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    Photo Engineer's Avatar
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    Superadditivity in developers - and beyond

    Well, here is another in a series of information on B&W process chemistry design.

    Everyone seems to be aware of superadditivity in developers, so I will go beyond that to something new.

    Kodak films contain a unique development accelerator. I have used one of them here in my emulsions. It is so specific, it works with one emulsion but not with 3 other formulas, one just a tiny variation of the one it works with. With an accelerator in the paper formula, I gain about 1 stop in speed and about one grade in contrast on average. Using them in developers would cause similar variations between emulsion types and similar variations in the improvements observed. They are difficult to control and are often specific to the emulsion.

    However, this does not rule them out. These compounds work by swelling the gelatin about 2x over the normal amount allowing faster reaction and growth of the silver metal particles. I have never tried them in the developer myself, just coatings, but I have heard of them working. In fact, someone mentioned one of the simplest and most generic here. It is urea. Since it increases swell, the film becomes more tender though. I may mention the other here sometime, but if someone picks up the hint, you will find reference to it here on APUG. Try and find it. If you catch it, put a scholarly feather in your cap, post it and I will discuss it more fully here.

    HINT: This common material has been mentioned here for giving heavy dark spots or increased development on negatives. That is because it is accelerating development.

    Another 'beyond' is the use of silver halide solvents in fine grain or high acutance developers. People are afraid to use them for fear of dichroic fog. I must say that most films today have ingredients that prevent large scale formation of dichroic fog, but you can see this fog if you use high levels of solvent or if you use a strong solvent. Kodak has additives for developers (Microdol-X) and other films for preventing this sort of fog. They are unique. One is published. Put another feather in your cap if you find either and post it. Then we can discuss it further.

    Enjoy.

    PE

  2. #2

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    Quote Originally Posted by Photo Engineer View Post
    Well, here is another in a series of information on B&W process chemistry design.

    Everyone seems to be aware of superadditivity in developers, so I will go beyond that to something new.

    Another 'beyond' is the use of silver halide solvents in fine grain or high acutance developers. People are afraid to use them for fear of dichroic fog. I must say that most films today have ingredients that prevent large scale formation of dichroic fog, but you can see this fog if you use high levels of solvent or if you use a strong solvent. Kodak has additives for developers(Microdol-X) and other films for preventing this sort of fog. They are unique. One is published. Put another feather in your cap if you find either and post it. Then we can discuss it further.

    Enjoy.

    PE
    AFAIK, there are Kodak patents that cite the use of an anti-stain agent for preventing dichroic fog. One of these is Benzoresorcinol (2,4-dihydroxybenzophenone). This or similar components may even be used in a wide range of commercial developers besides the Kodak products.
    Anti-Stain agents are mentioned along with two E.K. Patents by Richard W. Henn on Ryuji Suzuki`s Silvergrain website.
    Is this one of the ingredients that you wish to discuss?

  3. #3
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    This is one. It is not (AFAIK) in current use.

    PE

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    Quote Originally Posted by Photo Engineer View Post
    This is one. It is not (AFAIK) in current use.

    PE
    Another one mentioned there, is Chlororesorcinol in which Henn describes it`s use with Kodak D-25 replenished with DK-25R for processng Verichrome Pan. Which other components are used in modern developers?

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    Well, those are rather old and not used in modern formulas, but the benzophenone is the most prominent. I'm really not much familiar with the chlororesorcinol.

    I'll wait and see if anyone else turns it up.

    PE.

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    The superadditive behavior of ascorbic acid with phenidone , Metol, p-aminophenol and perhaps others is a bit mysterious to me. Hydroquinone seems to require sulfite to achieve similar synergism, while ascorbate does not. It is said the ascorbic acid is a surface developer and that the function of sulfite is to break the surface barrier. I have found that a small amount of ascorbic acid in, say, a Metol-hydroquinone solution seems to be capable of at least as much superadditivity as the MQ solution with sulfite. It will be a staining developer if used without sulfite, as would the combination of Metol-pyrogallol-ascorbate or Metol-catechol-ascorbate, or p-aminophenol-catechol-ascorbate. I only know these things from experiment. If the ascorbic is more an antiozidant than a developer in these combinations, thus literally taking the place of sulfite, I do not know. It does work, as anyone who has used Pyrocat MC can attest.
    Gadget Gainer

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    Patrick;

    Sulfite also drags the oxidation of HQ to the right by scavenging the quinone by generating HQ monosulfonate which itself is a weak developer.

    But, as a number of people have said, the use of more than two developing agents is a real reach. I know that Haist has said that, and probably Henn and Lee as well.

    BTW, I have also made mention elsewhere of ETA developers. They are distinguished from superadditive developer combinations by having the pH adjusted to be optimum for the primary developer. The primary developer is present at very low concentrations. The other developer is not really active under these conditions except to regenerate the primary developer. These are unique and AFAIK there are not currently on the market.

    PE

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    Sodium Chloride? Fun game BTW. I don't really care if I'm wrong or not, because I know I'll learn from any answer posted.

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    That is a good answer. It is actually the silver halide solvent used in Microdol-X that tends to cause the dichroic fog and that fog is prevented by an additive like the benzophenone mentioned above.

    There are others though. I'll eventually post a few.

    PE

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    Quote Originally Posted by Photo Engineer View Post
    That is a good answer. It is actually the silver halide solvent used in Microdol-X that tends to cause the dichroic fog and that fog is prevented by an additive like the benzophenone mentioned above.

    There are others though. I'll eventually post a few.

    PE
    I think it`s also used in Ilford Perceptol which is probably a Microdol clone. The old super-fine grain PPD developers had a reputation for poor speed yield and mushy definition, I believe that these were supplanted with DK-20 (Ilford ID-48 was similar) which contained Sodium Thiocyanate.
    This was also a silver solvent, but it too fell from favour due to causing dichroic fog and was superseded by Microdol and then Microdol-X.
    With modern film technology, it seems unusual these days to use a developer that yields finer grain than those of the D-76 type as modern films already very fine grained.
    Perhaps it`s more desirable to use a developer that keeps grain in check with films of ISO 125 and above that also exploits the full ISO film speed and to use a high definition developer with modern ISO 100 films and traditional slow emulsions.

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