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  1. #11

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    I agree you are right about superadditivity of phenidone glycin described in this thread:
    http://www.apug.org/forums/forum37/9...xperiment.html
    Mason p29 does say phenidone glycin is superadditive but does not say it is of poor utility.
    I found glycin pyrocatechol is superadditive. In Pyrocat HD 2g/L phenidone can be replaced by 10g/L glycin (25 g/L precipitates out after a month or so).

    Regarding US Patent 5998110,results in table 1 and table 2 suggest metol alone does not work, metol + Dimezone S does.,results in table 5 that Dimezone S with very little metol does not work very well.They seem to conclude superadditivity of metol Dimezone S when developing X-ray film 20seconds 35 degrees C.

    I think it is speculation to conclude superadditivity at normal temperature 20C when developing ordinary pictorial film.

  2. #12

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    have you any information about temp treshold for superadditivity effect?

  3. #13

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    Quote Originally Posted by Alan Johnson View Post
    Regarding US Patent 5998110,results in table 1 and table 2 suggest metol alone does not work, metol + Dimezone S does.,results in table 5 that Dimezone S with very little metol does not work very well.They seem to conclude superadditivity of metol Dimezone S when developing X-ray film 20seconds 35 degrees C.

    I think it is speculation to conclude superadditivity at normal temperature 20C when developing ordinary pictorial film.
    But superadditivity is normally a function of the side products from one developer causing regeneration in the other, right? I'm no chemist, but in my understanding the reason that metol and the phenidone "family" aren't thought to be superadditive is that neither one can produce anything that regenerates the other. Why would that depend on temperature, or on the difference in emulsions between x-ray and pictorial films?

    By the way, my point with perpetual motion machines was just that "it's in a patent" is not by itself a strong indication of something being correct. Let's not automatically write off the possibility that the results in this case were just wrong---though again, based on the inventor's credentials, I think it's more likely that there's something going on here that we don't understand.

    -NT
    Nathan Tenny
    San Diego, CA, USA

    The lady of the house has to be a pretty swell sort of person to put up with the annoyance of a photographer.
    -The Little Technical Library, _Developing, Printing, And Enlarging_

  4. #14

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    my understanding of superadditivity two agent A and B is that D(A+B) strong great than D(A)+D(B). here D(x) - density obtained by agent x. I think that x-ray emulsion isn't very different from generic BW emulsion.

  5. #15

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    Quote Originally Posted by Relayer View Post
    my understanding of superadditivity two agent A and B is that D(A+B) strong great than D(A)+D(B). here D(x) - density obtained by agent x.
    This isn't really true. If you read Mason, he speaks of velocity and not density. It is a matter of kinetics. Any increase in density is caused by the increase in activity. As a chemistry instructor of mine was fond of saying, "It is not the trees shaking that makes the wind blow but the wind that makes the trees shake."
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  6. #16

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    In "The Theory of the Photographic Process" by Mees and James is a section on superadditivity but I did not find any mention of temperature effects.However, James found ".. if an oxidation product of the first developing agent inhibits development,regeneration may effectively remove this this inhibiting product from the grain by converting it to active developer".

    It is quite well known that the oxidation product of phenidone (Also Dimezone S?) is of this type.So the question can be put if metol will regenerate this oxidation product and if the regeneration reaction depends on temperature.

  7. #17

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    Gerald, you right - velocity. but in same condition (pH, time, exp) as result of velocity we have density (I omit some mathematical background)

  8. #18

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    Quote Originally Posted by Relayer View Post
    Gerald, you right - velocity. but in same condition (pH, time, exp) as result of velocity we have density (I omit some mathematical background)
    It seems to me that there are at least three "flavors" in which the combination of developers could be measured: "velocity" or rate of reaching a certain density (or CI?), Dmax, and (D-fog)max, which I guess is basically CImax.

    My impression is that what's normally considered is velocity: how long does the combination of developers take to get the negatives to a "done" condition? To some extent that should correlate with CImax, because the longer it takes to "finish" your highlights, the more time the developer has to build fog. But it's not clear to me that the two should necessarily be interchangeable.

    Dmax by itself doesn't seem like a very useful measurement: you can develop to completion with any developer, I suppose, though you might get so much fog that the image is useless.

    I'm completely talking through my hat here, though, and I'm late for a meeting.

    -NT
    Nathan Tenny
    San Diego, CA, USA

    The lady of the house has to be a pretty swell sort of person to put up with the annoyance of a photographer.
    -The Little Technical Library, _Developing, Printing, And Enlarging_

  9. #19

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    I'm no chemist, but isn't there sometimes more to combining developing agents than superadditive behaviour?

    Also, while Phenidone is often described as a substitute for Metol, they don't work the same way in all respects, do they? For example, isn't Phenidone inherently more prone to streaking and uneven development than Metol? This can be a significant problem with POTA-type Phenidone developers, which I've observed myself. I remember reading (I think) about Glycin being combined with Phenidone in low contrast POTA-type developers mostly to improve uniformity.

  10. #20
    Ian Grant's Avatar
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    Never heard of Phenidone being more prone to streaking before.

    Ian

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