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  1. #11
    Photo Engineer's Avatar
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    Well, among others, Kodak used ethylene diamine as a silver halide solvent that was mild and did not cause excessive dichroic fog. They also have used thiocyanates as you mention for solvents, along with other organic solvents that repress dichroic fog just as the benzophenone does.

    Lets consider this one solved. You all get a feather of some sort or another for really good answers. Thanks. Additions are still welcome though as there are more specific examples out there.

    PE

  2. #12

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    Quote Originally Posted by Photo Engineer View Post
    Well, among others, Kodak used ethylene diamine as a silver halide solvent that was mild and did not cause excessive dichroic fog. They also have used thiocyanates as you mention for solvents, along with other organic solvents that repress dichroic fog just as the benzophenone does.

    Lets consider this one solved. You all get a feather of some sort or another for really good answers. Thanks. Additions are still welcome though as there are more specific examples out there.

    PE
    Ilford had a product called ID-11 Plus which was said to be D-76 with the addition of Cinnamic acid and also a mercaptan, although I must confess that I don`t know what the functions of these components are, perhaps you could enlighten us.
    Also, BKA sell a product called Crone C additive which is supposed to enhance the performance of D-76/ID-11 although not something that I`ve tried and not available over here in the UK.

  3. #13
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    Quote Originally Posted by Photo Engineer View Post
    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
    OK, but try the combination of Metol-hydroquinone without sulfite. How much superadditivity do you get? Now add a very small amount of ascorbate and see what happens. While the thought of a developer without sulfite is repugnant to some, it is very handy to have a sulfite-free staining developer all of whose components are soluble in glycol. Granted, HC110 solved that problem with an organic sulfite, but it is not a staining developer. Sulfite in rather small concentration prevents staining in catechol or hydroquinone developers. It takes more to eliminate staining by pyrogallol, but it can happen. If the stain is not desired, sulfite added to the working solution will prevent it, and there is a wide latitude in the measurement of its quantity.

    A superadditive mixture of Metol or Phenidone with ascorbate is obtained without sulfite and is non-staining.
    Gadget Gainer

  4. #14
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    Patrick;

    I agree with all you said. My comments throughout are directed entirely to non-staining developers. I feel that you can get results as good with 2 developing agents though and that adding a third is, to an extent, redundant based solely on comments by Haist and based on his work, that of Henn and also Lee.

    Sulfite merely adds to the overall equation by sopping up the quinone and regenerating a milder developing agent and putting it back into the pool of avialble developing agent.

    The ratio of activity of HQ to HQ-monosulfonate is about 1:25 or larger.

    Keith, mercaptans tend to be silver halide solvents and at the same time can act as such while lowering or eliminating the tendancy to form dichroic fog. I'm not sure of the cinnamic acid though unless it is there to mask the odor of the mercaptan. Cinnamic acid smells rather nice IIRC, even as a salt, but generally mercaptans stink. Oil of skunk is t-butyl mercaptan BTW just to put it in perspective.

    PE

  5. #15
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    Non sequitur: there once was a plan to use skunk oil (a mercaptan) as a weapon of war. It was supposed to keep oriental opponents from associating with their compatriots who had been sprayed with it.
    Gadget Gainer

  6. #16

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    do you mean film speed or development time?
    i don't care much about the time it takes to develop my film/paper. but gaining one stop in film speed, i would be very interested in...

    i'm using selfmixed xr-1 for my low light photography. which already has the superactivity of phenidone plus hydroquinone. so would adding urea or the secret ingredient allow me even higher asa-ratings? (normally i use trix or hp5 at 800 - 1600asa)

  7. #17
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    I have seen some ingredients that boost speed, some that enhance development time, and some that do both. I've seen some that also cause fog. The ones added to developers can do any, all or none depending on emulsion.

    PE

  8. #18
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    I did the experiment that I suggested. I mixed a batch of PQ-TEA, 50 g hydroquinone + 1 g phenidone in TEA to make 500 ml. It's handy to have around anyway. So far I have just done snip tests. First, 1 + 50 parts of water, 2 minutes. As you might expect, some darkening. Adding a teaspoon of sodium sulfite to 500 ml of this solution produced, also as you might expect, a dramatic increase in activity. Starting over with the PQ-TEA solution as before, adding 1 gram of sodium ascorbate produced an increase in activity, but not as great as the sulfite, but a teaspoon of sulfite is about 8 grams, or roughly .05 moles. I'm headed back to the darkroom to try the ascorbate again. 1 gram is a little more than 1/200 mole. I am considering the ascorbate as an antioxidant. As such, should I count a molecular weight of it as the same as or different from sodium sulfite?
    Gadget Gainer

  9. #19
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    MW is MW Patrick.

    How did the sulfite change the pH? That might affect the activity more than the sulfite in and of itself.

    PE

  10. #20
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    Quote Originally Posted by Photo Engineer View Post
    MW is MW Patrick.

    How did the sulfite change the pH? That might affect the activity more than the sulfite in and of itself.

    PE
    Yes, of course, but one molecular weight of ascorbic acid, IIRC, will take up two molecular weights of oxygen while one molecular weight of the sulfite takes up one.

    Meanwhile, I added two grams of ascorbic acid as ascorbate to 500 ml of the PQ-TEA. The ascorbate is near neutral in pH. The effect on density was much greater than the effect of the sulfite.

    These experiments are not intended to be as quantitative as might be, but to give some idea of relative effects.

    I have read what I could find on the subject of superadditivy, starting in my NASA days with an American compilation of Russian compilations of American compilations, and have not seen very much said about the role of sulfite. I do not think the MQ or PQ synergisms can exist without sulfite. I know the MC and PC synergisms do exist without sulfite.

    I could and probably should do some comparisons between the individual developing agents. Synergism will be shown when the effect of the sum of two components is greater than the sum of the effects of the individual components. I can include the effect of sulfite. It's times like these when I wish I had assistants I could assign to do the actual work.

    I have a feeling it has been done.
    Gadget Gainer

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