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  1. #1

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    The trouble with Pyro - part 1

    I thought I would post some data for discussion - if anyone is interested.

    This is part of a low-flare/no-flare test of 35mm Delta 100 in PMK. One of the purposes is to try for some cold hard yes/no answers to questions like:

    -Is imagewise stain pH sensitive post development?
    -Does imagewise stain intensify if a post-fixer alkaline bath is used?
    -Does an extended wash intensify imagewise stain?

    Rather than test one variable at a time, I wanted to first try an all-out "ideal" treatment ("control") versus a rule-breaking treatement ("pressure"). If there was any significant difference observed between the bookend scenarios, I'd continue investigating the variables.

    The development regime was the same in both treatments. All solutions were mixed with distilled water (with the exception of running wash water). Standard PMK dilution. All solutions and running wash water were at 22C. Post-development as follows:

    Control
    -1 minute running water rinse
    -5 minutes in TF-5 fixer
    -2 minutes in spent developer
    -30 minute wash

    Pressure
    -30 seconds in Kodak Indicator Stop Bath at standard dilution (16ml/l)
    -5 minutes in Ilford Rapid Fixer
    -10 minute wash

    Densities were read with a black and white densitometer to determine "visual" readings. Since I don't own a color densitometer, the "blue channel" readings were then made using a Wratten #47 filter. The results are attached.

    As expected, the silver densities appear to be virtually identical with the possible exception of a very small amount of additional density in the low values in the "control" scenario, which is either simple experimental/measurement variability, or a very small amount of compensating development occuring in the water "stop" bath.

    As for the stain measurements, it is fair to say I am confused. To be honest, what I expected was either no significant difference at all, or a difference in general stain only.

    Key stain observations
    1. Base fog (visual and blue) were the same
    2. "Control" scenario shows more film speed and shadow density from stain
    3. Beyond the zone IV exposure, the increase in stain in the "control" scenario relative to the "pressure" scenario is essentially constant, rather than proportional

    Observations (1) and (3) above would appear to contradict eachother to some extent. The conditions in the "control" scenario seem to add some imagewise stain (ie proportional, contrast-increasing stain) up to a point - the zone IV exposure, after which there is no further increase in contrast.

    How can this be?
    Attached Thumbnails Attached Thumbnails Ilford Delta 100_PMK_1a.JPG  
    Last edited by Michael R 1974; 08-11-2012 at 09:53 PM. Click to view previous post history.

  2. #2

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    Quote Originally Posted by Michael R 1974 View Post
    ...
    As expected, the silver densities appear to be virtually identical with the possible exception of a very small amount of additional density in the low values in the "control" scenario, which is either simple experimental/measurement variability, or a very small amount of compensating development occurring in the water "stop" bath...
    Michael,

    You've partially answered your own question. In your "control" scenario you are getting more development happening from reactivated carried-over developer. A short water stop will decrease developer activity somewhat, but not rinse all the developing agents out of the emulsion. Transferring this negative to an alkaline fixer will re-activate those developing agents and give more development until the fixing removes enough of the undeveloped halides to stop development. This development is of a compensating nature, as you guessed, and affects the mid and lower values proportionally more than the higher densities (where the developer will exhaust rather rapidly without making much of a density difference).

    I imagine this happens all the time for people who use alkaline fixers for their film (even if they use an acid stop in between), but is of little importance; as long as the system is tested and calibrated, results will be consistent. I would say you have "discovered" a compensating effect of using an alkaline fixer.

    I'd recommend that you use the same fixer for both tests to eliminate this variable if you wish to test other the other things you mention.

    FWIW, I've stopped using alkaline fixers for film after experiencing streaking from carried-over developer being re-activated in the fix and turning on the light "too soon," i.e., halfway through the fixing time. I'd rather not have to deal with that.

    Best,

    Doremus

    www.DoremusScudder.com

  3. #3

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    Hi Doremus, thank you for responding. A couple of things...

    1. TF-5 is an almost neutral pH (slightly acidic) rapid fix as opposed to TF-4 which is alkaline. I used TF-5 because I had it on hand but I guess ideally in the "control" scenario I would have used an alkaline fix (note I'm referring strictly to PMK in this case because it is much more finicky about pH than Wimberley's formulas).

    2. Re compensating development, the thing is the densitometry here showed the effect on silver density to be very small, possibly even within the margin of measurement error (refer to the two visual channel curves).

    So what I'm really trying to explain are the differences in the blue channel readings, and this is where I'm stumped. Even if there is some small amount of compensating development in the control scenario, why is the apparent difference in imagewise stain so pronounced compared to the difference in silver densities? Why is the apparent increase in imagewise stain in the control scenario not proportional to silver density? If we compare the two blue channel curves, it would appear the additional stain in the control scenario is not only imagewise stain, but is non-proportional. It is only materially affecting the densities below middle grey. It's as though the additional stain gained in the control scenario is "compensating imagewise stain". ?

  4. #4
    Rick A's Avatar
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    In the Book of Pyro, Gordon Hutchings espouses the use of diluted acid stop bath (50% normal) prior to fixing. This book deals primarily with PMK pyro. He also prefers TF-4 for fixing. This is then followed with a 30 second immersion(continuous agitation) in the spent developer to induce the formation of stain.
    Rick A
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    BTW: the big kid in my avatar is my hero, my son, who proudly serves us in the Navy. "SALUTE"

  5. #5

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    Rick, The Book of Pyro was part of the reason for this test, since even Hutchings himself now says you only need the alkaline after-bath if your wash water is acidic. My problem with these formulas in general is that most of the recommendations don't come with supporting data, and the proverbial jury always seems to be out on the impacts of various processing procedures on stain. The after-bath is only one example of several variables that may or may not impact general stain or imagewise stain. And unfortunately in the case of PMK, I have been unable to find any definitive testing or conclusions out there. Generally if it isn't Kodak or Ilford, we have to rely largely on anecdotal evidence. For most developers, this is not a huge issue because the variables are limited and testing is relatively straight forward. But when it comes to Pyro, stain can in some cases be a tricky thing. Concerning any Pyro formula I need to understand how to get the following:

    1. Maximum imagewise stain
    2. Solid consistency/repeatability

    Unfortunately the answers are simply not out there. And PMK is the trickiest due to its alkali system and the way in which its stain forms.
    Last edited by Michael R 1974; 08-12-2012 at 08:38 PM. Click to view previous post history.

  6. #6

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    Speaking of which, does anyone know how I might be able to contact G. Hutchings directly? I'd like to ask for his commentary on this data.

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    You might be able to contact him via Freestyle. As I recall he is on their "professional's council" or whatever they actually call it.

  8. #8

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    Thanks, bdial. I will try that.

  9. #9
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    I found this on the Freestyle website - http://www.freestylephoto.biz/board/...wer.php?id=248 . It's an answer to your question about the alkali bath. He no longer recommends the alkali bath post-fix if your wash water is neutral-to-alkaline, only if your wash water is acidic.

  10. #10

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    Yes - but I'm trying to figure out whether there exists such a thing as "compensating stain induction". If yes, it would appear it has a very significant effect on film speed.

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