Potassium Bromide for fogged paper **UPDATE**

Discussion in 'B&W: Film, Paper, Chemistry' started by bmac, Apr 19, 2004.

  1. bmac

    bmac Member

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    I was given some old enlarging paper today. I am assuming that it will most likely be fogged (at least a bit). It is ilford ilfobrom and AGFA Brovira (grades 4 &3). I have read that Potassium Bromide can be added to developer as a fog restrainer. I currently have a bottled solution of 10% KBr. How much should I add to 1 liter of developer?

    Thanks,
    Brian "Mad Scientest" McGuiness
     
  2. Donald Miller

    Donald Miller Member

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    Brian,

    KBR is normally used in developer formulation to diminish or eliminate the fog creating characteristics of certain developing agents. That is a different matter then trying to reduce the fog on old paper...at least in my experience.

    For old paper that may be suffering from fog due to age I would add Benzatriazole to the paper developer.
     
  3. john_s

    john_s Subscriber

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    Like old fashioned wines, old paper can last a lot better than the modern ones.

    If it's really old, you could be in luck. Believe it or not, Brovira purchased in February 1973 here in Melbourne Australia and stored at temperate room temp is free of fog. I remember the date because of events at the time (honeymoon, faulty camera, visit to local camera shop on its last day and buying them out of Brovira at clearance price. The boxes still have the price labels on them.)
     
  4. skahde

    skahde Member

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    I bought some old record rapid on ebay recently and it was foggy. I salvaged it by reducing my developing time from 2min to 1min and adjusting the exposure accordingly. It was argued that you should always develope to completion. Richard Henry in "Controls in black & white photography" conclusively demonstrated that you can adjust for different developing times between about 1min (shorter = uneven) and fogging-time (8.5 min in his case with fresh Kodabromide) by exposure and end up with indistinguishable results.

    Imagine your paper as being preflashed as an approximation of what happened to it. Shortening developement so that the flash is below instead of above threshold and increasing exposure accordingly to reach Dmax parts the wanted from the unwanted density.

    I owe this to Tim Rudmans "Master Printing Course" where he mentions that Benzotrizole can be used to save foggy paper if developing times were reduced to 1 min. This made me think about what is going on here and what the chemicals like KBr and Benzotriazole are doing. As far as I understand the literature, KBr acts more like a general restariner (shifting the balance between free Bromide and AgBr towards the Bromide, slowing its release). So what you usually do is add some KBr, keep developing times constant and get a print that is to light on the first shot. What is next? You will most certainly adjust exposure to compensate and get to the Ds. I think it is already obvious that you had been reducing development chemically but could as well have shortened it, getting the same result. With Benzotriazoel things seem to be a bit different but I am not sure yet about the practical consquences and I don't find it worth testing until I see any need for it.

    best

    Stefan
     
  5. Jorge Oliveira

    Jorge Oliveira Member

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    I agree with the posting by Donald - benzotriazole is better at cuttailing fog.

    Jorge O
     
  6. Tom Hoskinson

    Tom Hoskinson Member

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    I agree with Donald and Jorge.

    I have found Benzotriazole to be better than Potassium Bromide at preventing or reducing fog. It is also used as a paper developer additiive to produce blue/balsck tones.

    Potassium Bromide is generally used in paper developers to restrain development and to produce warm or neutral tones. Too much bromide can raise fog levels.

    I would not add either chemical without testing their effects on the paper/developer combination.
     
  7. bmac

    bmac Member

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    I did a quick test of the ilford ilfobrom and AGFA Brovira (grades 4 &3) this evening.
    The top sheet in each box was fogged just at the edge. I took a random sample from the middle of the stack, and no fog whatsoever! (i think)

    My method of testing was to put an unexposed sheet of paper in dektol for 3 minutes and see what developed. I then fixed the paper and turned the house lights back on to inspect. This was all done under a safelight.

    From reading the unblinking eye site, it looks like this paper is good for solarization. Anyone here use it?