Superadditivity in developers - and beyond

Discussion in 'B&W: Film, Paper, Chemistry' started by Photo Engineer, Apr 29, 2007.

  1. Photo Engineer

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    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. Keith Tapscott.

    Keith Tapscott. Member

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    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. Photo Engineer

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

    PE
     
  4. Keith Tapscott.

    Keith Tapscott. Member

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    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?
     
  5. Photo Engineer

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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.
     
  6. gainer

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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.
     
  7. Photo Engineer

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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
     
  8. RidingWaves

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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.
     
  9. Photo Engineer

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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
     
  10. Keith Tapscott.

    Keith Tapscott. Member

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    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.
     
  11. Photo Engineer

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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
     
  12. Keith Tapscott.

    Keith Tapscott. Member

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    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.
     
  13. gainer

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    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.
     
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  15. Photo Engineer

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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
     
  16. gainer

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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.
     
  17. phritz phantom

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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)
     
  18. Photo Engineer

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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
     
  19. gainer

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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?
     
  20. Photo Engineer

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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
     
  21. gainer

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    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.
     
  22. gainer

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    I got the following ideas after reading pertinent passages of "The Theory of the Photographic Process", third edition, Mees and James, editors.

    In the pH range where ascorbic acid is not actively a developer, it behaves much like a sulfite. It has been shown (p. 367 of the reference) to be not significantly different from sulfite in affecting the developing activity of metol at pH 8.7 when the molar concentrations of the sulfite and ascorbic acid are the same. The mechanisms by which they work are different, the sulfite by forming the sulfonate of metol and the ascorbic acid by reducing oxidized metol to its original state. It would seem, then, that either sulfite or ascorbate ought to serve the same theoretical purpose in a superadditive mixture of, say, metol and hydroquinone.

    Another property shared by sulfite and ascorbate is the abiliy to reduce the latency period of hydroquinone. It would seem that by most theories of the superadditivity phenomenon, either sulfite or ascorbate should be able to do the job. The required amount of either is quite small compared to the amount of sulfite commonly used. Thus, the combination of metol, ascorbate and hydroquinone should not be considered as a 3-agent developer when the minimum amount of ascorbate to achieve superadditivity is used, any more than the combination of metol, sulfite and hydroquinone is. There is usually little need to remove the sulfite, but when formulating a developer for staining, the less sullfite, the more intense the stain.

    When we substitute ascorbate for hydroquinone in a PQ or MQ developer, we can leave out the sulfite and still have superadditivity because part of the ascorbate takes its place in restoring the phenidone or the metol. In this case, the developer does not stain the image.

    Pp 289 and 304 of the reference will also be of interest.
     
  23. Photo Engineer

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    I believe that this is correct Patrick, and Ascorbate also loses its ability to cross oxidize. Therefore it cannot work as an ET developer or in a superadditive manner as pH goes down.

    This is why I wondered what the sulfite did to pH in your previous post. If pH went up, likely the activity of ascorbate would increase (IIRC, you used ascorbate. I am sorry but I didn't look at that post to refresh my memory).

    In any event, ascorbic acid is pH sensitive as you describe.

    PE
     
  24. gainer

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    Ah Ha! The developer under study was a PQ-TEA solution to which I added either nothing, sodium sulfite or sodium ascorbate. The activity of PQ + TEA + water was very low, about what one might expect from the phenidone alone at 0.02 g/l. The activity took a leap when I added about 8 g/l of sodium sulfite.
    Starting over with just the PQ-TEA in water, the activity took an even greater leap when I added 4 g/l of ascorbic acid as the ascorbate.
    In other words, it seemed to me that ascorbate and sulfite were performing about the same task in a PQ type of developer.
    This information is not world shaking, but would have consequences for those who are trying to get the most image stain possible out of catechol or who want to put a complete developer in a glycol or TEA solvent. We have seen it work in Pyrocat MC. Perhaps it has some bearing on the theory of synergism insofar as the replenishment of the "main" agent can be done by the sulfite or by ascorbate instead of the "secondary" developer. It is not possible, at least by me, to determine which is which. A clue is the variation of the activity of metol when either ascorbate or sulfite is added to the solution, where it appears that either one has the same effect as replenishing the metol.
    Anyway, it gives an old codger something to keep his brain going.
     
  25. Photo Engineer

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    Patrick;

    It may be that the activity is linked to a pH change though. Do you have a way to check?

    PE
     
  26. gainer

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    Perhaps my best bet would be to start over with an MQ-borax solution in water, like the basis of d-76 without sulfite. With enough borax, the buffering ought to be strong enough to minimize pH changes from no additive to either sodium sulfite or sodium ascorbate. In either case, I would be using the same molar concentration as was used in the experiments I referred to before. However, if there is a change in pH, it should favor the sulfite as sodium ascorbate solution itself is not likely to be higher than 7.6 according to Merck.

    I do not have a way to check pH. I will search the local swimming pool supply places for pH indicators that might narrow it down, at least for differential readings. I am 50 miles from the nearest moderate sized cities and 100 miles from the next size up. Otherwise it's internet or mail, and I'm too impatient.