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  1. #61

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    I'm a little surprised to see that you guys are getting development from M-C mixtures without sulfite. I've used MC-TEA for quite a while - wonderfully sharp and fine-grained results on Delta 400 - but it doesn't do a thing without some sulfite added to the water - I use two teaspoons, or about 10 g/l. I guess it could be an issue of alkalinity.

  2. #62

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    Superadditivity

    I have used PC-TEA and there is no problem getting adequate development without sulfite. I think I used a slightly incorrect amount of ascorbic acid so my times for FP4+ at 1:50 at 68 degrees F were 13 minutes or longer. Whether some combinations give actual superadditivity or just seem that way is an academic question. Once you have the time/temperature/EI figures worked out, you are in business. I have read that hydroquinone has either very little activity or no activity below a certain temperature. That temperature might be about 60 degrees F. When the hydroquinone does get active I don't know whether its activity increases in a liner or non-linear way as temperature increases.

    Even if digital photography had not advanced as quickly as it did, there would still have been pressure to reduce the toxicity of the chemicals used. Color processing was mostly done on a larger scale and for many years the spent chemicals were picked up and treated in some way rather than just being dumped somewhere in an unsafe way. There isn't that much large scale traditional b&w processing being done now. This makes it even more important for small scale users to learn how to handle the chemistry safely. I think there were three factors in the interest in phenidone over metol in recent years. The first was that phenidone is less toxic than metol. Secondly, even though successful developers combined phenidone with hydroquinone, ascorbic acid is far less toxic than hydroquinone. If you use PC-TEA you even eliminate the sulfite and the amount of TEA used in a 1:50 dilution is quite low. Finally, the newer technology films and the improved old technology films (like Tri-X) respond better to phenidone than the older films did. The increase in grain is not very apparent and the improvement in sharpness is welcome.

    You can do a lot with PC-TEA and do it more safely than with Rodinal or pyro type developers. I think that if developing times were too long or if we were using large rubber tanks with replenishment then superadditivity would be more relevant in practical terms. I any case this thread has been interesting to read.

  3. #63
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    I have gone a little farther since last time. The combination of Metol and ascorbic acid gives the same activity as Metol and sulfite if the pH is 8.7, according to Mees & James. You can get close to that by a simple combination of 8.5 grams Metol, 8.8 grams ascorbic acid, 4 grams of sodium hydroxide and 10 grams of borax in water to make a liter. You can replace both hydroxide and borax with 28 grams of sodium metaborate (Kodalk will do). This combination should be very active. You will probably want to dilute it 1:1.
    The ascorbic acid could be replaced by sodium ascorbate, in which case cut the hydroxide in half. However much borax you put in will not give pH much higher than 9.2. As little as 4 grams will give pH about 9.2. Sodium ascorbate is close to neutral. Have fun.
    Gadget Gainer

  4. #64
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    I should have mentioned that the hydroxide is sufficient to neutralize the sulfuric acid attached to the Metol and to convert the ascorbic acid to sodium ascorbate which is only slightly basic. The solution wouldn't do much developing without the borax.

    We often substitute 14.5 grams sodium hydroxide plus 69 grams of borax in a liter of solution as 10% sodium metaborate. 276 ml of such a solution contains 4 grams of the hydroxide and about 20 grams of borax, whether you mixed it that way or from 27.6 grams of sodium metaborate. I have tested both ways.
    Gadget Gainer

  5. #65
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    I should also have said that this solution is not awfully much different from D-23 in activity.
    Gadget Gainer

  6. #66
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    METOL-ASCORBATE

    Quote Originally Posted by gainer View Post
    I should also have said that this solution is not awfully much different from D-23 in activity.
    I DON'T KNOW WHAT I'M INTO HERE, BUT HERE GOES.
    Gadget Gainer

  7. #67
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    Metol-ascorbate

    This is my third try to get the attachments attached.
    Attached Thumbnails Attached Thumbnails FP4MCB10X.jpg   FP4MCBDET.jpg  
    Gadget Gainer

  8. #68
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    These attachments really belong with the article and chem recipe about Metol and ascorbic acid.
    Gadget Gainer

  9. #69
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    Quote Originally Posted by gainer View Post
    I should also have said that this solution is not awfully much different from D-23 in activity.
    Pat,

    Do you have any idea what shelf life of the stock solution might be?

    Thanks

    Mike Sullivan

  10. #70
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    I haven't had it long enough to know, but I expect it to be quite long. If it is true that the role of the ascorbate at this pH is to replenish the Metol and not superadditivity, the ratio of remaining ascorbate to Metol will not be important. The pH and bromide content of used or aerated developer is more important. There wont be any bromide build up due to aeration, and most will use it one-shot so bromide won't be a problem. The rather generous quantity of borax wont allow much change in pH during one shot use. I'm planning to leave a pint or so in an open container to see if it's still good after a month or so.
    Gadget Gainer

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