Split Film

Discussion in 'B&W: Film, Paper, Chemistry' started by Tom Kershaw, May 13, 2005.

  1. Tom Kershaw

    Tom Kershaw Subscriber

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    A few days ago a was handling a strip of 120 Delta 100 film by the edge. However, when I used some compressed air to blow the dust off, much to my surprise, the film actually split about a third of the way across the negative. I've never had this happen before, and wonder if it was just improper handling of whether something happened to the film during processing to make it more vulnerable?

    [​IMG]

    Tom
     
  2. Donald Qualls

    Donald Qualls Member

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    Does the split go through the base, or only the emulsion? It's possible the film got brittle due to the chill of the canned "air" product and simply broke (though I'd normally expect that to require the film being well below 0F/-18C). If it's emulsion only that's split, I'd think it might be related to extreme overdrying of the gelatin.
     
  3. Tom Kershaw

    Tom Kershaw Subscriber

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    The base split. I suppose the film could have just got very cold from the compressed air. However, I've used the same brand of canned air on many occasions without problems.
     
  4. Donald Qualls

    Donald Qualls Member

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    Normal use of canned air shouldn't result in acetate or mylar film base getting cold enough to become very brittle -- these films can be used in cameras, with accompanying flex and tension, to well below 0F/-18C.

    If it's acetate film, it's remotely possible the acetate is decomposing (if so, you'll start to see problems with all film stored with this), though that's a relative rarity, and I"m not at all sure Ilford films are on acetate anyway; they might well be on polyester.

    If there was a nick in the film edge, a surprisingly small amount of tension could cause the nick to extend into a tear, due to stress concentration at the point of the tear, and the tear can proceed with amazing speed. Not likely, though, when handling the film by the edges. This process could be greatly accelerated or exacerbated by rapid movement of the film in response to high velocity gas flow over the edge (the same vortex shedding that can make a thin film whistle in a suitable flow); this seems the most likely reason for this to occur just when you were blowing the film off with a canned air product.

    So, my best guess, there was a small nick at the film edge (possibly induced when cutting the negative strip, or by the camera, or even from the factory), and the tear proceeded with great rapidity from there due to high frequency vibration induced by the gas flow from your canned "air". Microscopic examination of the torn edge might reveal (depending on the base material) the stretching that would go with tearing under local tension.
     
  5. Tom Kershaw

    Tom Kershaw Subscriber

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    Thanks for the informative response. I'll have to take a closer look at the film. According to the Delta 100 PDF from Ilford's website, 35mm and 120 films are on acetate base, while Delta 100 sheet film is coated on polyester.