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  1. #1
    Photo Engineer's Avatar
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    Ammonia or Ammonium salts in emulsion making

    I have gotten a number of E-mails and PMs regarding the use of Ammonia or Ammonium salts in emulsion makes.

    It seems that the queries were based on a post made elsewhere which quotes T. Thorn Baker as follows:

    "A small quantity of ammonia should always be present in either the salts or the first silver solutions, otherwise clots or agglomerates of precipitates may be formed, which will cause black spots on development without exposure..."

    'Photographic Emulsion Technique', 1st Edition, 1941, by T. Thorne Baker. p 78.

    I donít have the first edition handy, but in the second edition a similar quote is found on p 221 and rather limits this comment to paper emulsions or Cl/ClBr and Br types and goes on to give the conditions which cause pepper grain such as the wrong gelatin, too little gelatin, incorrect concentration of ingredients and etc.

    In other words, Baker concedes that most emulsions donít need any Ammonia or Ammonium salts as long as the formula is a robust one. You see, experimentation is expensive and thus many early formulas were taken ďas isĒ even if they were less than optimum, and quite a few experimenters found that Ammonium ion was a quick fix for any troubles that they ran into.

    With more experimentation, Baker and others found that robust formulas avoided this problem. In fact, AJ-12 and the emulsion that Mark Osterman and I used in the recent workshop are both quite robust and need no Ammonia whatsoever. And, virtually none of the hundreds of emulsion that I worked with at Kodak used Ammonia in any form.

    It should be added that Ammonium ion is less effective at an acid pH, and an emulsion with Ammonium salts tends to be more acidic. Ammonia also has a strong odor if used in an alkaline environment and finally, without rigid control, Ammonia can cause severe fog. So, use of the Ammonium ion is not needed in almost every case I know of and the statement in Baker in his second edition is more realistic. Considering the above quote, Ammonia, used with the Silver Nitrate results is a more alkaline and complexing environment, while Ammonium salts in the kettle at the start of the emulsion precipitation result in a more acidic and less complexing environment. Either way, Ammonium ion was a quick fix for faulty emulsion design and is rarely used at Kodak. If a solvent is used, either other methods or solvents are used to perform the digestion. Ammonium ion in any form and at any pH, puts one on the precipice of fog!

    So, this quote may have been taken out of context or Baker may have revised his thinking. Either way, it is wrong to assume that Ammonium salts of any sort are needed to preven pepper graon.

    PE

  2. #2
    Hexavalent's Avatar
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    The only time I've had 'pepper' appear was with a quick pptn with inadequate stirring. Keeping the emulsion as fast as possible without "sucking air" completely eradicated those nasty little black spots. Using chemistry to solve a mostly 'mechanical problem' seems like a bit of a kludge.
    - Ian

  3. #3
    kb3lms's Avatar
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    Hi PE,

    What do you mean by a "robust" formula? What makes it robust?

    I've got Baker's 1st edition but not the second.

    -- Jason
    All this has happened before, and all this will happen again.

  4. #4
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    Jason, a robust formula is one that does not need Ammonia or other "crutches" to make it work. As Ian says, using chemistry to solve a mechanical problem is not right for his case.

    I'll give another. The Axo type emulsion that is in my book works well with no pepper grain, and you can make it at 100 g - 3000 g scales with no problems as long as you supply correct mixing. If you go over 1 L for example, you have to use a mechanical stirrer and the magnetic mixer both to get proper mixing. Otherwise, you risk burning the gelatin on the bottom, bad mixing at the top and pepper grain. Deviation from the Azo type formula will cause problems.

    In the case of Mark Osterman's plate emulsion, we have collectively made it over and over with no pepper grain and no Ammonium salts. It works perfectly as written. It is a robust formula. Deviation from the written formula will cause problems.

    These are robust formulas achieved by lots of experimentation.

    The Kodabromide / Brovira type formula in my book is robust.

    Now, take all of these formulas and consider this, when a significant deviation occurs, pepper grain will appear. So, lets look at a poor formula for you to compare with. Make the Azo type emulsion with 1/2 of the amount of gelatin specified. You get just about the same results but with load of pepper grain. Or, take the Kodabromide / Brovira type formula and move 1/2 of the water from the Silver Nitrate to the Gelatin side and then make the emulsion. It is totally unusable due to pepper grain and aggregate. These two emulsions have been made stable without resorting to a chemical "trick".

    I hope these examples from my experience help.

    PE

  5. #5
    kb3lms's Avatar
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    Sounds like another word for robust might be "debugged"! But I get the idea. I've got to go back and read up on the role of ammonia because I do not yet understand it.
    All this has happened before, and all this will happen again.

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    Yeah, debugged is right!

    Thanks.

    PE



 

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