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  1. #1
    BetterSense's Avatar
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    Cellulose Acetate vs. Polyester film base

    I hope this fits here.

    I was aware that film switch from nitrate to 'safety film' around the 50s. But I thought it was still made of cellulose acetate, even today. Apparently it's now Polyester or PET film? When did this transition occur, and do you think there was any difference in the look the film produced?

  2. #2
    AgX
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    Films for pictorial still photograph typically have a TAC base.

    Those with a PET base either are converted from stock intended for `industrial´use (aerial, surveilllance), or are those few where the advantages of PET have been considered. Furthermore the very situation at a manufacturer has its impact on the choice of base too.

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    Dimensional changes in film during processing hurts image size and shape, so PET film is used for graphics arts films and many LF films where dimensional shrinking or expanding can be noticable with TAC. All dye transfer materials were made on PET support.

    Also, the change to safety film took place a bit before the 50s. I have seen safety film on films at least 10 years earlier or more.

    PE

  4. #4
    Michel Hardy-Vallée's Avatar
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    Here's the story of film base how I know it:

    Professional films were often coated on cellulose nitrate, which is the nasty, inflamable and almost unextinguishable stuff. At the same time, amateur films were coated on cellulose diacetate. Diacetate did not have the flammability problems of nitrate, but was more susceptible to turn into acetic acid ("vinagering").

    There was something about nitrate that made it better than diacetate, hence the pro use, but I don't know what.

    Then, cellulose triacetate was invented and it combined the lower risks of diacetate with the je-ne-sais-quoi of nitrate base.

    Most 35mm and 120 films today are now coated on triacetate, except those that are coated on PET (which is even more stable).
    Using film since before it was hip.


    "One of the most singular characters of the hyposulphites, is the property their solutions possess of dissolving muriate of silver and retaining it in considerable quantity in permanent solution" — Sir John Frederick William Herschel, "On the Hyposulphurous Acid and its Compounds." The Edinburgh Philosophical Journal, Vol. 1 (8 Jan. 1819): 8-29. p. 11

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  5. #5
    AgX
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    The problem with finding a successor for cellulose nitrate was to find a foil that was much less flammable, had at least the same mechanical properties and (what is often neglected) was technically and economically (issue of solvents) feasible.

    And to add on Michel's post above: type APS films are coated on PEN.

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    Quote Originally Posted by Michel Hardy-Vallée View Post

    Professional films were often coated on cellulose nitrate, which is the nasty, inflamable and almost unextinguishable stuff.
    it was made with collodion / nitrocellulose ...
    think "movie house fire" kind of flammable ...
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    Hello evrybody,

    I read somewhere that films with PET base are prone to lightpiping. If I got it right, that's light entering from the edges of the film and scattering through, thus fogging the emulsion further in the cassete. A "cure" for that would be to load film in reduced light. Does anybody have personal experiece and/or knowledge on this?

    Thanks in advance.

  8. #8
    AgX
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    There are several things to consider concerning light piping:

    -) the light transmission of the clear form of the base material

    -) the reflectance of that material at its surfaces (subbing layer, air, backing layer, etc.)

    -) dying of the base material

    to name just a few.

    Of course with designing film intended for darkroom loading some of these points need not to be considered. However they could become important when converting such film to type 135.

    The general tone on type 135 films on PET base on the market at the moment is that the first 2 to 4 frames are at stake. I would add that when bulk loading by means of a daylight loader one should pay attention to the last frames as well.
    Think also about the chance of a cassette with a protruding `tongue´ lying around for some time.

    The best thing to do is to make a test with that very material under the worst circumstances you would expect while handling the cassette.

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    All films are subject to light piping!

    This is practially eliminated by the AH base on the film and inclusion of carbon in the film itself. The carbon serves two purposes, namely reduction of light piping and reduction in static electricity.

    PE

  10. #10
    Michel Hardy-Vallée's Avatar
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    Quote Originally Posted by jnanian View Post
    it was made with collodion / nitrocellulose ...
    think "movie house fire" kind of flammable ...

    Second language salad here: in French when something can burn, it's called "inflamable". In English it's "flammable" ...
    Using film since before it was hip.


    "One of the most singular characters of the hyposulphites, is the property their solutions possess of dissolving muriate of silver and retaining it in considerable quantity in permanent solution" — Sir John Frederick William Herschel, "On the Hyposulphurous Acid and its Compounds." The Edinburgh Philosophical Journal, Vol. 1 (8 Jan. 1819): 8-29. p. 11

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