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  1. #31

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    Several principles in physics and chemistry support this. it is also reflected in the Ilford procedure : 5 inversions, 10 inversions 20 inversions or words to that effect (its late here and I've already forgotten what I did read today!)

    The matter can be likened to driving force : i.e. the bigger the difference between the solution in the film layers and the clean water, the faster thiosulphate is driven out in the water and the faster the solution closes onto equilibrium.

    As the concentration goes down inside the film, less difference to the clean water, and the longer it takes. Eventually it will take *forever*!!

    These are general principles that works everywhere in solution and is used and recognized everywhere in chemistry, there is *nothing special* with thiosulphates!

    Your films are quite probably better rinsed than you thought, today over the net, all kinds of people weigh in, with absolutely no background, and sounds convincing....

    Back in the day I used to work in a club darkroom and observed a lot of people both developing film and paper, (we shared one bench, and had to synchronize things, so we didn't spill light at awkward moments). From those days I generally remember that most people used running water washing their films and left their tanks under the tap for more thasn an hour, instead of 30 minutes. Since it rains much here, noone gave that a thought....

    EP

  2. #32
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    Eric;

    Please rethink some of your "information".

    PE

  3. #33

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    There is theory and there is (are; for purists) empirical data.
    I have worked in a lab for decades.
    I know that empirical data ALWAYS tops theory.
    I trust Greg.

  4. #34

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    The main problem with the theoretical analysis of washing in running water, is that you can make two fundamentally different assumptions, which will lead to radically different conclusions.

    Assumption 1: The process is a gradual dilution, where the incoming water is perfectly mixed with all the water already in the tank. This is the worst case.

    Assumption 2: You have perfect laminar flow past the film, essentially a first in first out condition, and the incoming water simply pushes the old water ahead so the film is always exposed to fresh water.

    In reality, you will have a mix of these mechanisms, and you will have to experiment to find how efficient your method of washing is, depending on tank size, flow rate, and flow conditions.

    In contrast, a fill, agitate, and dump cycle is easier to analyze, since the agitation will ensure that the thiosulfate is more or less evenly distributed in the water at any time.

    Quote Originally Posted by brianmquinn View Post
    There is theory and there is (are; for purists) empirical data.
    I have worked in a lab for decades.
    I know that empirical data ALWAYS tops theory.
    I trust Greg.

  5. #35

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    Quote Originally Posted by Photo Engineer View Post
    Eric;

    Please rethink some of your "information".

    PE
    The ball is in your corner......

  6. #36

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    A major problem with the simple dilution theory of washing is the assumption that the fixer will almost immediately wash out of the emulsion and come to equilibrium with the fixer in the water. The dilution math would only work if you had 10 ml of LIQUID fixer in the tank. This is not the case. Greg’s test shows this to be true. No matter how may changes of water you do or how much water you use if the washing is too quick time wise all of the fixer can not diffuse out of the emulsion. Fixer also takes longer to diffuse out of hardened emulsions.

    Mees wrote that it takes about 5 minutes for the fixer in the film and in the wash water to reach equilibrium. ( I don’t know if this was a hardened emulsion). I also do not recall if he specified the rate that it takes place. So 90% may have washed out in the first minute. 99% after 2 minutes. And 99.9 after 3 minutes, etc.

    For this reason I use the Ilford wash method but wait 5 minutes after each set of inversions to dump and refill. After seeing Greg’s results I will have to rethink if the 5 minute wait is necessary.

    One thing I have noticed is the increased wait time DOES help remove more of the pink color from Tmax films.

  7. #37

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    The practical thing to do is do like me. Use 6 changes - tre in qiuck succession first, the 3 successions interspersed with TV watching and coffee drinking (a joke I develop films with cofee.....), usually I end up with one or two changes of water for good measure, yoiu know water in the tank before hanging the film, and add two drops of detergent in that last water.

    I do this because it suits me, is convenient and because I like a cup of coffee after all that inversing, shaking & rattling a tank!

  8. #38

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    I pretty much agree with that. The first rinse is quick. Then as washing is the last step I clean up the darkroom during the wait time. I also have a 4 year old who likes to hang out in the darkroom as I develop the film. He really likes to shake the tank and see what color the solutions change to when they are poured out of tank. Also I do a final rinse in Photo flow so I guess that really counts as 4 changes of water.

  9. #39

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    Quote Originally Posted by olehjalmar View Post
    In contrast, a fill, agitate, and dump cycle is easier to analyze, since the agitation will ensure that the thiosulfate is more or less evenly distributed in the water at any time.
    But even then, as others have noted you've got to account for the rate at which the fixer diffuses out from the emulsion into the solution. It seems like there are an awful lot of variables involved if you wanted to model that process theoretically, and I have more faith in the empirical results.

    On the bright side, most of my photos pretty much suck and it might be an artistic mercy if they decay over time anyway. Unfortunately it sounds from this thread like my descendants are likely to be stuck with them. ("Wow, Great-Grandpa couldn't focus his way out of a damp paper bag, could he?" :-)

    -NT
    Nathan Tenny
    San Diego, CA, USA

    The lady of the house has to be a pretty swell sort of person to put up with the annoyance of a photographer.
    -The Little Technical Library, _Developing, Printing, And Enlarging_

  10. #40
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    Quote Originally Posted by Erik Prestmo View Post
    The ball is in your corner......
    I think others are answering your post quite well.

    If you read the entire packet that comes with the Kodak test card, you will also have a fine explanation.

    PE



 

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