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  1. #281
    Steve Smith's Avatar
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    Based on all the information in this thread, I am going to carry on using just plain water. I can see that there may be some advantages to using a stop but I don't think they will be of any benefit to me - perhaps they will be to others.

    This is for film only. For prints I will continue to use a stop bath.


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  2. #282
    clayne's Avatar
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    I can think of one small benefit beyond the obvious: you waste less water.

    It's actually logistically easier to use stop-bath.
    Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.

    http://www.flickr.com/kediwah

  3. #283
    Curt's Avatar
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    Quote Originally Posted by Steve Smith View Post
    Based on all the information in this thread, I am going to carry on using just plain water. I can see that there may be some advantages to using a stop but I don't think they will be of any benefit to me - perhaps they will be to others.

    This is for film only. For prints I will continue to use a stop bath.


    Steve.

    Me too Steve, it's what I do and it works just fine.
    Everytime I find a film or paper that I like, they discontinue it. - Paul Strand - Aperture monograph on Strand

  4. #284
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    My observations are only anecdotal in nature, rather than scientific observations, but I processed my first films in the mid sixties. A few had stop baths in the processing, but being a penurious schoolboy, the stop bath often had to give way to plain water. I've noticed nothing to indicate any difference in stability as the result of not using a stop bath ; I had far more problems with insufficient final washing than anything else. I worry far more about temperature control than the post-dev rinse, which is plain water and has been for decades for me. It's been an interesting thread, though it's not persuaded me to change my processing routine.
    Alex

  5. #285
    Thomas Bertilsson's Avatar
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    Kind of like American politics...

    But then again, I think if Republicans and Democrats actually agreed on something - it's time to worry.

    Quote Originally Posted by Q.G. View Post
    Thought about it, and yes: i'm sure it's impossible to reconcile.
    It is possible to accept that there is a conflict between both views though. But reconcile, i don't think so.

    I mean, you too haven't managed to, but have chosen a side instead.


    And that (choose a side) is the only thing we can do, i guess.
    "Often moments come looking for us". - Robert Frank

    "Make good art!" - Neil Gaiman

    "...the heart and mind are the true lens of the camera". - Yousuf Karsh

  6. #286
    Photo Engineer's Avatar
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    Quote Originally Posted by Ray Rogers View Post
    Was that a typo?
    (post #126)

    Anyway guys,
    this topic has been beaten to a pulp!

    Nothing much to learn here
    (other than the unpublished Kodak science from PE' s noggin).

    Ian keeps saying water is OK,
    but seems IMHO to interpret Kodak etc. as saying they are equivelant
    PE on the otherhand clearly feels they are saying they are unequal
    but acceptable options.

    Is this such a hard concept to reconcile?

    Water is OK. It is not IDEAL. It is NOT ideal because there is less of a safety margin....

    Stops are preferable. They are not absolutely necessary.
    In fact, they are ideal... but usually not absolutely necessary.
    Ray;

    Thanks for the catch. That is a typo in my post #126.

    Thanks also for an excellent summary of these posts.

    PE

  7. #287
    Photo Engineer's Avatar
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    All I can say on my own behalf is that, I do not disagree with what Kodak or any other mfgr says. They say either can be used for film, but there may be consequences thereby making them unequal. They say that a stop should be used for paper.

    PE

  8. #288
    Photo Engineer's Avatar
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    Quote Originally Posted by alanrockwood View Post
    I think the best approach now for our sub-discussion is to take it in a series of small steps to best avoid misunderstandings or confusion.

    Let us set up a coordinate system to help clarify the discussion. Let the solution be on the left and the emulsion on the right.

    One implication of the model you have posed, together with the coordinate system defined above is the following. There is a net displacement of charge to the right. In other words, the emulsion is a slab of material that acquires a net positive charge because positively charged hydrogen ions have been transported into the emulsion. This leaves a net negative charge in the solution, most of which will be in a relatively thin layer near the solution-emulsion interface.

    A related effect occurs with the hydroxide ion, though to a lesser degree. They diffuse from the emulsion toward the solution. This is because the the concentration of hydroxide ions is higher in the emulsion than in the solution. This process adds to the net positive charge in the emulsion, i.e. removing negative ions (hydroxide ions) from the emulsion increases the net positive charge in the emulsion.

    We will consider the other ions to be relatively fixed in space because they diffuse much slower than hydrogen ions (and hydroxide ions.) This is of course an approximation.

    With respect to the reaction between hydrogen ions and hydroxide ions, this has no effect on the local net charge balance. This is the result of charge conservation. For example, let us consider a single hydrogen ion (do you mind if I just call them protons?) in close proximity to a single hydroxide ion. Considering only these two ions and not any other ions that may be in the vicinity, the net charge of the proton-hydroxide pair is zero. If these two ions then react to form a water molecule there is no change in the net local charge. Therefore, with respect to the location of the charge distributions there is no need to consider the acid-base neutralization reaction. (There could be an indirect effect because the neutralization reaction may change the concentration gradients, which in turn can affect the diffusion rates, but this is a fine point that need not concern us at this point.)

    Let us see if we can agree that this description is a consequence of the model you have proposed.
    I can agree to a point.

    There are other ions present such as Sodium, Bromide, Carbonate and Acetate to name a few, and listed in rough ascending order of size and therefore diffusion rate.

    In any acid base neutralization of one proton and one hydroxide, there is an instantaneous charge imbalance at that site as a neutral water molecule is formed. This, in our example, would leave a negatively charged acetate ion somewhere on the left and a positively charged Sodium ion on the right, and they have to move somehow together. So, if it occurs on a grander scale over several square inches, but on a time scale of microseconds, then there is not much difference. I viewed it, when I first learned of these tests, as if I were seeing a high speed collapse of a row of dominoes.

    Now, after looking up the data, I find that my 15" was conservative by a long shot. According to Henn and Crabtree, depending on pH and acid concentration, the reaction can be over in about 1 second throughout the entire emulsion. But, at the other end of the scale, 15" is not a bad guess when using dilute acid or when at a higher pH.

    The original tests were done by imbibing the indicator dye and then adding the acid and measuring the change in the dye. Later we coated the dye and mordanted it in place.

    PE

  9. #289
    Ian Grant's Avatar
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    Thank you Ron, and to clarify those consequences are to the potential life & throughput of the Fixer used. There's no possible potential later consequences for the film.


    Kodak have no wash or stop-bath stage in their Versamat/Duraflo film processing, matching Fuji's equivalent, which ties in with Mason saying the stage is "superfluous". However Ilford do recommend a stop bath with their RT system if the processor has the facilities to use one, (I think their own machines used one), for the same reasons Mason cites, that a stop bath improves the potential stability & throughput of the Fixer.

    Ian

  10. #290
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    Ian;

    Please note that there are established limits for retained developing agents in film and paper. I posted the reference to work done with Monobaths above, but it has been done in a similar fashion for all types of processes. Since HQ and Metol are opposites in terms of one being a weak organic acid and the other a weak organic base, they do differ in their reactions to different pH values and have different wash rates.

    I'm sorry that I still have not found any published works on this particular subject, but I assure you that it is part and parcel of the "later consequences" for film and paper both. In fact, Haist refers to a minimum acceptable level of HQ for image stability.

    One of the reasons a final wash is so long is to remove the HQ from a coating. It is reportedly removed at a slower rate (in general) than Silver Hypo complexes. Of course, this single article is difficult to extrapolate into all real world conditions, but nevertheless, knowing it happens should alert us.

    PE



 

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