Bromide puzzler.

Discussion in 'B&W: Film, Paper, Chemistry' started by sanking, Sep 9, 2005.

  1. sanking

    sanking Member

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    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. Jorge

    Jorge Inactive

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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...... :smile: this is why they usually end up with red lakes...at least here in Mexico... :smile:

    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. Gerald Koch

    Gerald Koch Member

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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. sanking

    sanking Member

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    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. Photo Engineer

    Photo Engineer Subscriber

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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. sanking

    sanking Member

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    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. Gerald Koch

    Gerald Koch Member

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    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. sanking

    sanking Member

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    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. gainer

    gainer Subscriber

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    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.
     
  10. Ryuji

    Ryuji Member

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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.
     
  11. Ryuji

    Ryuji Member

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    This is irrelevant. The specie that is involved is bromide, not bromine, and bromide does not react with developer oxidation product. The restraining mechanism of bromide is well understood in terms of electrochemistry but this has nothing to do with the interaction suggested above.

    It is true that the action of bromide on chloride emulsion is different (a different mechanism kicks in). But my guess is that Sandy used a camera negative emulsion and this is probably not the case.
     
  12. Ryuji

    Ryuji Member

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    This is not really the case. It really depends on the aim of the developer design. Benzotriazole, or preferrably more strongly adsorbing antifoggants may be necessary in color developers, but they are not necessary in phenidone developers. (of course, they can be used for certain ends, but not generally necessary.)

    The reason some develoeprs (like color developers) require strongly adsorbing organic antifoggants is because the developing agents have stronger adsorption to AgX crystals and this is a competition for adsorption. Phenidone has stronger adsorption than Metol in regular developer conditions but nothing like color developing agents.
     
  13. Photo Engineer

    Photo Engineer Subscriber

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    Interestingly, neither the C41 nor RA color developers use an organic antifoggant. The C41 developer relies on a Br/I mixture and the RA developer relies on a Cl/Br mixture for antifogging.

    Organic antifoggants used in color developers adsorb so heavily and selectively, they tend to act on a single layer or component in the color material and can therefore be bad rather than good.

    The only negative product color developer to rely heavily on an organic antifoggant and selective action on a layer was the CP-100 series of developers used for high temperature drum processes for Ektacolor Professional Paper, T1920 and similar products in the 60s.

    Organic antifoggants are used in color negative films as DIR fragments to control interimage and image structure. E6 films are another matter entirely.

    PE
     
  14. sanking

    sanking Member

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    Ryuji,

    OK, I will be more specific. I did not give a lot of detail in the first message because the results surprised me so much I was just trying to find out if there was anything in the literature that could explain them. If not, I may need to re-think the testing methodology to see if there is an error.

    First, the developer. The working developer was mixed from regular Pyrocat Stock A and B solutions, but with no bromide. I mixed one liter for the test, and each liter would contain the following.

    sodium metabisulfite -----0.1g
    pyrocatechin --------------0.5g
    phenidone -----------------0.02g
    potassium carbonate -----10.0g

    The test film was Ilford FP4+. I used 100ml of solution per sheet of 4X5" film, so each sheet was developed in 1/10 of the above amounts. That is, in 100ml of developer there would be the following.

    sodium metabisulfite ------ 0.01g
    pyrocatechin ----------------0.05g
    phenidone -------------------0.002g
    potassium carbonate --------1.0g

    Development was in BTZS type tubes with constant agitation. Three sheets of film were developed, in separate tubes but from the common solution, and they were developed together in a water bath. The only difference was in the amount of bromide added to the developer. Sample A contained no KBr, Sample B contained 0.001g of KBr, and Sample C contained 0.002g of KBr.

    The sample tests were made by contact printing a Stouffer TP45 step wedge, using a standard light set-up that I dedicate to film testing in which exposure is controlled with a light integrator.

    When I read the densities here is what I found

    Sample A (no bromide)
    Step 21 ----- .14
    Step 11 ----- .59
    Step 1 ------1.42

    Sample B (0.001g of KBr in 100ml developer)
    Step 21 ---- .13
    Step 11 ---- .63
    Step 1 ------1.54

    Sample C (0.002g of KBr in 100ml of developer)
    Step 21 ----.12
    Step 11 ----.59
    Step 1 -----1.45

    I did this test three times and got similar results each time. The B+F values are higher than what I expect with FP4+ sheet film, but this particular film is several years old and has developed about log 0.6 of film base fog. I could easily do the same tests with other film but before I waste my time doing that I wanted to post the results to see if anyone could find an obvious flaw in the methodology of the testing itself.

    Sandy
     
    Last edited by a moderator: Sep 10, 2005
  15. Ryuji

    Ryuji Member

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    Sandy, I have no very confident explanation for this, but my suspicion goes to the use of fogged film. Fogged grains (due to emulsion aging at improper condition, etc.) are rather different from emulsion uniformly exposed to weak light exposure. Fogs often develop in smaller grains while light exposure would render larger/sensitive grains developable. Small grains have greater surface area to volume and they are great adsorption sites, and if they are developable, they may consume a significant amount of developing agents. But bromide might have worked preferrentially against fog development at certain concentration.

    Another concern is the use of relatively small amount of developer for testing like this. I know BTZS tubes users usually use small amount of developers and continuous agitation, but when you are testing developers, the developer performance should really be tested in large baths first, and then determine how low the volume can be cut down without noticing the difference. Otherwise, when you get some idiosyncratic results particualr to some film or exposure, you may be trying to make a dangerous generalization without knowing. You could still use BTZS tube if you could cut the films in 1/4 and use smaller step tablet, for example.
     
  16. gainer

    gainer Subscriber

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    So, you don't trust the Russians? Or you think I made it up. Oh, well.
     
  17. john_s

    john_s Subscriber

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    Sandy, what is interesting to me is that in your three sets of density figures above, not only is there a difference in the fog level, but a significant difference at higher densities. I use Pyrocat-HD without bromide (roll film, for VC paper), my reasoning being that reducing the restraining effect would perhaps give me a smidgen more speed with an insignificant increase in fog. But maybe I'm actually "back at square one" and it's effectively the same as standard pyrocat-HD. Strange.
     
  18. sanking

    sanking Member

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    Well, I ran the same test this afternoon with TMAX-400 and got slightly different results. The results were more linear as I had expected from the FP4+ film. Here are the densitometer readings for Visual, Blue and UV light. I did the test twice with very similar results. Here is data from one of the sets.

    Visual-----(A) No KBr ---(B) 0.005g Kbr/liter---(C) 0.02 g KBr/liter
    Step 21-------1.39------------1.36---------------------1.32
    Step 11------- .67--------------.66----------------------.61
    Step ----------.12---------------.12----------------------.12

    Blue-----(A) No KBr ---(B) 0.005g Kbr/liter---(C) 0.02 g KBr/liter
    Step 21-------1.63------------1.61---------------------1.56
    Step 11------- .79--------------.77----------------------.72
    Step ----------.16---------------.15---------------------.15

    UV------(A) No KBr ---(B) 0.005g Kbr/liter---(C) 0.02 g KBr/liter
    Step 21-------2.27------------2.23---------------------2.08
    Step 11-------1.20------------1.18---------------------1.02
    Step ----------.37--------------.28---------------------..27

    People can conclude what they will from the data, but what I conclude is that if you are printing with TMAX-400 negatives on silver papers, both graded and VC, the formula is optimum with no KBr at all. However, if you are printing with both silver and UV sensitive processes the best compromise appears to be adding about 0.005g - 0.01g KBr/liter of working. This can be achieved by reducing the amount of bromide in the Stock A solution from the present 2.0 grams per liter to 0.5g - 1.0g per liter.

    Irrespective of the reason for the non-linear anomaly in the FP4+ tests, all of the data suggests that the formula is slighly optimized with the reduction of KBr in a liter of Stock A from 2.0 grams to 0.5g - 1.0g.

    Sandy
     
    Last edited by a moderator: Sep 10, 2005
  19. Kirk Keyes

    Kirk Keyes Member

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    Sandy - I would like to suggest that when measuring differences of 0.01 density, you are probably not likely to get any significance to any one measurement by simply making one measurement.

    Your densitometer is probably repeatable to +/- 0.01 OD at that density level. And then there will be differences in the manufacture of the films you are testing, even though I suspect you are trying to minimize that by using sheets from the same production lot number or even the same box.

    One way to try and get more precise readings when you have measurements that differ by this little is try to read each Step several times. If your densitometer has a sensor size that has a diameter of 2 or 3 mm, make several measurements across the length of the step. Space the readings apart by a distance that is a millimeter or so larger than the diameter of your sensor diameter. Then average the readings. While you are at it, figure out the standard deviation.

    If you really want to minimize things, read a spot on one film, then the next film, and then the third. Then move to the second spot on the first film and repeat the process until you get across the Step on all 3 films. This will hopefully eliminate any variation in reading based on time from your densitometer. Drawing a grid on to the Step can help with this.
     
  20. Kirk Keyes

    Kirk Keyes Member

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    Were they using polywater to dissolve their chemicals? See http://www.cs.cmu.edu/~dst/ATG/polywater.html

    Anyway - I've always enjoyed this exchange from Dr. Strangelove:

    General "Buck" Turgidson: A-A-Am I to understand that the *Russian* ambassador is to be admitted entrance to th-the War Room?

    President Merkin Muffley: That is correct, he is here on my orders.

    General "Buck" Turgidson: I... I don't know exactly how to put this, sir, but are you aware of what a serious breach of security that would be? I mean, he'll see everything, he'll... he'll see the Big Board!
     
  21. sanking

    sanking Member

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    Kirk,

    Variation in density depending on where the measurement is taken on the step wedge are not common in my testing, though they are not rare. I would estimate that when measuring the twenty one steps of a wedge some eighteen to twenty of the individual steps will measure exactly the same in the middle and on the far edges. The other one three may show a variation of log 0.01 depending on exactly where the reading is taken. Variations of more than 0.01 are very, very uncommon. With develoment in tubes I usually eliminate the method of development as a cause for variations over log 0.02, so if I see something on this magnitude in a test I know to look outside of the develoment process itself for the reason.


    Sandy
     
    Last edited by a moderator: Sep 11, 2005