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  1. #1
    Ian Grant's Avatar
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    Modern Rodinal Substitutes Part II

    Apologies for having to start a new thread but I can't read or even access the first to reply to posts.

    So with a bit of telepathy

    Quote Originally Posted by Kirk Keyes View Post
    Well, there's a problem there, as it's really hard to measure pH accurately when it gets much above 12.5 or so. You have to start getting special electrodes and the like.

    But for MSDS work, it doesn't have to be too precise.
    __________________
    Kirk

    A point that's being missed is that A&O give a figure of 2.7% Potassium Hydroxide not 3% in older Agfa MSDS.

    The pH is around 14 sure, but the actual requirement is the pH of the working dilute solution rather than the concentrate which is given elsewhere as pH 11.55, which I commented on in the first post of the thread.

    Way back Ron (PE) mentioned adjustments to Rodinal before bottling, the question we need to ask is are they adjusting on the basis of the concentrate, or also doing some tests on a dilute sample, as this will be a far more accurate indicator.

    Can someone please post a link to this continuation on the original post.

    Ian

  2. #201
    gainer's Avatar
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    Quote Originally Posted by Alan Johnson View Post
    Vit C formulas may contain undissociated metol carbonate if there is such a thing,IDK.
    Ascorbate probably does not form undissociated compound with metol which would be present as its aminophenolate.
    The apparent superadditivity between Metol and ascorbic acid seems to be due to the ascorbate's ability to regenerate Metol. It is acting more as an antioxidant if that is true than as a developing agent. This is not my theory. I happened across it in Mees & James "The Theory of the Photographic Process" , fifth edition, third printing, 1969. I didn't see any speculation in that reference about the aminophenolate being formed in those experiments.
    Gadget Gainer

  3. #202

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    I dont think there has been much discussion of the form in which developing agents exist in solution.
    Metol is methyl p-aminophenol sulfate.In sodium hydroxide(Metolal) it may form sodium methyl p-aminophenolate.In Rodinal is potassium aminophenolate.Metolal and Rodinal are chemically similar,may have similar tonality.
    In Vit-C developers with carbonate it may be the metol exists in solution partly as a different compound,not sodium methyl p-aminophenolate.They are less likely to be Rodinal-like.
    In sodium hydroxide+sodium ascorbate its anybodys guess in what form the metol exists,but it favours my case that it should be aminophenolate so I'll stick with that.

  4. #203
    gainer's Avatar
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    Quote Originally Posted by Alan Johnson View Post
    I dont think there has been much discussion of the form in which developing agents exist in solution.
    Metol is methyl p-aminophenol sulfate.In sodium hydroxide(Metolal) it may form sodium methyl p-aminophenolate.In Rodinal is potassium aminophenolate.Metolal and Rodinal are chemically similar,may have similar tonality.
    In Vit-C developers with carbonate it may be the metol exists in solution partly as a different compound,not sodium methyl p-aminophenolate.They are less likely to be Rodinal-like.
    In sodium hydroxide+sodium ascorbate its anybodys guess in what form the metol exists,but it favours my case that it should be aminophenolate so I'll stick with that.
    I did part of that last thing once. I compared hydroquinone-sulfite-hydroxide-bromide with ascorbic acid-sulfite-hydroxide-bromide for graphic arts. The results were quite similar. Don't remember much about it, but used it once to do a simulated line drawing of conductor Russell Stanger for the Norfolk Symphony's program booklet from a photo I took of him. There was no Metol, but it shows the developing power of ascorbate as sole agent when pH is high enough. Both needed great gobs of bromide to keep fog away.
    Gadget Gainer

  5. #204

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    Guys - for determining what happens to what in solution, maybe you'd like to review the following terms:
    Ampholyte
    Zwitterion
    Isoelectric point
    pKa
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  6. #205
    gainer's Avatar
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    You mean for predicting what happens. Sooner or later, you have to try it, why not sooner? There are times when one learns more by trying something and then searching for the reason it didn't work. I learned more about integration by parts by trying to use a published equation that had an error. It turned out to be a typo, but I had to go through the pertinent aerodynamic equations to find that it was a misplaced absolute value sign.
    Gadget Gainer

  7. #206

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    I mean for both predicting and understanding why it happens.

    When something that doesn't dissolve when it is believed that it should, well, maybe there's something missing in that original belief...

    And using good sources is important, too, as you pointed out.
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  8. #207
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    I don't know how we got on this path. Once upon about 30 years ago, I was first chair oboist and "principal photographer" for the Norfolk symphony. It was in the musician's union contract, would you believe? I had a good shot of the conductor that the board wanted to posterize and use on posters. I had a recipe for the necessary developer but no hydroquinone, so I tried ascorbic acid and it worked, but not without expectations. I had access to a lot of books on every conceivable subject and I did know how to read. My Daddy taught me at the age of 5.
    Gadget Gainer

  9. #208
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    I am working on a set of experiments that may lead somewhere on the Rodinal trail. I made a solution of p-aminophenol base in glycerine such that 10 ml of it would contain the amount of p-aminophenol that is probably in 1+50 Rodinal working solution. Exactness is not critical at this stage. Adding enough KOH to make the pH over 12 makes it as black as a coal mine at midnight with the hatches down, but develops HP5+ in 16 minutes at 70 F, which is about what the Germans would put on their chart if they believed in CI < 0.65. Next, I made the same solution but added the 7.9 grams of K2SO3 that one would get in the working solution by adding 384 grams per liter of stock, again making pH over 12. 9 minutes now gets normal contrast. I don't know how much enlargement it would take to make a significant difference in grain or gradation. 30X hasn't done it for me.

    Back to the dungeon.

    I still need a comparison to something like D-76.
    Gadget Gainer

  10. #209

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    Quote Originally Posted by Kirk Keyes View Post
    I mean for both predicting and understanding why it happens.

    When something that doesn't dissolve when it is believed that it should, well, maybe there's something missing in that original belief...
    Kirk,

    Is there anything you know about these (Ampholyte, Zwitterion, Isoelectric point) that specifically relates to Metol, Rodinal, or Developers in general?

    That is, can you give some real world examples so we can learn something?
    (I agree with the concept... but I don't have the skills just now to apply them to developers) can you show us what you mean with a practical example?

    Thanks,

    Ray

  11. #210
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    Ray;

    With a simple google, you find: http://en.wikipedia.org/wiki/Zwitterion

    You cana do the same with the others. However, I explained and posted a graph regarding Isoelectric Point with regard to gelatins some time back.

    PE



 

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