Benzotriazole vs. Potassium Bromide

Discussion in 'B&W: Film, Paper, Chemistry' started by analogfotog, Apr 23, 2008.

  1. analogfotog

    analogfotog Member

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    I am trying to compound a developer which has slightly more contrast and slightly less density than the modified AGFA-Ansco 17M I have mixed. I mixed it with 5x the normal amount of sodium metaborate, as recommended in the old Ansco literature I have, to increase both the contrast and density. I would like a bit more contrast, and a bit less density. The info I have from Troop's "The Darkroom Cookbook," page 105, indicates to effect that change I should increase both the amount of hydroquinone and the restrainer, potassium bromide (KBr).

    I am wondering if, instead of the KBr, I could try benzotriazole. I have mixed a 0.2% solution, for use with paper, and if anyone could advise me on how much to start with, I'll give it a whirl. My fallback position is to increase the hydroquinone to 4.0g/l, from 3.0g/l, and to double the KBr to 1.0g/l, from 0.5g/l. Any input would be appreciated!
     
  2. Ian Grant

    Ian Grant Subscriber

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    The bromide will help the contrast. Benzotraizole is usually only added to Phenidone type developers to give colder tones. Try cutting the carbonate & raising the sulphite as well.

    Ian
     
  3. George Collier

    George Collier Member

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    I thought Benzotriazol was added to print developers to keep highlights clean. At least that's what I remember from Fred Picker.
     
  4. Tom Hoskinson

    Tom Hoskinson Member

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    With Phenidone based developers, I add Benzotriazole when I want Blue/Black tones.


    I keep percentage solutions of both KBr and Benzotriazole handy when I'm printing. Dilution, sulfite and alkali are also "knobs" that can be used.
     
  5. Nicholas Lindan

    Nicholas Lindan Advertiser Advertiser

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    Benz and bromide work differently.

    Benz gets rid of paper fog - where silver has already started to form in the emulsion before it has started to develop. Benz forms a waterproof polymer when it contacts any metal and this keeps the developer from acting on the grain. Once the the developer starts acting the benz has less effect. The major use of benz is rustproofing. It only works on paper that is fogging because of storage, it won't help with paper that has been fogged by light. It will change the image tone to cold as there will be fewer very small grains of silver in the resulting print as the benz has kept them from the developer action.

    I find benz won't completely recover age-fogged paper, but a few seconds in Farmer's Reducer will get the paper back to white before anything happens to the highlights.

    Bromide restrains the developer so that a lightly exposed grain takes longer to develop. It will keep the highlights clear but won't do as much for already age fogged paper. It will help with light-fogged paper. It will change the image tone to warm as, with the lessened developer activity, the developed silver grains will be finer.

    Finer silver grains are why very dilute developers will form a warm-tone image.
     
  6. Photo Engineer

    Photo Engineer Subscriber

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    Nicholas;

    Here is a quote from a patent reference:
    =======
    "On the other hand, although triazoles such as benzotriazole and imidazoles are used for preventing eluation of non-ferrous metals such as copper and copper alloys, and cobalt ions of super-hard alloys, these compounds are also unsatisfactory in respect to rustproofing abilities. "
    =======
    Benzotriazole does not work in all cases as a corrosion inhibitor and rustproofing agent, and with silver halide the reaction is totally different and also sometimes failes with respect to being an antifoggant.

    Benzotriazole, phenyl mercapto tetrazole and nitro-benzimidazole nitrate are all classed as antifoggants in photo engineering usage. They adsorb to the crystal surface and form mild to strong salt like materials or complexes with the silver halide to reduce development rate and fog formation. These complexes are much less soluable than the original silver halide itself. While doing so, they also 'tone' the image changing the color of the silver metal by changing the form taken by developing silver metal.

    Bromide is one of the constituents of a grain in many cases and retards development simply by changing solubility of silver halide or by a counter ion effect. Development produces halide. If you add enough of the halide to the developer to start with, development slows down. Fog slows down, speed slows down and contrast lowers. Of course, this is often the same result as the antifoggants I list, but by a slightly different method. It also requires different amounts of each of these to get to approximately the same point.

    PE
     
  7. nworth

    nworth Subscriber

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    Benzotriazole works with all developers as an antifog agent. As mentioned above, it helps with development fog and fog caused by aging. It tends to cool print tones very slightly. It is said to increase contrast a bit, but I have not seen this. Potassium bromide is a less effective antifog agent, but it still has that effect. It tends to warm tones a bit, depending a lot on the paper and the developer it is used in.
     
  8. jim appleyard

    jim appleyard Member

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    Wouldn't it be easier to decrease your exposure to give you less density and increase your dev time to increase contrast? Just a guess.
     
  9. BradS

    BradS Subscriber

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    PE,
    Thanks for this very lucid and complete explanation. It is very helpful and interesting.

    Brad.
     
  10. Anscojohn

    Anscojohn Subscriber

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  11. Photo Engineer

    Photo Engineer Subscriber

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    One way to increase contrast without reformulating the entire developer is to increase pH. You can do this by adding a 10% solution of Sodium Hydroxide to the developer and using pH paper to test for the desired contrast.

    The down side is the need to test (but you would anyhow if you reformulated) and you would sacrifice developer stability. As pH goes up, stability goes down.

    PE
     
  12. Nicholas Lindan

    Nicholas Lindan Advertiser Advertiser

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    That's probably a new low for a 'quoted expert source'. If you are quoting a patent for a corrosion inhibitor that is promoting itself as superior to the prior art - benzotriazole - what do think it is going to say? "Unsatisfactory to whom?" is the question to answer.

    Google "Benzotriazole rustproofing". Microencapsulated benz is used in naval paints, the benz is released when the paint is scratched and bonds to the exposed metal. It isn't usually associated with steel but with preventing corrosion and tarnishing on copper and silver.

    This is getting silly ... correspondence closed.
     
  13. Photo Engineer

    Photo Engineer Subscriber

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    Nicholas;

    I did exactly that google search and the first thing that came up was that quote. I thought it rather amusing. And of course, from that POV in your post above, you are completely correct.

    Yes, it can passivate metals from forming metal salts. Isn't that somewhat what I described? I was being tongue in cheek though referring to the patent! The action in photography was not quite as you described though if you read my post.

    You said: "Benz forms a waterproof polymer when it contacts any metal and this keeps the developer from acting on the grain. Once the the developer starts acting the benz has less effect. " , and this is really quite incorrect. The actual reaction or action if you will is in my first post here. It appears that you couldn't get past the part that offended you. I'm really sorry about that.

    AAMOF, all 3 compounds I mention are also used as corrosion inhibitors on metals. The interesting difference here that you missed is that in the case of corrosion inhibition, the compounds prevent oxidation or corrosion of the metal to form a salt, and in photography, the 3 compounds act essentially on the salt to prevent formation of the metal (fog). Think about that.

    In photo engineering circles, benzotriazole is referred to BTW, as BTAZ.

    :D

    PE
     
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  15. Ray Rogers

    Ray Rogers Member

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    Now THAT is absolutely amazing!
    Could you be more specific as to how I can use pH paper to test for contrast?!!!:tongue:

    Ray
     
  16. Photo Engineer

    Photo Engineer Subscriber

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    Ray;

    Sorry, mistake.

    You use pH paper to test for the desired pH value and you test the adjusted developer for the desired contrast. Wow what an error. Thanks.

    However, once you establish the pH you want, then pH paper can be used to "test for the desired contrast".

    Thanks for the correction.

    PE
     
  17. Alan Johnson

    Alan Johnson Subscriber

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    Benzotriazole can be replaced by 10x its weight of Potassium Bromide,at least in some formulas.GW Crawley suggested replacing the original 50mg/L Benzo in FX-37 by 500 mg/L KBr, as the bromide is easier to dissolve.Presumeably the replacement works the other way round.
     
  18. BradS

    BradS Subscriber

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    Can you elaborate on this? I think I understand but, I want to make sure...in particular, what is meant by 'stability'?

    Is it the...hmmm, say the activity of the developer that is unstable over time (as in the shelf life time) ? Or, is it simply "photographic properties" generally that are unstable over time (again, I'm assuming storage time but, perhaps, even over the development time?)

    Let's take an example...

    Compare the published D-23 receipe to say, D-23 plus 5grams per liter Borax (I believe the Borax actually increases the ph in this case but could be wrong).


    tia.

    Brad.
     
  19. Photo Engineer

    Photo Engineer Subscriber

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    Brad;

    Firstoff, the major change is due to absorption of CO2 from the atmosphere which drops the pH as the developer keeps. This is due to the following: Borate and Carbonate love to buffer in the range of about 9.5 - 10.5 depending on the mix you have going. More Borate or Carbonate don't change pH much, this would only change buffer capacity, so you need to add something like Sodium Hydroxide.

    Now, this increase takes us away from the buffer point of Borate or Carbonate, and so the developer is less stable from a pH (and therefore contrast) standpoint and our goal is higher contrast.

    To get a high pH developer, you use Trisodium Phosphate as buffer and this works at about 11 - 11.5, but then the developer is still not as stable as you want due to Carbon Dioxide in the air.

    That is about it, stability to pH changes is what I referred to, and since high pH is the element I suggested, you can retain activity simply by checking and adjusting the pH if it starts to drift. This is, in fact, what is done to control E6 color developer (pH ~11 with phosphate) and Kodachrome developers when they drift. They are essentially high contrast color developers that force the reversal development to completion.

    The high contrast B&W developer, D8, has almost 40 g/l of Sodium Hydroxide and it is loaded with Hydroquinone. Both are known as being able to yield high contrast results. It has however, low buffer ability when compared to most other developers.

    PE
     
    Last edited by a moderator: Apr 23, 2008
  20. BradS

    BradS Subscriber

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    Oh, I was over analyzing it (again). Thanks for the explanation.
     
  21. Ryuji

    Ryuji Member

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    This may sound very disappointing, but it is very difficult, almost impossible, to increase contrast and decrease density at the same time, with a same emulsion and exposure.

    Benzotriazole _may_ *slightly* increase contrast, but it only do so in the very lightly exposed areas (shadow in negative, highlights in prints) and not in the rest of the curves. If you use too much benzotriazole, what is most likely to happen is to require longer development time and/or greater exposure, without changing the curve shape much except for the toe region.

    Crawley did publish interesting formula and his commentaries on them. I have tested a number of antifoggants, desensitizing dyes and KBr in various contexts, but in my experience none of them is a magic bullet. The reality is that if you try to change one thing and you lose something else. In almost all cases, I got the best results by balancing the developing agents, sulfite content, and the pH, while keeping the KBr and other antifoggants well within the reasonable and normal range. In particular, I did not find any magical effect in using Pinakryptol green, Pinakryptol yellow and various derivatives of phenosafranine in developer solutions.
     
  22. FRANOL

    FRANOL Member

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    In almost all aspect of life:wink:
     
  23. Rich Ullsmith

    Rich Ullsmith Subscriber

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    So it is my understanding that with benzotriazole as a restrainer, its concentration in the pan will decrease with each processed print? Is this correct?

    I use it in lith instead of KBr, on the assumption that if I dump and replace half the contents of the tray, then I will have dumped half the amount of bzt I had in there. If the developer was to my liking, I know how much bzt to replace. Br- levels are always increasing, so I have no way of knowing how much to replace.

    If bzt levels decrease with use, I guess I have been chasing my tail and gotten lucky from time to time. Is my thinking correct here?
     
  24. Photo Engineer

    Photo Engineer Subscriber

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    Yes Rich, your thinking is correct. BTAZ concentration decreases along with developing agents, alkali and sulfite. Halides can increase or stay the same depending on developer and paper.

    PE
     
  25. NB23

    NB23 Member

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    Where can I buy Benzotriazole?

    I have a few boxes of Agfa FB that are fogged. Potassium bromide
    doesn't help and I can't find Benzotriazole...
    Any help appreciated.
     
  26. Photo Engineer

    Photo Engineer Subscriber

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    Try the Photographers Formulary. It is listed in a banner ad here.

    PE