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  1. #1

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    Possible to replace Metol with Phenidone?

    I read somewhere that 10 g of Metol is equivalent to 1 g of Phenidone. If this is indeed the case, (1) would it be possible to use Phenidone rather than Metol in Barry Thornton's two-bath developer? (2) Is there an advantage to using Phernidone rather than Metol?

  2. #2
    David Lyga's Avatar
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    I did try Phenidone once and got fog. There is a way out of this but I state this to cause this factor to enter into the discussion. - David Lyga

  3. #3

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    Usually when replacing metol with phenidone other adjustments to the formula must be made. These can include changes to pH, restrainer, etc. So not a simple substitution.
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  4. #4

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    It is more complex than dividing 6.25 by 20.
    A better starter may be to start with an existing single bath Phenidone dev and split it into a two bath.
    Suggest desirable you wait for a real photo chemist to suggest a starting point.
    Failing that google POTA and use that in mean time.

  5. #5
    Rudeofus's Avatar
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    POTA is a very very low contrast developer and will most likely yield completely different results than regular one or two bath developers. Unlike with Metol, AFAIK there are no Phenidone only developers that would yield normal contrast. If you want a two bath developer with Phenidone, it will be Phenidone and a secondary developer, and I would suggest Diafine (using Phenidone and Hydroquinone, recipe here) as a starting point.
    Trying to be the best of whatever I am, even if what I am is no good.

  6. #6

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    As Gerald and Rudeofus have said, this type of substitution is more complex than a ratio.

    pH and other factors aside, I think there is often confusion regarding the replacement of Metol with smaller amounts of Phenidone. The context has to be kept in mind - ie when it is said Metol can be replaced with 1/20th-1/10th it's weight in Phenidone, this is in super-additive combinations (usually with HQ). As single developing agents Metol and Phenidone cannot easily be swapped. They are quite different.

  7. #7

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    Another problem is that when used alone Phenidone is unstable toward hydrolysis and oxidation. Another developing agent usually hydroquinone or ascorbate is required to stabilize it.
    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

  8. #8
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    A number of Phenidone-Hydroquinone formulae are known that work well.

    I substituted Metol. My home recipe was 645 first, which is 60 g sulphite, 4 g hydroquinone, and 0.5 g Phenidone to the litre. Donít forget the bromide.
    Some films allowed for half the amount of sulphite, so the recipe was 345. The thicker the film layers are and the more silver salts they contain, the more sulphite you use. Itís about balancing silver salt decomposition against early oxidation. 245 worked also.

    Agitate well. With continuous agitation you cut bath time by a quarter to a third.

  9. #9
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    The substitution is simple, although the ratio varies slightly) there's no need for pH adjustments however with print developers Phenidone gives warmer tones so if these aren't desired Benzotriazole is added alongside the Bromide.

    However as others have said Phenidone has low activity on it's own but had Super-additivity (becomes very active) alongside a second agent like Hydroquinone, Pyrocatechol, Glycin, etc.

    Ian

  10. #10

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    you can use phenidone instead of metol in this proportion:
    -- if the main developing agent is regenerated by another (hydroquinone);
    -- if the pH is under 9.

    In all other situations, the same subsitution is more difficult or impossible.

    Thornton's is a good divided developer using soft-working properties of metol to manage high-contrast situation. I don't know any divided developer using phenidone.

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