How does peel apart work inside the camera

Discussion in 'Extreme, Retro, Instant and More' started by 10986431, Feb 28, 2020.

  1. Fascinated by polaroid and everything they did but completely intrigued by peel-apart film.

    Does anyone know how the paper in the camera works and how it comes together to make an image, maybe theres a video or diagrams out there? I understand the pressing of the film and the receiving paper and the pod part with the rollers but how does the film get pressed onto the receiving paper?

    Any insight super appreciated.


  2. AJG


    As you probably know, Polaroid pack and sheet film basically worked by making a negative and then transferring the remaining silver halides (with B&W materials) to the print. For most Polaroid materials the negative was lost, only the print remained. Type 55 (4x5) or 655 (3 1/4 x 4 1/4 pack film) did allow keeping the negative with some extra processing of the negative to preserve it. There is now a company making New 55 in ASA 100 and 400 4x5 sheet film if you're interested in trying it with a 4x5 camera and 545 Polaroid back.
    10986431 likes this.
  3. You may find interesting U.S. patents 2,543,181; 2,662,822; 2,603,565 and 2,647,056.

    The basic process relies on the theory of diffusion transfer reversal which was discovered by Andre Rott in the 1930s. Basically, if you take a wet, developing piece of film and press it against a specially treated piece of paper, you can get a positive print on the paper without an enlarger or any light source. This is because unexposed silver halide from the negative becomes soluble, transfers through the developer and lands on the receptor sheet, where it is reduced to metallic silver forming a positive image.

    Now, if you look at either Polaroid pack film or roll film (the two are the same in chemistry but different in dimensions) you have three key components. You have a negative, you have a developing pod containing reagent, and you have a receptor sheet.

    The negative is simple, it is like any other and through the life of Polaroid materials some common emulsions such as Kodak's Panatomic-X and Verichrome were used. Now, since no light needs to be shone through the negative to make a print, the negative was often simplified by coating the emulsion onto a paper backing, rather than something transparent like cellulose acetate. On film where the negative is recoverable, there is either a peelable lightproof backing on the rear of the negative, or like Fuji used with their instant packfilms, a black carbon layer applied to the back of the transparent negative to lightproof it.

    The reagent is also relatively simple, the base component is a monobath, containing both a developing agent and a fixer so that the print can develop and then be fixed so as not to be sensitive to light. Added to this is a gelling agent, normally carboxymethylcellulose, which makes this developing combination a viscous jelly, able to be used in a camera without flowing everywhere. Most Polaroid developing reagents contained chemicals to stabilize the chemical reactions over a wider range of temperatures, so that air temperature had less of an effect on the development time of the print.

    The third component is the receptor sheet, this is a piece of paper chemically treated to receive silver halide from the negative. The way it is treated varied. Polaroid treated their receptor sheets with some form of metallic sulfide, while Fuji uses organic polymers to increase nucleation.

    There is also normally a frame included in separable instant films between the receptor and negative sheets which both frames off the area of the receptor sheet which gets coated with reagent to create a neat border on the finished print, and also ensures a gap between the negative and receptor sheets to ensure all of the reagent does not get spread too thin and squished out the sides.

    Now, Scott, from what I gather from your recent postings, I surmise that you may have some interest in making your own instant film. As somebody who has also gone down that train of thought, I will tell you that the receptor sheet is going to be the most difficult component to source. Negative stocks are readily available, and developing reagents can be mixed from off the shelf components, but sourcing or making a receptor sheet would likely be the most difficult part of the process. The reason being that we don't know exactly what they were treated with. The late Ron Mowrey over on the Photrio forums was able to surmise that some type of metallic sulfide was used, but beyond that we don't know. If you look at one of the patents above, it gives a great number of coatings that may work for the receptor sheet, but does not state what is ideal or which one Polaroid ultimately used. Remember, the purpose of patents is to describe every possible way of doing something, not to explain how to do it.

    Regardless of what your intentions are, I wish you luck in your endeavors.
    10986431 likes this.
  4. haha hey. Hunter_Compton you are absolutely right, it may fail it mayor end up messy and it will possibly be a huge waste of time but I am very much up for giving it a whirl. I shall keep you all posted on how far I get. If you have any info/advice or anything like that please do let me know.
  5. I am not sure which question you are asking about. The chemistry has been discussed before and here,
    but one that I still wonder about, and maybe what you are asking about, is how the chemicals get spread
    the right way, and not the wrong way.

    I was recently using a Fuji Instax camera with 8 year old film, which works well after cleaning
    the rollers, but I did notice that the chemicals don't get all the way to the corners. It is very close,
    maybe a mm from the corner.

    Many have a ridge on one roller, so when pressed with springs they have an appropriate sized
    gap so as not to over or under squeeze the film. There is a paper frame that you peel the print
    off of that, hopefully, keeps the chemicals from going out the side.

    At the end, there are rubbery wedges that increase the roller spacing, so that there is room for the
    chemicals at the end, without going out the end. But often enough, chemicals go where they aren't
    supposed to go. That is why it is so often necessary to clean the rollers.

    For the pack cameras, and I believe the roll cameras, it is possible to open the back and
    get the rollers out without exposing the film.
    10986431 likes this.
  6. How you clean the rollers in Instax cameras?
  7. It took me a few tries to figure out a good way, but I think in the end I used isopropanol.

    There is a piece of plastic around the spot where the print comes out, which you remove,
    and then they are fairly visible. I might have even tried it with batteries and press the
    shutter release, in which case it spins the rollers to eject the print. Put a soaked
    paper towel against them at that time. I didn't figure out how to remove them.
    eugen_mezei likes this.

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