discussion in 'Film and Processing' started by 10986431, Feb 26, 2020.

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  1. Hi all

    Just interested to know if theres any B&W sheet film that has a lightproof back. If not what could one do to ensure the back is lightproof?
     
  2. To my knowledge, their was no sheet film with a lightproof back. Kodachrome roll film was made with a REMJET backing (removable jet-black). This consisted of lampblack imbedded in binder called an acid-plastic. When Kodachrome was developed, the first chemical bath was a pre-hardener. This bath temperately hardened the film so it could withstand the rigors of a high-speed roller transport developing machine. This bath being alkaline, softened the acid-plastic. The film exited this tank and a soft spinning roller buffed its back-side to remove the REMJET. The purpose of this backing was to allow a spool of Kodachrome film to be handled in subdued light (motion picture film). This backing also prevented exposure from the rear. Many movie cameras leaked light through the viewfinder should the photographer remove his eye while filming This backing also served as an anti-halation coat preventing light from bright sources from traversing the film, hitting the pressure plate and reflecting back into the film from the rear.

    Common in that era was a film pack. This was a clever metal box that held 12 sheets. Each was protected by a thin opaque sheet of flexible paper. This was the same stuff used for the paper backing of roll film. Likely this is lamp-black coated on paper.
     
    Last edited: Feb 26, 2020
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  3. Sheet film is slightly less sensitive through the back, due to an incorporated anti-halation layer, but it's still light sensitive enough that you'll get an image if you load a darkslide the wrong way round.

    What are you trying to do? Because the simplest thing would be to use the film in a filmholder or double-darkslide - like it was meant to be used.
     
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  4. Here is my last film pack box. It didn't hold the film quite as flat as a sheet film holder, perhaps, but I never noticed any problem with it.

    I shot with it a lot. When you pulled out the paper tab to advance to the next film, I left it on to write notes on until I had entered the picture info in the log.
    Tri-X-film-pack.jpg
     
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  5. Wow this is so interesting, appreciate all the info here.

    What I am trying to do is make a DIY lightproof pocket for the film to remain outside the of light, so kind of my own double-darkslide I guess. This isn't for anything crazy just interested in what can be used for keeping light sensitive film safe. I was hoping to use something rather thin much like 120 backing paper, I just can't work out any product on the market thats thin and would allow for this, If I wanted to make my own DIY film for cameras I would love to include the lightproof backing paper. Anyone know of anything that could feasibly do this? Obviously I could recycle old 120 film backing paper but I want to try my own from scratch.

    Maybe its possible to paint the back of the film with something that would make it lightproof? How does a polaroid negative manage it or what material is 120 film using? Its all very interesting and I really want to play around with it to learn it more.

    Any help/ideas or useful links very much appreciated!
     
  6. Sheet film and photographic printing paper usually come in black polythene bags that are absolutely opaque - at least to visible light. Not sure if they completely block IR, and there might be a heating issue if left in direct sunlight.
    And that's not crazy?
     
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  7. Vincent Peri

    Vincent Peri Metairie, LA

    "This isn't for anything crazy........ If I wanted to make my own DIY film for cameras.."

    I'm an expert on crazy! I suffer from bipolar disorder (manic depression), and before I started taking medicine for it, I was certifiably nuts.

    Rodeo Joe is right... that IS crazy. But in a harmless way...
     
    Last edited: Feb 28, 2020
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  8. haha amazing thanks. Yes ok maybe a touch of crazy then hahaha!

    What about the paper used as backing paper? What could that be made from?
     
  9. Errrr, paper?
    What makes backing paper lightproof is the thick ink coating on it. It's possibly a plastic polymer layer these days, but it used to be just a heavily-pigmented ink.

    If you're thinking of going into competition with Ilford and Kodak, you've got a lot of catching up to do!
     
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  10. I seem to recall hearing/reading that Kodak and Ilford use the same supplier for backing paper, and don't actually manufacture it themselves. No idea how true that is, but if it is that supplier might be able to offer it in larger sizes. Of course, they'd probably also want a huge order of it.

    Anyone who shoots 120 film and develops themselves, or any lab that does 120, probably has piles of the stuff lying around. A roll of 120 film has about 5 feet of paper. A few pieces could conceivably be pieces together to test proof of concept.
     
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  11. Black construction paper?
     
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  12. First of all you've got to make something light sensitive, before worrying about how to protect it from light!
     
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