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  1. #1
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    Why Pyrol rather than hydroquinone?

    Just started into the mixing up my own staining developers. I found a lots of formula dealing with pyrol and catechol but almost nothing with hydroquinone. Did some research on the great wide net but not much in the way of hits (maybe looking in the wrong places) for a staining developer based on hydroquinone. I am not wanting to rehash the old news of staining versus regular developers, but why most formulas have chosen to use pyrol or catechol rather than hydroquinone. Is there a major advantage with grain, accutance, and tone with pyrol or catechol over hydroquinone? I just mixed up a hydroquinone developer (formula from another thread here), so not committed 100% yet to it and just doing more research before ordering more chemicals to play with.

    Elvis

  2. #2

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    I think the reason is that hq won't stain if there's more than a minute amount of sulfite in the developer, and sulfite is the traditional preservative of choice. There are ways of getting around this, of course. As Gainer has shown, you can use an organic solvent instead of water for the stock solution. The other way is to mix the developer from powder right before use. I did this with good results. Hq dissolves quickly in water.

  3. #3
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    Sounds interesting. I don't recall sulfite as I have it as a two parter and I mixed it up a couple of weeks ago. Developed with it just a couple of times so far. Count is 5 good sheets, to one badly streaked one.

  4. #4

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    Is this the one modified from Pyrocat by Mehment Kismet? It contains a small amount of bisulfite, which produces sulfite ions. The amount is so small that it won't prevent stain, but neither will it do much to preserve the stock solution, I think. I imagine the keeping qualities could be pretty good anyway.

  5. #5
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    I think that's the one. It looked like a good one to try since I had all the necessary chems on hand.

  6. #6

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    I'm tempted to try it myself. BTW, I neglected to mention that the reason it contains sulfite ions is that these are necessary to activate the hq-phenidone synergy. Without them, the developer would be a lot slower.

    Are you getting a lot of stain?

  7. #7
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    Its seems to be working well. Lots of brownish coloured staining. Only bad sheet I got had some nasty streaks of brown on it. Until now, the last few sheets looked fine. Using APX100 at EI=50 @ 8 minutes.

  8. #8

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    hydroquinone only has two phenolic sites on it vs 3. hydroquinone does not crosslink with the gelatine as readily as pyrogallol or pyrocatechol. Crosslinking is what chemically binds the pyrogallol to the gelatine causing stain.

  9. #9
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    Quote Originally Posted by avandesande
    hydroquinone only has two phenolic sites on it vs 3. hydroquinone does not crosslink with the gelatine as readily as pyrogallol or pyrocatechol. Crosslinking is what chemically binds the pyrogallol to the gelatine causing stain.
    So can I assume that it is due to this that the speed of development is slower that using pyro or catechol? I have lots of staining on my negs so the staining isn't an issue but I guess the development time and the amount HQ used maybe.

  10. #10

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    HQ does oxidize more slowly than pyrogallol/catechol so this would probably explain the slower speed. It also has a better shelf life for the same reason.

    Crosslinking is why pyrogallol is used to tan leather. It actually chemically binds the protein strands together which make them tougher and harder.

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