Does preflash dissipate over time?

Discussion in 'B&W: Film, Paper, Chemistry' started by cdowell, Jan 29, 2011.

  1. cdowell

    cdowell Member

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    Potentially a dumb question, but I feel like I've read that somewhere. I'm wondering if I can pre-flash lots of paper for use as paper negatives and then use it weeks or months later. Or does the energy dissipate over time, if not pushed over the threshold into actual chemical change/gray tones? Thanks.
     
  2. Bob Carnie

    Bob Carnie Subscriber

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    Wow thats a good question, I think the big brains need to jump on this one,

    I would think that flash/fog would be permanent lots of paper like Fuji Metallic have a heavier Dmin that give it character and I think this is exactly how it would be done.

    I will be interested to see the answers on this one.
     
  3. pentaxuser

    pentaxuser Subscriber

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    From what I have read here and elsewhere it does dissipate over a relatively short time like a few days only and wouldn't last weeks or months. There are probably several threads on this. Do a search. Someone is almost bound to have mentioned how long pre-flashing remains.

    pentaxuser
     
  4. Hikari

    Hikari Member

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    The short answer is that it can. The latent image is not always stable and can fade. However, you need to run test to find out the stability of the latent image. For film it is a larger problem as people keep their film in the camera a long time and so much research has gone into improving the stability of the latent image. Paper is more likely to be developed after exposure so it is not a very big concern for paper emulsion designers.
     
  5. Bob Carnie

    Bob Carnie Subscriber

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    Thinking of this a bit more.. Metallic colour paper is grey where it should be white, therefore I assume they have pre flashed, from time of manufacture to time of usage it could be months if not years. therefore I believe the OP will be ok pre flashing, for film I cannot say.
    Ron M would be the go to guy to answer this one IMO
     
  6. jtzordon

    jtzordon Member

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    How about post-flashing? I do that with paper negatives in my pinhole camera to good effect. Sometimes during development the shadows aren't registering, so I give it another pop.
     
  7. Stephen Benskin

    Stephen Benskin Member

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    Preflashing and reciprocity failure both fall under the heading of latent image keeping and both deal with low energy exposure and time. Immediately after exposure silver atoms that will develop may give off electrons and convert back to silver halide. This happens proportionally more in the shadows where there are lower exposure levels. Most of the loss happens in the first few seconds after exposure and tends to plateau off after a few hours. This is the reason there is a hold time between exposure and processing in the ISO standard for testing for film speed.

    It's probably best to test if you are planning on doing preflashing. Then be consistent with you hold time if you are using a short preflash to exposure ratio.
     
    Last edited by a moderator: Jan 29, 2011
  8. Gerald C Koch

    Gerald C Koch Member

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    In books that mention preflashing and describe the technique it is always done just before the actual print exposure.
     
  9. sepiareverb

    sepiareverb Subscriber

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    I've been wondering about paper negatives from a pinhole camera- can they be processed a week after exposure without trouble?