restraining and reducing: the role of bromide

Discussion in 'B&W: Film, Paper, Chemistry' started by David Lyga, Mar 26, 2013.

  1. David Lyga

    David Lyga Subscriber

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    Two seemingly simple questions I have:

    First: What is the precise role of bromide in Farmer's Reducer?

    Second: With regard to restrainers: Is there ever a circumstance whereby potassium bromide is preferable to benzatriozole?

    - David Lyga
     
  2. Ian Grant

    Ian Grant Subscriber

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    First bromide isn't used in Farmers reducer, although it won't hurt if it's there/

    Second Benzoriazole produces cold tones with prints and so shouldn't be added to warm tone developers.

    Ian
     
  3. David Lyga

    David Lyga Subscriber

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    Ian, the formula for Farmer's reducer contains bromide. I do not use it but it is there. Am I incorrect? (Thank you for the warm tone exception.) - David Lyga
     
  4. Gerald C Koch

    Gerald C Koch Member

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    I think you mean re-halogenating bleaches. Potassium bromide is used so that when the silver is oxidized it is converted to silver halide again. Such a bleach may be used in connection with an intensifier.

    Ag0 - electron --> Ag+ + Br- --> AgBr
     
  5. Ian Grant

    Ian Grant Subscriber

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    No true, Farmers reducer is a two part reducer mixed just before use.

    Rarmers Reducer

    Part A
    Sodium Thiosulphate 40g
    water to 1 litre

    Part B
    Potassium Ferricyanide 19g
    Water to 250ml

    To use 1 part B + 4 parts A

    Make up to 32 parts with water

    ie 10ml B + 40ml A + 270ml Water = 320ml working solution.
    It has a very short life


    A very lazy way is to use a rehalogenating bleach used for toning with some fixer, however this is faster working and not as controllable and you shouldn't use a Rapid fixer.

    Ian
     
  6. Rudeofus

    Rudeofus Subscriber

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    Yes, if cost and trivial availability mean anything to you :whistling:
     
  7. David Lyga

    David Lyga Subscriber

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    Not true, Ian, for print reducer. This 'unblinking eye' site (upper right of page) shows the reducer for prints: http://unblinkingeye.com/Articles/Developers/Formulas/formulas.html

    But, Ian, the negative reducer is as you state: no bromide. I wonder why the difference? - David Lyga

    And Rudeofus: 'trivial availability' has to be conquered but once in one's lifetime: a bit of benzotriazole goes far and can be kept permanently in powder form if airtight. - David Lyga
     
  8. Ian Grant

    Ian Grant Subscriber

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    Farmer's Reducer has never had Bromide in the official formula, and it's been sold by many companies. Agfa Ansco (GAF) 310 (which I listed above), Kodak R-4a and R-4b, and Ilford IR-1 are all named as Farmer's Reducer and essentially just slight variations in terms of concentration but only use Ferricyanide and Sodium Thiosulphate.

    So there's a mistake on that website.

    Ian
     
  9. Jim Noel

    Jim Noel Member

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    I agree with Ian. I have been at this business of analog photography fro more than 70 years, and I have never seen the formula shown in "Unblinking Eye". Farmer's Reducer is a simple two solution formula mixed just prior to use.

    Jim
     
  10. cliveh

    cliveh Subscriber

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    David, are you confusing Farmer's reducer with sepia tone bleach?
     
  11. Greg Davis

    Greg Davis Member

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    The sepia tone bleach I have purchased from Kodak contains only Potassium Ferricyanide, so it just part A of Kodak's Farmer Reducer.
     
  12. Ian Grant

    Ian Grant Subscriber

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    Are 110% sure, it not viable.

    Ian
     
  13. Greg Davis

    Greg Davis Member

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    What? Are you saying that it isn't viable, or not available? While Kodak doesn't sell it anymore, some stores here still have old stock on the shelves. The bleach portion is packaged separately and is clearly labeled as potassium ferricyanide, as is one of the two packets that make up the Kodak Farmers Reducer that I have on my shelf.
     
  14. cliveh

    cliveh Subscriber

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    The Ilford manual states (not that you should believe anything you read) –
    Stock bleaching solution
    Potassium ferricyanide 25g
    Potassium bromide 25g
    Water to make 250g
    I have used this and it works fine.
     
  15. David Allen

    David Allen Member

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    The formula that I have for Farmer's Reducer is:

    Stock A:
    Potassium Ferricyanide 19 g
    Water 250 ml

    Stock Solution B:
    Sodium Thiosulfate 240 g
    Water 1 litre

    Mix 30 ml of Solution A together with 120 ml of Solution B and then add water to make 1 litre of working solution.

    A popular variant of the Farmer's Formula purely for use with prints as it is a re-halogenating version of the reducer (which means that, if you over bleach the print you can return it to a developer and build up the density once more).

    Stock A:
    Potassium Ferricyanide 64 g
    Potassium Bromide 30 g
    Water 250 ml

    Stock B:
    Sodium Thiosulfate 120 g
    Water 500 ml

    For controllable use you mix 7.5 ml of Stock A together with 180 ml of Stock B and add 750 ml of Water.

    The formula that I have for a PROPORTIONAL reducer is:

    Stock A
    Potassium Ferricyanide 7.5 g
    Water to make 1 liter

    Stock B:
    Sodium Thiosulfate 200 g
    Water to make 1 liter

    You place your print/negative in solution A for 2 to 5 minutes and then you place it in solution B for 5 minutes followed by a very thorough wash.

    The Adams' formula that I have used most myself (albeit long ago when I had no choice but to use old paper) to clean up veiled/very slightly fogged highlights or to boost the whites of people's eyes in commercial portraits, etc):

    Stock A
    Thiourea 15 g
    Sodium Thiosulphate 700 g
    Water 1 Litre

    Stock B
    Potassium Ferricyanide 75 g
    Water 250 ml

    To make a working stock (does not keep long) you add 5 parts of Solution A to 14 parts Water (Working Bath A) and then combine Working Bath A with an equal quantity of Stock B.


    Many people get happily by with just using the simple Farmer's Formula but I am aware of many friends who have been plagued by intermittent yellow staining / over bleaching / etc who have moved to either the Potassium Bromide variant of the Farmer's Reducer or, more often, to Adams' Thiourea formula.

    Hope that helps.

    Best,

    David
    www.dsallen.de
     
  16. Rudeofus

    Rudeofus Subscriber

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    Am I correct that if one uses the Bromide+Thiosulfate version of Farmer's reducer, that the print must be fixed afterwards?
     
  17. Ian Grant

    Ian Grant Subscriber

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    You should re-fix after any reducer. The problem is the ferricyanide breaks down the thiosulphate so you might not completely remove the bleached silver without re-fixing.

    Ian
     
  18. Doremus Scudder

    Doremus Scudder Member

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    Yes, anytime the image silver is bleached or rehalogenated, it must be fixed out or it could (will) cause staining later.

    FWIW, I think we need to distinguish between ferricyanide/thiosulfate bleaches (Farmer's, etc.) and the rehalogenating bleaches, which contain bromide.

    What is clouding the issue, I believe, is that you can add thiosulfate to rehalogenating bleaches to speed up the bleaching process (creating a sort of hybrid). However, I use a simple potassium ferricyanide/potassium bromide rehalogenating bleach for both negatives (bleach/redevelop) and prints (both local and overall bleaching) with good results. No thiosulfate at all in the process. I find it more controllable (not to mention reversibly to a certain extent) than Farmer's Reducer.

    For David,

    Bromide in the bleach makes a rehalogenating bleach, as Gerald points out. I works similarly to other ferricyanide bleaches but can be reversed to some extent and some, like myself, find it more controllable.

    Bromide in developers acts as a restrainer and helps prevent fog. It warms image tone a bit in print developers.

    Benzotriazole is an organic anti-foggant, works differently chemically than bromide, but accomplishes much the same thing; a reduction in fog. I cools image tones in prints somewhat.

    Many fine-tune the proportion of bromide and BZT in their print developers to control image tone.

    I'm not sure of the differing roles of bromide and BZT in formulating negative developers. I suspect it is more complex than my current knowledge. I do know that phenidone developers do not react as well to bromide in the formula and, therefore, BZT is usually used as a restrainer if one is needed (the same would apply to print developers also I suppose).

    Best,

    Doremus


    www.DoremusScudder.com
     
    Last edited by a moderator: Mar 27, 2013
  19. David Lyga

    David Lyga Subscriber

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    Thank you all, especially David Allen, Ian Grant, and Doremus Scudder. You have helped to clarify this, especially with the re-halogenation part.

    If there are further comments, speak. - David Lyga
     
  20. tars

    tars Member

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    Hi, Doremus

    I want to slightly lighten some parts of my prints on FB warmtone paper and I want a simple reducer formula for that. What's your bromide/ferricyanide formula and how do you use it? Also, if I use only a ferricyanide solution and then wash and fix, will the prints be more prone to strains? (I will selenium tone them subsequently in strong KRST solution for long time).

    Thank you in advance :smile:
     
  21. Doremus Scudder

    Doremus Scudder Member

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    Tars, I start with a double 1% solution, i.e., 1g ferricyanide and 1g bromide per liter. I keep solutions of both on hand: a 10% ferricyanide solution and a 3.4% potassium bromide solution. I make a liter of bleach by starting with 10ml of the ferricyanide solution and 30ml of the bromide. (For local bleaching, I mix up smaller amounts in the same proportions.) This is rather weak, and I don't hesitate to add more of both if needed; its very subjective.

    As for toning: I have found that heavily bleached areas can selenium tone differently, but that it depends on the paper many times just what happens. I try to avoid bleaching really heavily and tone lightly when I think I might have problems (by that I mean toning a long time in a weaker toning solutions so that I can pull the print quickly if I notice any change in toning from bleached to non-bleached areas. I also time the bleaching so that I can avoid the split-toning in subsequent same prints.).

    Toning will almost certainly be different if you overbleach and then return the print to the developer to save it. Tone very lightly if you do this.

    If you just use ferricyanide alone, the bleaching will be slower. Often, you need to help it out a bit by adding fixer, in essence, making Farmers reducer. Sodium or ammonium thiosulfate will both work, but the ammonium thiosulfate reacts a lot more strongly with the ferricyanide and is often harder to control).
    I used to bleach right after the first fixing bath with plain ferricyanide; the amount of rinse I gave the print before bleaching controlled the amount of fixer still remaining in the emulsion and, therefore, the activity of the bleach.

    Bleaching is an art and takes experience, but is a great tool. If you are just starting out, be prepared to ruin some prints in the learning process. I still ruin some, but I consider bleaching a print manipulation, and I toss a good number of prints with inadequate dodgine, burning or exposure too.

    Best,

    Doremus


    www.DoremusScudder.com