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  1. #1

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    Interesting. For another possible way to preserve the ascorbate, see Kodak's patent on liquid ascorbate developers:

    http://www.apug.org/forums/showthrea...t=kodak+patent

    Basically, they mix in a lot of glycol in the stock solution.

  2. #2
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    Please take note of the fact that ethylene glycol is very toxic. Propylene glycol is replacing it wherever possible in many applications.

    Ethylene glycol is particularly insidious due to its pleasant sweet taste. Be carful of it and solutions containing it around children and pets.

    PE

  3. #3

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    Gainer's PC-Glycol uses propylene glycol (or potentially other glycols), but it's highly concentrated; I use it 1:1:48 (it's a split-stock developer). Propylene glycol would certainly be expensive for anything that's used one shot without dilution, but if it's diluted for use or if it's in a re-usable stock solution, it could be reasonable from a cost perspective. PC-Glycol puts ascorbic acid and phenidone in the glycol, and Gainer's published articles with "torture tests" involving leaving a shallow pool of this out for about two weeks with no loss of activity. I don't know enough about the chemistry to say how ascorbic acid and sodium carbonate in glycol would work, or even if sodium carbonate is soluble in glycol.

    There's another issue with glycol, though: It's more viscous than water, although not nearly as viscous as, say, TEA. I'm not sure how much of a problem that would be for a developing solution.

  4. #4

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    Although bits of the ideas are interesting, I have fundamental question regarding the advantages of two bath development. I don't see much benefit that can only be obtained by two bath method. You described the images obtained in very subjective terms but you should at least compare against D-76 or some other standard developers.

    The relation between developer activity and pH is not fixed. Some agent like hydroquinone is very pH dependent, and Metol less. Amidol has even less pH dependency. The difference is that the hydroxyl groups and amino groups in developer molecules have different patterns of dissociation, and for hydroxyl groups, the deprotonated form is active, and this is where the pH dependency comes in. What is really important is not the pH alone, but the developer species distribution at the operating pH. For this reason, there is no advantage to use amidol at a low pH for two bath developers. (And in general, there is nothing special about amidol just because it works at neutral or acidic pH.)

    The research in 1930s tried many of your ideas for two bath development. They even tried two bath development where A and B are identical general purpose developer. Before making duplicate effort, you should spend time to learn what's already figured out. They also tried different agents in A and B bath.

    When you use one agent in each bath, the superadditivity may be seen to a verying degree. The superadditivity depends on the fact (among other factors) that the radical form of the electron transfer agent (ETA) is rather stable. Generally speaking, the more stable the ETA radical is, the more superadditive effect the combination will have. In the two bath approach with ETA in A bath and main developer in B bath, the ETA radical's life may not be long enough. Also, agent like metol is easily sulfonated in presence of sulfite and may get lost before superadditive effect kicks in. This only complicates the situation and makes it difficult to verify robust operation of the developer in a range of conditions. In other words, too much risk for no or little meat.

    It is very alarming that my results are quoted out of context. I did not say a solution containing ascorbic acid and salicylic acid will keep for a long time even at low pH. The effect of salicylic acid is pH dependent, like many other things. Also, note that I don't rely on sal alone in DS-10, 12, 14, etc. Another thing is that I may have said "ascorbate solution is easy to formulate to keep longer at a higher pH than at a lower pH, when transition metal impurities are present" in several different ways, but I did not mean that ascorbate-carbonate solution would keep for a very long time. For example, if there were absolutely no impurity, I bet the solution would keep longer at a lower pH. I know this may be a bit complicated, but it only shows that how little is understood about this problem. Generalization is possible only after the science part is largely worked out, and we aren't there yet.

  5. #5

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    Jdef, if you want one session developer, replenishment method works well. Replenishing by bleed method is pretty easy and reliable, and while it is not the most economical method, it is a lot more economical than one-shot approach. You can use most general purpose developer. Use seasoned solution as the starter developer and use unseasoned but otherwise identical solution for the replenisher. Depending on the formula, you might want to tweak the replenisher formula a bit, but if you do bleed method, it is nowhere near as sensitive as top up method.

  6. #6
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    Jay:

    Another thought. Rather than trying to make the B solution last longer, if we accept that it's a short lived solution, then perhaps not ruling out Amidol in the A solution should be looked at? I've found that the Michael A Smith Amidol formula can last a few days if it's kept in a full container, so Amidol might work well for what you want to do.

    -Mike

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    I made up 2 liters of Amidol stock concentrate a year ago - it is still fully active today. I simply dissolved the dry Amidol in Propylene Glycol. I use the Amidol concentrate when I mix Michael Smith's Azo developer formula. That way, I only need to handle the dry powder once (under a hood).
    Tom Hoskinson
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  8. #8
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    Quote Originally Posted by Tom Hoskinson
    I made up 2 liters of Amidol stock concentrate a year ago - it is still fully active today.
    Tom:

    What quantity of Amidol did you mix in the 2 liters of PG? I've also mixed Amidol in PG, and it does last a long time that way. I've mixed a 1% solution which I use for adding to PMK, as well as some more concentrated that I used to make the MAS print developer (it was a while ago, and I don't remember what strength I mixed it!)

    -Mike

  9. #9
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    If you find what you think you are looking for in a 2-bath developer, be sure you compare its results with what you get by mixing the parts together and doing it all at once. I became enamored of D-23 with a borax B bath about 40 years ago, thinking what wonderful gradations, speed, you name it. Then I did a critical comparison and found that D-23 did the same thing all by itself. The only reason I can think for using 2 baths instead of 1 is, theoretically, the developer never dies, it just goes away, and there is also the claim of no worries about time and temperature.
    Gadget Gainer

  10. #10

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    Quote Originally Posted by MikeS
    Tom:

    What quantity of Amidol did you mix in the 2 liters of PG? I've also mixed Amidol in PG, and it does last a long time that way. I've mixed a 1% solution which I use for adding to PMK, as well as some more concentrated that I used to make the MAS print developer (it was a while ago, and I don't remember what strength I mixed it!)

    -Mike
    Mike: I used 18 grams of Amidol per liter of glycol. Using the concentrate, I have found that I got excellent working developer performance with 6 grams of Amidol per liter of the working developer.

    By the way, there is always a small amount of insoluble Amidol debris in the glycol concentrate. Adding more glycol doesn't help. However, the debris dissolves readily in water.
    Tom Hoskinson
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