Emulsion speed in Gainer formulas

Discussion in 'B&W: Film, Paper, Chemistry' started by psvensson, Aug 30, 2004.

  1. psvensson

    psvensson Member

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    Some of you may have seen my complaints about graininess in sulfite-free phenidone-ascorbic Gainer formulas on photo.net. I've experimented a bit further, and have managed to get fine grain without sulfite by keeping pH low. Using borax + boric acid works, for instance, as does TEA (though this is somewhat surprising, since I believe borax should have a lower pH all by itself than TEA).

    The problem is that with low pH, shadow speed is also quite low, perhaps a stop or 2/3 below D-76 on Tri-X and Delta 400. Adding back some sulfite helps increase emulsion speed, but grain increases too, at least until I add so much sulfite that the solvent effect starts to kick in (at perhaps 50g/l) - and then I'm back where I started.

    One thing I've noticed is that doubling the amount of phenidone, without increasing ascorbic acid, raises the shadows. This fits in with the description of phenidone as a developer that works quickly but doesn't acheive much contrast. However, the Delta 400 negs get a somewhat odd, mushy look. Haven't tried printing them yet. If I increase phenidone by less than double, the speed bonus decreases proportionately.

    Anyone have any suggestions on dealing with the speed issue, apart from downrating the film?
     
  2. gainer

    gainer Subscriber

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    The pH of TEA varies more with concentration than does that of borax. A part of the TEA is used to form some kind of compound with the ascorbic acid, as is the sodium part of the borax, but I don't have the wherewithal to find out all the ins and outs of the differences between sodium ascorbate and triethanolaminoascorbate or whatever it is.

    Which of my formulas are you using that gives reduced film speed? Let me know and I will try to track it down. Also, what contrast index are you shooting for?
     
  3. psvensson

    psvensson Member

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    Hi Patrick!
    Thanks for the info about TEA - that makes sense. I'm trying to get approximate 1.25 density on zone VIII (this is for a diffusion enlarger). Here are some of the things I've tried:

    PC-TEA: 1l water, 4 ml phenidone in 91% rubbing alcohol as per your recipe on unblinkingeye.com, 1/2 tsp ascorbic acid and 20 ml TEA. 76F at 9 min on Delta 400 gives good contrast and grain but weak shadows.

    I know, I could dissolve the phenidone in the TEA instead of using alcohol, but I already have the alcohol solution and it allows me to vary phenidone, AA and TEA independently of each other. As you can see, I'm already using more phenidone than the 2.5 ml you recommend.

    PC-BB: 1l water, 2.5 ml phenidone in alcohol, 1/2 tsp ascorbic acid, 2 tsp boric acid (finely powdered, from drugstore), 2 tbsp borax. 70 F 11 min on Tri-X: good contrast and grain, but speed is maybe 200ASA.
     
  4. psvensson

    psvensson Member

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    I should clarify that it's zone VIII density less zone I density that should be 1.25. I guess that's a contrast index of around 0.6. I just measured the PC-TEA strip and got a density range of 1.20, so that's pretty close.
     
  5. psvensson

    psvensson Member

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    Never mind - I think I found the answer. The phenidone-alcohol solution was losing strength. I mixed up some real PC-TEA and found it to be much more active than the equivalent amount of alcohol+TEA. I thought the phenidone would keep more than a few months in alcohol, but I guess it will depend on its purity and how you store it.
    The PC-TEA gives adequate shadow speed, but now that I saw the effect increasing phenidone had on the shadows, I'm going to see if I can get even more speed out of the film by adding more phenidone.
     
  6. sanking

    sanking Member

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    Just for the record I want to report that I have done BTZS testing of the PC-TEA formula with FP4+ (9 g of ascorbic acid and 0.25 g of phenidone in TEA to 100 ml of solution) and compared the results in terms of film speed with a number of other developers. My tests do not show any loss of film speed with PC-TEA at 1:50 in comparision to the D76 1:1 standard.

    I add the phenidone directly to the stock solution when mixing it.

    Sandy
     
    Last edited by a moderator: Sep 8, 2004