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  1. #1

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    Pyrocat-HD and Dichoric Fog

    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.
    Mike C

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  2. #2

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    Quote Originally Posted by photomc
    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.
    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
    Last edited by sanking; 05-03-2005 at 11:07 PM. Click to view previous post history.

  3. #3

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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.
    Mike C

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  4. #4

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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. #5

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    I found the answer elsewhere. Thanks anyway.

  6. #6

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    Quote Originally Posted by jdef
    I'm not convinced that the above is true. The Ilford rapid archival wash sequence uses three changes of water to wash all of the fixer out of the film, and developer is nowhere near as stubborn to remove. I use the first two steps of the Ilford method (fill with clean water, five inversions, change water, ten inversions, dump) and have not had any problems associated with developer carryover. Maybe a minimum of 5 changes without inversions accomplishes the same thing, but seems a waste.

    Jay

    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
    Last edited by sanking; 05-03-2005 at 10:53 PM. Click to view previous post history.

  7. #7

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    Quote Originally Posted by sanking
    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.
    Hear, Hear!

  8. #8
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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.
    Diane

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  9. #9

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    Quote Originally Posted by colrehogan
    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.

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

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  10. #10

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    Quote Originally Posted by colrehogan
    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.
    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

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