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  1. #11

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    Quote Originally Posted by gainer
    As Sandy said, if you can't use it before it spoils, mix it in propylene glycol instead of water. All you need is the phenidone and the catechol. The bisulphite is for preservation. Glycol does that. If you think you need sulphite for some other reason, add a little to the working solution or to the B solution. Don't use very much, or you will lose the stain. Phenidone and catechol with sulphite and alkali is not much different from an ordinary PQ developer. The working solution should have no more than about 1 gram for every gram of catechol. That much will assure the superaditivity of the catechol with the Phenidone.

    I find I can get good stain and tanning as well as good film speed without any sulphite.

    Thanks to the results of Pat Gainer's research I have been mixing my Pyrocat-HD Stock A solution in propylene glycol for several months, with excellent results. Here is what I do for mixing one liter of Stock A.

    1. Measure out the necessary amount of pyrocatechin, phenidone, bromide and potassium metabisulfite that goes into the Stock A solution. For one liter of Stock Solution A that is 10g of potassium metabisulfite, 50g of pyrocatechin, 2g of phenidone and 2g of potassium bromide.

    2. Heat about 950ml of propylene glycol in a Pyrex container to 250-275 degrees F.

    3. Add the pyrocatechin and stir until it is completely dissovlved.

    4. Add the potassium metabisulfite and stir until completely dissolved.

    5. Add the potassium bromide and stir until completely dissolved.

    6. Check the temperature of the solution and make sure it is below about 150 degrees F. If it is not continue to stir the solution, checking the temperature from time to time until it falls to around 150 F.

    7. When the solution is at 150 degrees F or slightly lower add the phenidone and stir until completely dissolved.

    8. Top off to make a total of 1000 ml of Stock A.

    Be very careful when working with solutions at 250 degrees F and higher. Even a drop of a solution that hot anywhere on your body is capable of inflicting severe damage.

    I have tested solutions prepared this way against a comparison Stock A Solution mixed with water and the results were virtually identical with the film tested.

    So far I have not tested the A solution in propylene glycol leaving out the bromide and potassium metabisulfite, as Pat suggests, but plan to do so soon.

    Sandy

  2. #12

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    ...So far I have not tested the A solution in propylene glycol leaving out the bromide and potassium metabisulfite, as Pat suggests, but plan to do so soon.

    Sandy[/QUOTE]

    I currently mix the A solution in propylene glycol using only the phenidone and pyrocatechol. For mixing, I use a hotplate/magnetic stirrer combination with a calibrated digital thermometer immersed in the solution. The phenidone and pyrocatechol both dissolve completely between 140 F and 160 F. The potassium metabisulfite and KBr can be added to the B solution. I have tested this version of Pyrocat-HD against the original formulation and have seen no differences.
    Tom Hoskinson
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    Everything is analog - even digital :D

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