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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. #241
    gainer's Avatar
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    Quote Originally Posted by Ray Rogers View Post
    grain-sniffers ?

    That is what we old timers call viewers who get close enough to the photo to smell the grain and too close to see the picture.
    Gadget Gainer

  3. #242
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    You guys can keep looking for the perfect Rodinal (if that's what anyone is actually doing). I have found it. I tested it last night and left the used developer in an open 500 ml pitcher. I saw that the color had not changed appreciably, so I tested it again. The negatives are identical. The batch that I mixed a week ago has not changed color. It may be that the 2 week seasoning period imposed by AGFA was to give it a chance to get a little color.

    I follow the developing instructions on my old AGFA Rodinal bottle, not glass but the white plastic kind. The only change I make is to agitate on the minute instead of the half minute. There is something about European scenery or at least European photographers that drives them on average to a slightly higher contrast than I like.

    I used mostly the recipe proposed by Ian, but left bromide and the other stuff out for now. I don't miss it so far. I used somewhat less K2SO3, but still more than most other recipes dictate.
    To make 500 ml:
    Take 225 ml of the 45% K3SO3 solution and add to it 21 grams of paraminophenol base. This, of course forms a slurry that is protected by the sulfite from immediate oxidation by the KOH you are about to add. It will take at least 11 grams of KOH to dissolve the precipitate. I do not know how to tell you to keep KOH, even dry, from forming K2CO3 with atmospheric CO2.

    Gotta go now. Talk later.
    Gadget Gainer

  4. #243

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    Just a few random comments:

    First, I have only skimmed through about half the comments on this thread, but I want to congratulate PE and Patrick for keeping a civil tone so far!!! Thank you both.

    Next, a few comments and questions about hydroxide chemistry. First, a well-know quirk about hydroxide is the ability to absorb atmospheric CO2 and be converted to carbonate. This would obviously change the pH of the hydroxide solution. Are there special considerations that photographic chemists take to minimize this effect? I suppose that keeping bottles capped would go a long way toward controlling this.

    Second, hydroxide solutions are known to attack glass, converting the silica in the glass to silicate. This could have two effects. The first is to damage glass bottles. The second is, as with the CO2 chemistry noted above, a shift in pH of the solution. In fact, the chemistry of the conversion of SiO2 to SiO3-- is very analogous to the conversion of CO2 to CO3--, given the relative positions of C and Si in the periodic table. Is the silica-silicate chemistry noted here something of concern in photographic chemistry?

  5. #244

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    Oops, what do you know, Patrick's post just ahead of mine (and possibly some others as well) mentioned the hydroxide, CO2, carbonate issue. I hadn't gotten that far in the threads when I made my post, so I apologize if my post seems out of sequence or deals with something already covered.

  6. #245
    Photo Engineer's Avatar
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    Alan;

    I mentioned somewhere the reaction of glass with hydroxide. In fact, my 50% hydroxide solution is starting to etch the glass dropper bottle that it is in. I use a dropper for addition of the last bit of hydroxide. (well, at least I did! )

    It takes a fair amount of time to etch even the cheaper glass in the dropper bottles and it goes after the clear glass dropper first.

    PE

  7. #246
    Ian Grant's Avatar
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    Following on from Ron's (PE) comment. Early Rodinal and modern Calbe R09 has no free Hydroxide anyway so is not going to etch glass. Even modern Agfa/A&O Rodinal only has a small amount of free Hydroxide so even when it was still supplied in a glass bottle it would have taken a considerable number of years longer etch the glass than a 50% solution

    Ian

  8. #247
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    Ian;

    If the pH is above 7, there is free hydroxide. As the pH increases, the amount of OH increases. So, by the reports that the pH of the stock is about 11 or 12, this is pretty strong stuff.

    PE

  9. #248

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    Quote Originally Posted by gainer View Post
    I do not know how to tell you to keep KOH, even dry, from forming K2CO3 with atmospheric CO2.
    You can apply tape (electrical tape works well) around the lid of the bottle to help the lid seal better. You may have noticed that many chemicals come packaged that way. It not only keeps the air/moisture/CO2 from getting into the bottle, it also helps keep the contents of the bottle in the bottle.
    Kirk

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

  10. #249
    Ian Grant's Avatar
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    Quote Originally Posted by Photo Engineer View Post
    Ian;
    If the pH is above 7, there is free hydroxide. As the pH increases, the amount of OH increases. So, by the reports that the pH of the stock is about 11 or 12, this is pretty strong stuff.
    PE
    Strong as in a 50% soloution of Potassium Htdroxide, quite the opposite

    My Jacobson & Jacobson lists Potassium Hydroxide at 0.05% as giving a pH of 12, 0.5% a ph of 13, and then the Potassium Sulphite level on it's own would give a pH of 9-10.

    Calbe R09 with no free Hydroxide does indeed have a pH of 11.8, all version of the formulae until Agfa's 1964 re-formulation contained no excess hydroxide - just enough to react with the free base. If this wasn't the case the pH would be higher we know that the amount of KOH needed to reactwith 50g of Free base is 24g. At 2.4% that should give a pH of somewhere around 13.5, but it doesn't - that's they key to what's going on with Rodinal.

    Now take into account that modern Agfa/A&O Rodinal has a pH of nearer 14 but has 20% less (approx) p-Aminophenol it also contains more Potassium Hydroxide 2.7% that when it reacts with the Free Base leave 0.73% free hydroxide which gives a pH of over 13 exactly as we'd expect.

    This hold the key to Rodinal, it starts life as the p-Aminophenol free base then there's a reaction with the Hydroxide, which may be slow.

    If the hydroxide doesn't react then the Calbe R09 would have a pH close to the Agfa/A&O version - which it doesn't.

    Ian

  11. #250
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    Ian;

    I have to disagree. If the pH is above 7, then the OH concentration goes up one order of magnitude for every pH unit from 8 - 14. It is as simple as that. So, at pH 11 or 12, there is excess free OH present. There is no question. This is basic chemistry!

    PE



 

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