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  1. #1

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    Bromide puzzler.

    I have a question for the chemistry gurus.

    In doing some testing with a new formula I had a rather puzzling finding in varying the amount of potassium bromide in the working solution. To this point I had assumed that one would find a linear relationship between the amount of bromide added and the degree of restraint obtained, i.e. that the least amount of bromide would produce the least restraint. However, in developing test films in developer to which I added, (a) no bromide, (b) 10 ml of a 0.05% of bromide, and (c) 20 ml of a 0.05% solution to a liter of working developer, the least amount of restraint was obtained with the developer to which I added 10ml of the bromide solution, not with the one to which none was added? In fact, a and c were virtually identical, but b showed much less restraining.

    I was so surprised by this result that I immediately ran the test again, with the same finding. So I looked in a number of references to see if there was any explanation for this in the literature. But I found nothing, and so today, after musing on the problem for a couple of days, I ran the test again. Same finding.

    I am really mystified by this. Anyone have any ideas what is going on? I am reasonably certain that my results are valid. I used the same emulsion batch, exposed with a light integrator, developed with the same mix of the developer (the only difference being the amount of bromide added), and I developed all of the tests together at the same time in a water bath.

    Sandy

  2. #2

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    This is not surprising, the error was in assuming a linear response to the restraining action. We run into this problem in the water treatment field when trying to flocculate. For example, ferric sulfate is a great floculant if used in the exact amount. If you use too little you get no floculant, if you use too much the same. You have to tailor the exact amount to the chemistry of the water. Of course, being that the floculant addition is most of the time done by operators, their idea is that if a little bit works, putting a lot works a lot better...... this is why they usually end up with red lakes...at least here in Mexico...

    MOst likely what is happening in your developer is that some of the oxidation by products are acting as a sequestering agent for bromine. If you have no bromine then the developer is not "capturing" any of the bromine, if you have a lot of bromine as in the case of the 20 ml, then you are having left over to cause restraint, and by serendipity you found out that the 10 ml solution has just enough bromine to be "captured" and leave you sodium ions which might be causing you fog.

    Anyhow, dont be surprised it happens.

  3. #3

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    You might see a linear relationship if the action of bromide were simple. However, it is rather complex. For example, there are two types of fog, emulsion fog and developer fog. If you are interested I would suggest doing some reading on the subject. Not much has been published in quite a while. Modern Photographic Processing by Grant Haist is good but assumes a lot from the reader.

  4. #4

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    Quote Originally Posted by Gerald Koch
    You might see a linear relationship if the action of bromide were simple. However, it is rather complex. For example, there are two types of fog, emulsion fog and developer fog. If you are interested I would suggest doing some reading on the subject. Not much has been published in quite a while. Modern Photographic Processing by Grant Haist is good but assumes a lot from the reader.
    I have the two volume set by Haist and looked through it last evening but could not find anything that I thought relevant to my situation. If you see something that might pertain to this please point me to the page.

    Sandy

  5. #5
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    Sandy, it depends on what your film or paper is as well as developer. Iodide in films is a powerful restrainer as well. Bromide reacts differently with Bromide papers than Cl/Br papers and Cl papers.

    Dektol contains about 2 g/l in the stock and diluted 1:3 would be 0.5 g/l which is a lot higher than you used, whereas D76 for film contains no bromide.

    PE

  6. #6

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    Quote Originally Posted by Jorge
    This is not surprising, the error was in assuming a linear response to the restraining action. We run into this problem in the water treatment field when trying to flocculate. For example, ferric sulfate is a great floculant if used in the exact amount. If you use too little you get no floculant, if you use too much the same. You have to tailor the exact amount to the chemistry of the water. Of course, being that the floculant addition is most of the time done by operators, their idea is that if a little bit works, putting a lot works a lot better...... this is why they usually end up with red lakes...at least here in Mexico...

    MOst likely what is happening in your developer is that some of the oxidation by products are acting as a sequestering agent for bromine. If you have no bromine then the developer is not "capturing" any of the bromine, if you have a lot of bromine as in the case of the 20 ml, then you are having left over to cause restraint, and by serendipity you found out that the 10 ml solution has just enough bromine to be "captured" and leave you sodium ions which might be causing you fog.

    Anyhow, dont be surprised it happens.
    Thanks for the explanation.

    BTW, based on this finding I may soon recommend a reduction in the amount of potassium bromide in the Pyrocat-HD stock solution. What this observation has suggested is that we can get a slight bump in EFS and a modest bump in CI (for a given time of development) by reducing the amount in a liter of Stock from 2.0 grams to 1.0 grams. The only down side is a very slight increase (log 0.01) in B+F.

    Sandy

  7. #7

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    Quote Originally Posted by sanking
    BTW, based on this finding I may soon recommend a reduction in the amount of potassium bromide in the Pyrocat-HD stock solution. What this observation has suggested is that we can get a slight bump in EFS and a modest bump in CI (for a given time of development) by reducing the amount in a liter of Stock from 2.0 grams to 1.0 grams. The only down side is a very slight increase (log 0.01) in B+F.
    Sandy
    Would the addition of a small amount of benzotriazole help lower the B+F to its previous level. The action of the organic restrainers is different from that of bromide and they are prefered with Phenidone containing developers

  8. #8

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    Quote Originally Posted by Gerald Koch
    Would the addition of a small amount of benzotriazole help lower the B+F to its previous level. The action of the organic restrainers is different from that of bromide and they are prefered with Phenidone containing developers
    Interesting suggestion, and I will try it. I am also going to try some potassium iodide in combination with the bromide.

    I am of course concered about making any modifications that might change the acutance characteristics of this developer. Any ideas on how a small addition of BTZ or P. Iodide might impact acutance? I was thinking that the iodide might increase it slightly?

    Sandy

  9. #9
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    Quote Originally Posted by sanking
    I have a question for the chemistry gurus.

    In doing some testing with a new formula I had a rather puzzling finding in varying the amount of potassium bromide in the working solution. To this point I had assumed that one would find a linear relationship between the amount of bromide added and the degree of restraint obtained, i.e. that the least amount of bromide would produce the least restraint. However, in developing test films in developer to which I added, (a) no bromide, (b) 10 ml of a 0.05% of bromide, and (c) 20 ml of a 0.05% solution to a liter of working developer, the least amount of restraint was obtained with the developer to which I added 10ml of the bromide solution, not with the one to which none was added? In fact, a and c were virtually identical, but b showed much less restraining.

    I was so surprised by this result that I immediately ran the test again, with the same finding. So I looked in a number of references to see if there was any explanation for this in the literature. But I found nothing, and so today, after musing on the problem for a couple of days, I ran the test again. Same finding.

    I am really mystified by this. Anyone have any ideas what is going on? I am reasonably certain that my results are valid. I used the same emulsion batch, exposed with a light integrator, developed with the same mix of the developer (the only difference being the amount of bromide added), and I developed all of the tests together at the same time in a water bath.

    Sandy
    A number of years ago I saw, in a translation from Russian of a photography reference book, a graph showing an actual increase in activity of a phenidone developer as bromide was added up to a certain point. I don't remember the title of the book. It was in the NASA Langley Research Laboratory library. I don't recall having to use my secret clearance to get it. In fact, I'm sure I didn't as I kept the book in my desk for quite a while. I just don't know how to tell you what to look for so that you may see for yourselves.
    Gadget Gainer

  10. #10

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    Sandy, are you talking about 5mg/L and 10mg/L or KBr in developer solution? That is strange. How many square inches or dm^2 of film is developed in how many ml of developer? What's the film and how was it exposed?

    This is because, average exposure given to a typical modern 100 speed film (80 sq. in.) would release about 50mg KBr equivalent of bromide during development. Say you develop this in 500ml developer, and it is already on the order of 0.1g KBr/L at the end of development.

    I don't doubt what you got but I suggest to run the test again with different exposure patterns, different developer volume per film area, with different film, etc. to verify if the result holds across a wide range of practical conditions before you draw any conclusions out of it.

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