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  1. #11

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    Quote Originally Posted by Photo Engineer View Post
    The two bases may be to adjust to the proper pH, but I see that the formulas above differ in pH with no explanation. In any event, use of 2 bases is not that unusual. I don't rule out chelation from TEA, just not as its primary function doe to its weak power as a chelating agent compared to its strong power as a base.

    Borate may offer some buffer capacity. Salicylic Acid is a weak chelating agent as well. It is claimed by some to offer protection to Ascorbates from oxidation by metal salts.
    Hmm, so the TEA and boric acid can form a buffer-system. I didn't know that. Now things are coming together for me. Thanks for the help!

    BTW, I wonder how effective the protection provided by TEA and salicylic acid really is. Ryuji himself noted that DS-10 stock only lasts two weeks.

    Here's an abstract of an article about salicylic acid working in conjunction with ascorbate in oxidizing/chelating iron:
    http://www.ncbi.nlm.nih.gov/pubmed/9575412
    I wonder if this is the article which motivated Ryuji to investigate salicylic acid...

    Mark Overton

  2. #12
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    There are several patents on this subject of Salicylic acid as an antioxidant (so to speak), but there are reported to be better compounds. Ryuji himself, here on APUG, stated that IIRC.

    As for a "buffer", well usually you use Carbonate and Bicarbonate as a buffer pair as an example, so my comment was only an analogy. Maybe a pH stabilizer or assisting agent would be better.

    PE

  3. #13

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    Quote Originally Posted by albada View Post
    .....Ryuji himself noted that DS-10 stock only lasts two weeks....

    Mark Overton
    That's not very long given that it has quite a few more ingredients than most developers. Xtol lasts a lot longer than that.

  4. #14

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    I am doubtful about the two week life for DS-10 and I wish that the poster had substantiated his claim. If this were true then what would be the point of using any chelating agent. RS stated that his print developer (also ascorbate based, and similar to DS-10) lasted for more than 6 months in his slot processor. I personally have used DS-10 for many weeks without problem and found that it works as well as Xtol. RS was seaching for a better chelating agent but was encountering problems with price and availability. But he was also reasonably satisfied with the salicylic acid/TEA combination.

    BTW, you can't use just any chelating agent in ascobate developers. Most agents actually increase the rate of oxidation. An example of a bad agent is EDTA.
    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

  5. #15
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    I suggest that those interested run some tray and bottle keeping tests then for both the print and film developers, and compare them with a references such as D-76 and Dektol.

    PE

  6. #16

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    Quote Originally Posted by john_s View Post
    That's not very long given that it has quite a few more ingredients than most developers. Xtol lasts a lot longer than that.
    Yes! So DS-10 will be used mostly mix-as-you-go, making preservatives unnecessary. So I'd like to simplify the formula. Also, I would use it stock (undiluted) with distilled water, so I probably won't need a buffer-pair in it to maintain pH.

    Here's an online pH-calculator I've been using: http://www.webqc.org/phsolver.php

    Let's start with the 8 grams of ascorbic acid and 75 grams of sulfite in DS-10. The calculator's inputs are pKa/b and concentration:

    Ascorbic pKa1=4.10 pKa2=11.6 c=0.045424
    Sulfite pKb=6.8 c=0.5950
    This gives a pH of 8.28. Let's add Ryuji's 1 gram of salicylic acid to help chelate iron:

    Ascorbic pKa1=4.10 pKa2=11.6 c=0.045424
    Sulfite pKb=6.8 c=0.5950
    Salicylic pKa=2.97 c=0.007240
    Now the pH is 8.21. Let's boost the salicylic acid to 5 grams:

    Ascorbic pKa1=4.10 pKa2=11.6 c=0.045424
    Sulfite pKb=6.8 c=0.5950
    Salicylic pKa=2.97 c=0.0362
    That drops the pH to 8.00, which is the target pH of DS-10. The corresponding formula is:
    .
    Water ................................... 750 ml
    Phenidone ............................. 0.15 g
    Ascorbic Acid ........................ 8 g
    Salicylic Acid ........................ 5 g
    Sodium Sulfite (anhydrous) .... 75 g
    Water to make ...................... 1 L
    .
    Well, that removes the TEA and the (hard to dissolve) boric acid, which I'm hoping were just a buffer-pair.
    Anyone want to take a guess how well this will work?
    I've ordered the additional chems from PhotoFormulary.com, so I'll soon be experimenting with this...

    Mark Overton

  7. #17

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    Quote Originally Posted by Gerald C Koch View Post
    I am doubtful about the two week life for DS-10 and I wish that the poster had substantiated his claim. If this were true then what would be the point of using any chelating agent.
    Ryuji said in a pure-silver posting, "At this point I do not recommend to store DS-10 for any more than a couple of weeks." Farther down in that posting, Ryuji says, "At this point, I mix DS-10 as I use."

    Here's the link: http://www.freelists.org/post/pure-s...-information,1

    So yes, it makes one question the addition of chemicals for preservation.

    Mark Overton

  8. #18
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    Mark;

    I hope you have a good pH meter. Also, note that the two formulas above have 2 different pH aims.

    You are in a very iffy position in that developer.

    Best luck anyhow.

    PE

  9. #19

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    Solubility of Salicylic acid in water is given here as ~2g/L
    http://en.wikipedia.org/wiki/Salicylic_acid

  10. #20

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    Quote Originally Posted by Alan Johnson View Post
    Solubility of Salicylic acid in water is given here as ~2g/L
    http://en.wikipedia.org/wiki/Salicylic_acid
    Yikes! Thanks for catching that mistake! 5 g/L of salicylic acid obviously ain't gonna happen.

    Quote Originally Posted by PE View Post
    You are in a very iffy position in that developer.
    I like removing ingredients while only half-knowing what I'm doing.
    Is the weakness the reliance on sulfite as the sole alkali? Or losing some chelation provided by TEA? Or altering the conversion of ascorbic acid into ascorbate?
    Or all of the above? /2

    Mark Overton

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