Pyrocat-HD and Dichoric Fog

Discussion in 'B&W: Film, Paper, Chemistry' started by photomc, May 3, 2005.

  1. photomc

    photomc Member

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    Developed some this weekend - had two sheets of film (both Efke PL100, 5x7). Exposure was the same for both films 1 sec @f/45 (see rail image here - this print is from the Rodinal negative).

    1st negative was processed in Pyrocat-HD 2+2+100, (or 10ml+10ml+500ml), negatvie was place in a Beseler 8x10 drum, pre-soak of 2 min in H20, the developer for 12 minutes, dump, water stop for 1 min., then fix for 5 min., rinse, and remove negative from the drum. The shadow areas along the rail, bottom center of the image, were just visible. Rest of the negative looked very good, except on the emulsion side, there was a slight amount of dichoric fog. Now, am using a Unicolor roller - going back and forth, is the fog coming from oxidation of the developer because of too much movement? The time does not seem out of line.

    The 2nd negative was processed in Rodinal 1+50 for 12 min also, same process with pre-soak, develop, H2O stop, and fix. That negative is the one placed in the gallery. The shadows have good detail and look pretty much like I had envisioned.

    When the scene was metered, place the shadows in Zone III and high lites were placed on zone VII..so the first impression I have is that I did not give the Pyrocat enough development time - which is OK, can understand that, but past experience has shown me the more time I give it the worse the dichroic fog will be - any suggestions. Really do like the look of the P-cat negatives, just wished I could figure out how to avoid the fog...

    As always thanks for your input.
     
  2. sanking

    sanking Member

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    Dichroic fog is a sheen which looks different when viewed by transmitted and reflected light. It is an iridescent sheen on the surface of the film that is sometimes formed by taking a film that still has developer in it straight into the fixer without being first passed through a stop bath. You could get the same result by the use of an exhausted stop bath, or as I suspect in your case, by the use of a water stop bath too short to remove all of the developer from the film. The problem could also be caused by exhausted fixer but I trust you take steps to avoid that.

    You have two choices. Increase the time of the water stop bath, making sure that you give the film several (minimum of five) changes of water, or use an acetic acid stop bath of about 1/2 normal strength. The acid stop bath will not reduce the image stain of negatives developed in Pyrocat-HD

    My experience is that films with fairly thick emulsion layer, and this describes most of the films from eastern Europe, are somewhat more prone to develop dichroic fog than modern thin emulsion films made by Ilford and Kodak. Regardless, the fix is very simple. Just switch to an acid stop bath.



    Sandy
     
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  3. photomc

    photomc Member

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    Sandy, perfect description of what I saw and did read somewhere a reference to the stop bath, but was afraid it would impact the stain. Thanks for the help, will give this a try with this week...really like the negatives I've gotten, cleared the fog with some Farmers , which worked quite well.
     
  4. David

    David Member

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    Sandy, I've often had problems with pinholes in the emulsion when using an acid stop bath (Efke PL25 and PL100). Because of the problem I just use water now. Is there an optimum dilution of the acid stop bath that gets around this problem and also precludes the diachronic fog?
     
  5. David

    David Member

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    I found the answer elsewhere. Thanks anyway.
     
  6. sanking

    sanking Member

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    Bear in mind that Ilford's archival washing procedures are based on processing in a spiral tank, where you fill the tank completely. Mike described processing in a 8X10 Unicolor drum rotated on a motor base. There is no way you can fill up a drum with water using rotary processing. In fact, the water will spill out of my 8X10 Unicolor drum when rotating if more than 500 ml of water is added. In my opinion three changes of 500 ml of water in one minute time (which is the time noted by Mike for the water stop) does not completely remove the developer.

    Actually, this is more than opinion. Several years ago, when I was still using a water stop bath and rotary processing some of my BPF 200 12X20 negatives developed dichroic fog with four changes of water (1000ml each change) over a two minute period. This is why I suggest a minimum of five changes for the rotary processing. In fact, five changes might still be insufficient to clear all of the developer.

    In any event, and based primarily on the above experience, I switched back to an acetic acid stop bath and have never seen any dichroic fog since then. It does not make any sense to me to spend two minutes, and five or more water changes, and still not be sure about the results, when fifteeen seconds of a dilute acetic acid stop bath does the job 100% of the time.


    Sandy
     
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  7. Kirk Keyes

    Kirk Keyes Member

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    Hear, Hear!
     
  8. colrehogan

    colrehogan Member

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    Sandy,
    How dilute would the acidic stop bath be? Is the acetic acid stop bath the same as the Kodak Indicator stop bath (I'm at work and don't remember what kind I have)? I have used this stop bath solution diluted according to the label and have had problems with pinholes with 8x10 FP4+ & Tri-X. I have switched back to a water stop bath and have had no problems.
     
  9. photomc

    photomc Member

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    Good question Diane...the reason I had moved to a water stop was due to a problem with pinholes.
     
  10. sanking

    sanking Member

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    I mix my own acetic acid stop bath from Glacial Acetic Acid. To do this I first make a Stock Stop Bath that is essentially a 25% solution of acetic acid by mixing 1 part of glacial acetic acid with 3 parts of water (for eample, 50 ml of glacial acetic acid with 150 ml of water). I then dilute 1.5 ounces of the stop bath with 64 ounces of water to make a working stop bath, which I believe is about 1/2 strength of Kodak's regular stock bath. You might be able to dilute the solution even more, but this works fine for me and I have not had a problem with pinholes.

    The dilute stop bath has good capacity but will need to be replaced sooner than a full strength sto bath as the pH will go neutral sooner.

    Sandy
     
  11. Kirk Keyes

    Kirk Keyes Member

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    I have some pH indicator strips and I used to just add enough indicator stop bath to the water to get the pH down to about pH 5 or 5.5. I think it's somewhere around 10 mls into 1 L. I haven't found the stain of PMK to be afftected by this level of pH.

    If one is doing non-stained films and wants a stop, I've been using the following (I haven't tested it with PMK yet as I did with the dilute stop I mantioned above.)

    After my big flap with Bill Troop last year on photo.net about stop baths and alkaline fixers, I've been using Bill's stop bath formula from the Film Developing Cookbook. It's a buffered acetic acid solution, made from acetic acid and sodium acetate. It buffers around pH 5 as well, but has a much higher acidity than unbuffered acetic stop baths - even if they have a lower pH. The increased acidity will speed up the stopping action of the stop bath, down to only a few seconds, according to the FDC. And since I use Rapid Fixers, which have a pH of about 5.5, I don't have to worry about all that emulsion swelling one should get by putting the film back into an alkaine fix. (Even though it really wouldn't be that much with a near neutral, alkaline fix.)

    Bill talks about this buffered stop being "expensive", but for film, I wouldn't worry about. Certainly much better than spending all that time doing multiple water washes and then not really stopping the development anyway.