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  1. #1
    Reinhold's Avatar
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    pH change in PC-TEA ?

    Does anyone know how much the pH changes after developing 80 square inches (120 roll) of HP5 per liter of developer? The anti-halation dye makes it impossible to get a reading with pH papers, and I don't have a meter.

    The reason for the question is that I have a project involving about 40 pieces of 8x20 film, and I'd like to concoct a replenisher that would let me develop about 10 sheets (successively) in my 3 liter capacity tray instead of having to dump it every sheet or two. (Developing multiple 8x20 sheets is out of the question... I cannot avoid scratching the film.)

    I develop by inspection, so a small amount of activity loss is insignificant, but I suspect that the pH would get out of hand if I try to boost the developer with regular PC-TEA after each sheet or two. If the pH change is insignificant after developing a sheet, I might be able to use an Ascorbic acid/phenidone/propylene glycol booster to keep the developer capacity up without elevating the pH. But that's only speculation at this time.

    Any ideas?

  2. #2

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    I'm sure Patrick Gainer will be along to provide the best answer, but in the mean time I'll post my speculation. Then I'll see how right I am when Patrick comes by.

    Ascorbic acid developers become more acidic after development, so you could probably replenish with PC-TEA. 500 ml of PC-TEA will develop 160 square inches of film (a 220 roll), so perhaps 5-10 ml of added PC-TEA per sheet would be about right.

    But I don't think this scheme will work for 40 sheets, because you'll get bromide build-up in the developer that will change things no matter how you replenish. Better to dump every 5-10 sheets or so, especially since the developer will be susceptible to aerial oxidation.

  3. #3
    gainer's Avatar
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    I'm sure you can get a processing tube for 16X20 film or prints. I used to have one until I got a housekeeper. The cup on the end held less than 500 ml, more like 250, and I'm sure it will do one of your sheets. It's not much of a solution if you are intent on development with inspection, but it will solve your problem of developer freshness. It is easy to mix 250 ml of PC-TEA at a time. I have used such a tube in the past without a mechanical rotator just by rolling it an see-sawing it in my hands. You can also float it in a water bath and keep it spinning by hand.

    If you have never used one, don't worry. It's easy. With the tube standing on end, pour the appropriate amount of developer in. It stays in the cup until you turn the tube on its side. Just make sure the emulsion is toward the center of the tube, not against its wall.

    I'm not much for development by inspection. It's too easy to be fooled. Some developers start slowly and accelerate, others start with alacrity and slow down. I would rather trust time and temperature, but that's a matter of opinion.
    Gadget Gainer

  4. #4
    Reinhold's Avatar
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    Peter:

    Thanks for the tip about the pH shift with ascorbic acid developers. I kind of guessed that the pH would drift lower. I guess I'll have to monitor the activity and be prepared to adjust things as I go. The potential for bromide build-up is why I plan to limit the films to no more than 10, assuming I can get the replenishment rate settled.

    Your statement about the capacity being at least 160 square inches per 500 ml of PC-TEA is interesting. I usually develop 3 rolls of 220 film in a dip & dunk acrylic cylinder using 3 liters of PC-TEA, one-shot. Works beautifully, but I've never been sure how much capacity has been used by those 480 square inches of film. I'll still use it one-shot for 220 film, but it's interesting to contemplate how awesome that tiny splash of PC-TEA is as a developer.

    Patrick:

    The idea of putting an 8 inch wide film into a tube designed for 16 inches makes me nervous (not enough "hoop" stiffness to hold it in place?). To make me even more nervous... every time I try rotary tube processing, I get streaking, regardless of how I dance, wiggle, and slosh the tube to eliminate eddy currents. I gave up on tubes years ago.

    I've been developing large format film by inspection for 20+ years, my "keepers to loosers ratio" is much better than if I use the time/temperature system. (Mis-judge a meter reading, forget a filter factor, close down the aperture inaccurately 'cause you can't see it when it's 2' overhead, and it's easy to get an exposure that's not quite right). By inspection, I can compensate for those kinds of "hiccups".

  5. #5
    gainer's Avatar
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    I was wrong about my tube. It is for 11X14 stuff. 2 of those taped end to end would hold an 8X20 with plenty of arch, I think. A couple of layers of black electrician's tape overlayed by some duct tape (we who have lived in Newport News, VA call it shipyard tape} should do the job.

    The capacity for film of the working solution is quite good. It is the ascorbate that is used up first. I did some experiments to find the optimum initial ratio of ascorbic acid (as sodium ascorbate) to phenidone, holding phenidone and pH constant and varying ascorbate. The activity as measured by contrast index after a given development time increased with ascorbate concentration asymptotically to a ratio somewhere above 80:1 but rather slowly after 40:1. While the 80:1 ratio does not give much greater initial activity, it will have greater capacity both for film and for aerial oxidation. The ratio I use in PC-TEA is about 40:1.

    You see that some conceptions of how to increase the activity of a PA or PQ developer are in error. If the initial ratio is less than 40:1, add more ascorbate. This means that if you are using ascorbic or isoascorbic acid, you need to add enough alkali to keep pH constant. If the ratio is at or above 40:1, add more of both phenidone and ascorbate in the ratio of 40:1. In other words, add a little more PC-TEA.
    Gadget Gainer

  6. #6

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    In my experiments, varying the phenidone/ascorbic acid ratio affected not only the activity of the developer, but the shape of the curve. More phenidone yielded more shadow development, while more AA gave denser highlights.

  7. #7
    gainer's Avatar
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    I kept phenidone constant and varied only ascorbate, as I said. The shadows didn't change much after 10:1. The whole curve didn't change much in any way after about 40:1. If I can get my brains together, I will try to post the graph of the results.
    Gadget Gainer

  8. #8
    gainer's Avatar
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    Synergism between sodium ascorbate and phenidone

    Attached is the promised graph, I hope.
    Gadget Gainer

  9. #9
    gainer's Avatar
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    I don't see it. If someone will give me a basic lesson in how to make it seen, I will be very happy.
    Gadget Gainer

  10. #10
    gainer's Avatar
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    Next try.
    Gadget Gainer

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