Why does unexposed film get fogged with age?

Discussion in 'B&W: Film, Paper, Chemistry' started by BetterSense, Jun 11, 2009.

  1. BetterSense

    BetterSense Member

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    I have heard and experienced that old film becomes fogged with age. I have heard that it is caused by cosmic rays. What kind of cosmic rays? Does anyone actually know? Could they be stopped by lead?

    I have also heard that freezing unexposed film will prevent fogging. However, using film for photography at freezing temperatures doesn't seem to effect the film's speed or sensitivity, so why should putting it in the freezer slow down fogging?
     
  2. DannL

    DannL Member

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    Oxidation of the silver in the emulsion. Molecular activity slows as temperature is decreased.

    True or false?
     
  3. Photo Engineer

    Photo Engineer Subscriber

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    Heat fogs film. Radiation will fog film. Heat fogs faster than radiation. Fast films fog faster from both sources than slow film. Freezing slows down heat death of film. Heat death is a continuation of the sulfur + gold finish placed on film to speed it up photographically. (in simple terms)

    Film changes at any temperature at a finite rate, but more slowly at low temperature. Temperature does not materially affect speed, but rather the rate of change of speed.

    I hope this answers your questions.

    PE
     
  4. Photo Engineer

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    Oxidation = false. :sad:
    Siver in emulsion = false. :sad:

    PE
     
  5. DannL

    DannL Member

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    Oh well, I got that info from a publication describing a kodak film. It sounded good at the time. I should have known better. :D
     
  6. wiltw

    wiltw Subscriber

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    Kodak had an article about accumulation of cosmic rays. Cosmic rays penetrate freezers, so while freezing might slow color shift in films, it will not do much to slow accumulation of cosmic radiation.

    Cosmic rays are resultant from our own sun and other stars. Cosmic rays originate outside our solar system. They consist of ionizing particles such as electrons, and atomic nuclei and non-ionizing particles such as gamma rays (photons), and neutrinos. Nuclei from every element and nearly every isotope are found.
    The most common of these are hydrogen (protons), and helium nuclei. Those nuclei formed in stars, such as carbon through iron, are the next most abundant.

    As for lead, I just found this description in a NASA publication about the methods used to shield a detector from cosmic rays,
    "Passive shielding is used to stop low-energy cosmic rays before they hit the CZT detectors. EXIST uses layered sheets of lead (Pb), tin (Sn) and copper (Cu). This layered approach is called "Graded-Z" shielding, which refers to the order and atomic number (Z) of those metals (Z equals 82 for lead, 50 for tin, and 29 for copper). Materials with larger Z have greater stopping power, and lead is used for the outermost layer. When a low-energy cosmic ray hits the lead it will be absorbed and ionize a lead atom which then emits an X-ray at the "characteristic energy" of lead, 88 keV, in a random direction. Lead does not absorb its own X-rays very well, so to prevent any of those X-rays from getting through the shielding, a layer of tin comes next. After absorbing the 88-keV X-ray, the tin may then emit a 29-keV X-ray. A layer of copper comes last. The few copper X-rays that reach the CZT detector are too low in energy (9 keV) to cause a problem. "

    So simple lead alone is insufficient, as it is necessary to shield from the secondary radiation byproducts that result from the cosmic rays striking the lead, too!
     
  7. jim appleyard

    jim appleyard Member

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    Kryptonite is the real killer tho'!
     
  8. MikeSeb

    MikeSeb Member

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    Wow. What interesting arcana! A trove.

    I love this place!
     
  9. Q.G.

    Q.G. Inactive

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    Except, of course, the big part of it produced by "our own sun". :wink:
     
  10. Mahler_one

    Mahler_one Member

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    Cosmic rays, and stray radiation added to the incredible effect of Grandma's Gefilte Fish...sorry, I just couldn't resist...
     
  11. Photo Engineer

    Photo Engineer Subscriber

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    Dont worry. I was kinda tongue in cheek. :D

    Sorry.

    There is little or no silver in film. It is 99.999+% Silver halide with some sulfides present and other silver salts. Any silver metal is there as a latent image if the film is exposed and that is quite resistant to oxidation. The latent image is in very low concentration and can fade with time as well.

    I shield all of my film from Kryptonite radiation! :D

    The Van Allen belt created by the magnetic field of the earth does a good job off keeping the sun's radiation away, but a poorer job with the higher energy of the cosmic background radiation. Much of the sun's radiation is in the form of neutrinos that go right through us and our film with no harm being done whatsoever.

    The bottom line is that there is no easy way to preserve film from heat and radiation effects.

    PE
     
  12. ic-racer

    ic-racer Member

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    Stockpile slow film.

    It is less sensitive to all the nasties. By using the required low exposure index and blasting the film with photons, the ratio of photon exposure to cosmic ray exposure favors the latent image.
     
  13. Sirius Glass

    Sirius Glass Subscriber

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    Even better: Stockpile developed film. It does not fog! :tongue:

    Steve
     
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  15. Kirk Keyes

    Kirk Keyes Member

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    Outer Space is not the only sources of radiation. Since no one has mentioned it, the Earth itself is a source as well. Or your house. Or your granite counter tops.

    Depending on where you live, the bedrock or the soil under your house can give of radiation or radon gas, which is radioactive as well. If your house is made of rock or bricks, it will likely be more radioactive than a house made of wood.

    And the bit about granite countertops - I was talking with the state radiation officer a few months ago, and he was saying that some agencies are investigating measure granite counter tops to make sure the amout of radiation they release it safe. He found it interesting as granite, being a natural product, did not typically fall under his sphere of concern. He said granite is typically not a big issue, but he said the veins of red that are found in some granites are the areas of interest and much more radioactive than typical granite.
     
  16. 2F/2F

    2F/2F Member

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    Isn't there any way film can be stored to reduce its exposure to fogging radiation? I have often wondered if a block of ice and metal layers surrounding the film (water/lead layers are used as a radiation shield in nuclear plants) or even storage in a hefty metal box would help Delta 3200 and HP5 keep longer. Of course, I am talking about building a dedicated storage unit here...probably converted from a commercial top-loading freezer. I am dreading the day when fast films disappear...gotta plan ahead!
     
    Last edited by a moderator: Jun 11, 2009
  17. nocrop

    nocrop Member

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    There are far more relevant things to worry about, at least until the next "significant" galactic gamma ray burst hits us, which happens on average about every billion years.
     
  18. 2F/2F

    2F/2F Member

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    I just remembered "squiggle", as we called it in the plant. It is "linear attenuation coefficient". Every potential shield material has one for each type of EM radiation. (Solid particles are halted by physical barriers, but upon collision of a certain force, can create radioactive isotopes within the shield material that can then stabilize via release of EM radiation.) All you need to know is *what exact kinds* of rays cause the fogging, and you can design an efficient shield pretty easily. I wish I still had my thermoluminescent detector and a way to read it, though average levels should be easy to find.
     
    Last edited by a moderator: Jun 12, 2009
  19. Vaughn

    Vaughn Subscriber

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    I have some friends who bought 1000 rolls of infra red film from Kodak's last run (Kodak would not let them buy more). They are off to Europe this summer to use up the film before it fogs.

    Sometimes that is the best storage solution...exposed and developed film does not fog with age.

    Vaughn
     
  20. Ray Rogers

    Ray Rogers Member

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    Any indication on the thickness for each of the layers required ?

    ???
    ---
    I think Kodak did some storage in underground salt mines ....
     
  21. Photo Engineer

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    Kodak stored no raw film or paper stock in a salt mine. Among other things, the salt dust would be murder on raw film.

    They did store duplicate business records and formulas in a mine somewhere. Perhaps it was a salt mine, but IDK. It may have been a cave. In any event, this storage of backup data is a routine storage service for large companies.

    PE
     
  22. Ray Rogers

    Ray Rogers Member

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    More Tongue in Cheek?

    Tell us about Batavia.
     
  23. Mark Layne

    Mark Layne Member

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    Rubbish -it's the Lepracauns:D
     
  24. Europan

    Europan Member

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    Ahm, heavy water, deuterium oxide, not natural water
     
  25. Photo Engineer

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    Ray;

    There are salt mines in this area, but are sometimes subject to flooding. There are caves out west used for storage. Kodak, to my knowledge, has used both at one time or another, but not for product storage.

    PE
     
  26. cmacd123

    cmacd123 Member

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    heavy water is radioactive anyway.