phenidone, benzotriazole and bromide

Discussion in 'Darkroom Developing and Printing' started by sreenath, Aug 12, 2004.

  1. sreenath

    sreenath Guest

    All,

    I have a question about potassium bromide in phenidone based
    developers.

    The formula for ID-68 is :
    Ilford ID-68 Buffered Borax Phenidone Fine Grain Developer

    Water, at 125°F 750.0 ml
    Sodium Sulfite, dessicated 85.0 grams
    Hydroquinone 5.0 grams
    Borax, granulated 7.0 grams
    Boric Acid, crystaline 2.0 grams
    Potassium Bromide 1.0 gram
    Phenidone 0.13 grams
    Water to make 1.0 liter

    Here, the mixture of borax and boric acid wll maintain a fairly low
    pH, low enough such that hydroquinone can't actualy develop film, but
    just regenarates phenidone.

    Then, this formula should contain benzotriazole to restrain phenidone.
    Instead we see Potassium bromide, which is supposed to be rather
    ineffective with phenidone, but highly effective with Hydroquinone!

    Can anyone throw some light on this?

    OTOH, ID-62, a paper developer, has both bromide and benzotriazole,
    which is understandable since with carbonate acting as the alkali,
    both phenidone and HQ need to be restrained.

    Thanks,
    Sreenath
     
    sreenath, Aug 12, 2004
    #1
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  2. I am not quite sure why but have asked an expert photo
    chemist about it and will post back if I get an answer. I
    can say that Phenidone is not insensitive to Bromide, just
    less sensitive than other developing agents. Hydroquinone,
    OTOH, is one of the most sensitive. The effectiveness of
    anti-foggants also depends on the pH of the solution. More
    later, I hope, stay tuned...
     
    Richard Knoppow, Aug 12, 2004
    #2
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  3. At this low ph, the bromide is effective.
     
    Michael Scarpitti, Aug 12, 2004
    #3
  4. sreenath

    Jorge Omar Guest

    As Richard has already posted, phenidone is sensitive to bromide
    (although less than to benzotriazole).
    Crawley, of FX devs fame, feels that bromide as a restrainer gives better
    acutance than benzo (see Anchel & Troop).
    Could this be the reason?

    Jorge

    (sreenath) wrote in
     
    Jorge Omar, Aug 12, 2004
    #4
  5. Regeneration is only one of several theories of synergism. Hydroquinone
    does develop at low pH, but has a long induction period. I prefer not to
    try to separate the functions of primary and secondary developers so
    neatly. As soon as development in hydroquinone begins, if there is sulfite
    in the solution, hydroquinone monosulfonate is formed. This is a more
    active developer than plain hydroquinone and is perhaps the reason
    hydroquinone has a reputation for high contrast. It starts slowly and
    accelerates. Anyway, bromide does have an effect on PQ developers. It is
    supposed to be at least partly responsible for edge effects, in that
    soluble bromide is formed from silver bromide during development and
    restrains development near areas of high density.
     
    PATRICK GAINER, Aug 12, 2004
    #5
  6. Some of his formulae use both.
     
    Michael Scarpitti, Aug 13, 2004
    #6
  7. sreenath

    friend® Guest

    if you believe that HQ monosulfonate is a stroner developing agent
    than hydroquinone, then consult scientific literature, compare
    half-wave potentials, rate of diffusion, kinetics etc.
     
    friend®, Aug 13, 2004
    #7
  8. I got that bit from "Theory of the Photographic Process" which is quite
    well known and is a compilation of articles by recognized authorities in
    the field.
     
    PATRICK GAINER, Aug 14, 2004
    #8
  9. Also, The MSDS for Kodak E6 first developer lists potassium hydroquinone
    monosulfonate as the only developing agent. This probably means that it also
    contains a phenidone derivative that is not in amounts sufficient to be
    considered worth mentioning, but if hydroquinone were as active or more
    active, it would surely have been used, since first developers are generally
    high contrast developers.
     
    PATRICK GAINER, Aug 14, 2004
    #9
  10. Logical, but not true. I once knew the published explanations for
    "infectious" development of Hydroquinone but have just not had an
    interest in the subject and can;t recall right now. What I do recall
    was that the creation of the monosulfonate was not it.

    The use of Potassium Hydroquinone Monosulfonate as the other
    ingredient in E6 First Developer was explained in a Kodak paper,
    excerpted in Dignan's Photo. Kodak used it in amounts approximating
    double that of Hydroquinone in order to obtain the same level of
    activity, as the Monosulfonate was "half used up". The benefit stated
    was that this "half used" state allowed the developers activity to be
    fine tuned and to be made more stable.

    Maybe.

    In any event, the Hydroquinone Monosulfonate was not regarded as more,
    but rather, less active than good old Hydroquinone.


    Robert Vervoordt, MFA
     
    Robert Vervoordt, Aug 14, 2004
    #10
  11. Even so, it has some activity that is not present when hydroquinone is used
    without sulfite. The monosulfonate cannot be formed in that case, and the
    activity is lower because, it appears, the synergism between phenidone or metol
    and hydroquinone is not activated. Furthermore, hydroquinone without sulfite is a
    staining developer related to catechol and pyrogallol. One theory has it that the
    monosulfonate is a product of the reduction of silver halide by the hydroquinone
    in the presence of sulfite.

    Whatever the theory, the fact is that phenidone is not used up until the
    hydroquinone is gone. Fully oxidized phenidone cannot be regenerated by
    hydroquinone. The amount of phenidone required to make a very active developer
    with either hydroquinone or ascorbic acid is so small that, by itself, it would
    take forever and a day to develop an image, but actually never would because it
    can't reduce that much silver. The activity of a developer containing 0.1
    grams/liter of phenidone increases with addition of hydroquinone until at least 8
    grams of hydroquinone have been added. Adding more causes very little increase of
    activity, but provides an increase in capacity.

    At any rate, the major developing agent in most PQ developers is the Q, and they
    are affected by bromide content. A pure phenidone developer is a different
    animal. Early research I saw reported showed that up to about 1 g/l of KBr the
    activity of a phenidone developer increased.
     
    PATRICK GAINER, Aug 15, 2004
    #11
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