pH change in PC-TEA ?

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

  1. Reinhold

    Reinhold Subscriber

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    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. psvensson

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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. gainer

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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.
     
  4. Reinhold

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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. gainer

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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.
     
  6. psvensson

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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. gainer

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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.
     
  8. gainer

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    Synergism between sodium ascorbate and phenidone

    Attached is the promised graph, I hope.
     
  9. gainer

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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.
     
  10. gainer

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    Next try.
     
  11. gainer

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    I think its in here somewhere. Anyway, I posted it in the Technical Gallery and I saw it there.
     
  12. psvensson

    psvensson Member

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    I couldn't find it in the technical gallery.
     
  13. gainer

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    Synergism between sodium ascorbate and phenidone

    The graph should be attached to this message.
     

    Attached Files:

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  15. gainer

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    Ah Ha! It's there!
    8 g/l of ascorbate corresponds to 80:1 ascorbic acid to phenidone, etc.
     
  16. psvensson

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    Cool. I should do a similar chart, keeping AA constant and adding phenidone. Would have to wait till January, at least.
     
  17. gainer

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    I forgot to indicate on the chart that the film is HP5+.
     
  18. psvensson

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    I'm intrigued to see that the curves for the lower ratios appear attractively S-shaped, while the highest dilution is ramrod straight. I'm pretty curious what they would look like if they were processed to the same zone VIII density.
     
  19. Reinhold

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    Thanks, everyone for your suggestions...

    Patrick:

    I'm using your 40:1 ascorbic acid formula, but I could whip up a batch of 80:1 for this project, so I'll have the reserve capacity. (Although..., simply adding 5 or 10 ml of PC-TEA will keep the alkalinity up, which answers my first question. Hmmmm....)

    Peter:

    It looks like your first suggestion was right on target...
    Incidentally, I use a variant proposed by Sandy King, in which I add 0.2 g of KBR to stop the streaking problem that used to plague me in the past.

    Jay:

    Now that I'm confident that my developer won't die after the first sheet, I'll probably make up a few pre-measured 5 or 10 ml batches of PC-TEA (diluted 2:1 or 3:1, so it'll blend in quickly), which I can toss into the tray after every other sheet, up to about 5 or 6 sheets maximum. My washer holds 10 sheets, so a 2-batch session before a beer break is about right.

    As we both know, capacity and activity are not the same thing. The 3 liters may have capacity for 6 sheets, and if I could develop them all at once, the time would be a constant (say; 7 minutes). But if I develop them successively, the time must be increased successively to match the reduced activity (say, +10% for each succession). So the timing might be something like this: 7 min, - 7.7 min, - 8.5 min. - 9.3 min. - 10.2 min - 11.3 min., etc....

    You're right, changing the developer every hour or so is not a big hassle. I make up a few 3 liter batches ahead of time (96 oz Chlorox bottles are perfect), and can make a dump/change in a few minutes.

    If you ever come down Portland way, give me a call.. we could have fun making the neighbors suspicious with big tripods, and funny looking dark cloths....
     
  20. gainer

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    Don't be too enthralled. The step wedge was not calibrated. There are the usual sources of experimental error. If you look closely you will see that all the curves have some curvature. It is more apparent in the low contrast curves. The straight lines are those of best fit according to my spreadsheet program.
     
  21. gainer

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  22. dancqu

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    If you keep adding more and more phenidone and no more A. acid, the
    shadow density will increase, that according to your previous remark.

    Perfection XR-1 is film developer with very high levels of phenidone and
    fractions of it's amount of hydroquinone and metol. Substituting A. acid
    for the hydroquinone may boost shadow density even more.

    XR-1 is noteworthy for the two to three stop speed increase
    it provides. Dan
     
  23. dancqu

    dancqu Member

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    Two whys:
    Why is density on the left and why the negative values for exposure. Dan
     
  24. gainer

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    If you believe that, try it and report it to us. I did not get that from my previous post. I have not found any developer that would give me increased shadow density without also giving me increased contrast. True there are certain developing agents that are more efficient than others, but sticking to a given pair won't buy you much in that regard.

    The density scale is always on the left unless you put it on the bottom. The negative values are because the scale is "Log of relative illumination." I have not the wherewithal to measure absolute illumination. All test film strips were on the same roll of 35 mm film, exposed in the same way at the same time. In any case, the relative exposures are always smaller to the left, so if the largest log is 0, the smaller ones will be negative.

    Any strip from that roll of film would give me the same intercept at the left end of the scale from any developer I have. The contrast would vary with time of development or concentration of developing agents. I chose to hold phenidone constant for these tests. If I change phenidone concentration and went through the same variation of ascorbate, I would get a different family of curves, but all would still emanate from the same point.
     
  25. gainer

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    I used that developer years ago. In those days it gave a speed increase, but no more than everyone was getting. The films were rated much lower in speed than the same film would be now because the ASA ratings were not used by the ISO. I also tried Acutol, in spite of the ridiculously impossible curve shape they touted to show "compensation". It was OK and still is, but PC-TEA is capable of duplicating the curve shape. I have done the comparison.
     
  26. psvensson

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    Repeating one of my posts at photo.net:

    I made a version of PC-TEA with twice as much phenidone and called it 2PC-TEA. At 1:70, 76F, 9 minutes, it gave a contrast index of 1.2 on Delta 400, and a true speed of perhaps 640. This is a bit better than I would get with PC-TEA. Grain is not great, but not very objectionable either. Some of the sharpness of Delta 400 is lost. I also tried 1:100 at 10.5 mins at got a ci of 1.1 with a touch more shadow speed.

    I tried 2PC-TEA 1:100 on Tri-X as well, but this time with two tbsps of sulfite per liter. At 76F, 8mins, it gave ci of 0.9 at a staggering speed, probably 800 ASA. Full developed to a ci of 1.2, the speed is going to be whopping. The grain is quite big for Tri-X, but sharpness is not too bad.