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  1. #1

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    About to mix PC-TEA, two questions left

    I'm about to mix some PC-TEA for the first time. The shop from which I bought the chemicals had TEA and ascorbic acid with the highest purity (> 99%), but Phenidone with 97%.
    Should I use the amount given in the formula, or use a little more (such as X/0.97)? I guess it's nothing to be worried about...

    My second concern is about how much Phenidone to use. The 3rd edition of the Darkroom Cookbok specifies 0.5g per 100ml Stock, most sources state 0.25g for the same volume. Does the larger amount just provide some safety for higher dilutions or does it significantly change the results in normal use (i.e. one-shot use, dilution 1+50 and two rolls of 135/36 per 500ml).

    Matthias

  2. #2

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    It's hard to weigh the small amount of phenidone with 97% accuracy and it probably has no detectable effect until the error is notably larger.
    I have always used the formula here:
    www.photosensitive.ca/wp/?s=gainer
    Some times are here:
    http://www.digitaltruth.com/devchart...TEA&mdc=Search
    or see under "unlisted data" ; for PC-TEA use Xtol 1+2 times ( I assume this refers to the 1:50 dilution).
    I expect these times would have been found using the 0.25g Phenidone version.
    It's hard to say what would happen if the Phenidone is doubled as in the Cookbook version.

  3. #3

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    Thanks, Alan! Yes, ist seems that the "0.25g forumla" ist by far the most used. Accourate weighing would not be the problem, since I got a very good scale from my uncle who worked as a chemist. But of course even the best scale will show inaccuracy to some degree, unless it's being calibrated regularly.

    I wonder what's the reason for the differing instructions in the Cookbook. They don't give a clue and it's unlikely to be a typo because i read somewhere that it was adopted to the newest edition from the last one.

    EDIT: Found two posts by gainer regarding the issue in this thread:
    Some of you will be surprised, I'm sure, that 10 times the amount of phenidone made no significant difference in the negatives. As long as you keep the ascorbic acid constant and the phenidone at least a fortieth of that amount, there will be neither advantage nor disadvantage to increasing the phenidone.
    and
    I did make the contact sheet comparing the two phenidone concentrations side by each, and the biggest difference I could make out was a slight increase in base fog with the increased phenidone. What else was in your developer?
    He was using 0.225g and 2.25g for this comparison, so it seems one can use 0.25g as well as 0.5g without hesitation. However, 0.225g (1/40th of the amount of ascorbic acid) should be the absolute minimum.
    Last edited by mcilroy; 03-22-2011 at 10:13 AM. Click to view previous post history.

  4. #4

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    I don't have a scale, so that's how I mixed it - with 1:40 ratio. For 1:50 dilution the times correspond with the Xtol 1:2. For 1:25, it's Xtol 1:1 times. I don't like long development times.

  5. #5

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    I mix mine with 0.25g of Phenidone per 100ml.

    I tend towards an average of Xtol 1+1 and Rodinal 1+50 times for developing in PC-TEA 1+50. If those times are very different, I'll also consult the D76 1+1 times.

    If in doubt, 9-10 minutes is a good starting point for 1+50.

    BTW, the concentrate has a very good shelf life, with no discernible change in activity after more than three years, even when the colour has changed from dark straw to rather dark.

  6. #6

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    Pat Gainer used a ratio of phenidone to ascorbic acid of 1:40. However many PA formulas use a higher ratio 1:60 or even 1:80. In later posts he mentioned using 0.225 g of phenidone for 10 g of ascorbic acid.
    Last edited by Gerald C Koch; 03-25-2011 at 11:30 PM. Click to view previous post history.
    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

  7. #7

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    Thanks all! I went with 0.3g Phenidone to be on the safe side (can't get it 99% pure) and the first developed roll of Acros looks very promising.
    Matthias

    Once you get born you're never the same.



 

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