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  1. #141

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    Do you have a temp sensor to correct your pH measurements?

  2. #142

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    Also, buffers, for whatever reason, often are off a little bit from calculated values. You can made fine adjustments to them. For borate buffers, use boric acid to make it more acidic, and sodium hydroxide to raise the pH.

  3. #143

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    Quote Originally Posted by Kirk Keyes View Post
    Home made pH meter? Sounds pretty good for home made.
    I'm using the electrode from a cheap Hanna pH-meter that broke, and a Fluke voltmeter shows the mV output, from which pH can be easily calculated using stored calibration-values. But I had to build a unity-gain box to buffer the weak output of the electrode. Pictures of it are about halfway down this page: http://www.apug.org/forums/forum37/1...ph-meters.html

    Mark Overton

  4. #144

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    I measure temperature with a thermometer and compensate manually. Commercial buffers have tables of pH-values based on temperature printed on them, so I know what pH to expect from them.

    Quote Originally Posted by Kirk Keyes View Post
    Also, buffers, for whatever reason, often are off a little bit from calculated values. You can made fine adjustments to them. For borate buffers, use boric acid to make it more acidic, and sodium hydroxide to raise the pH.
    That's good to know. Although if I can hit +/-0.03, that should be good enough. Do you think commercial buffers are that accurate? Anyway, my problem is that my home-mixed buffer was over 0.20 off from what I calculated, so I clearly made a mistake in the theory somewhere.

    Mark Overton

  5. #145

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    Quote Originally Posted by Gerald C Koch View Post
    I have never heard anyone other than yourself say that Phenidone produces more fog than Dimezone-S.
    I finally collected some test-strips I'd developed over the last few weeks, and measured base+fog (B+F) levels for Phenidone at various pH-levels using TMY2. All test-strips were developed to approximately the same contrast as XTOL. Here's the graph:

    Click image for larger version. 

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    The graph is jumpy and crude, partly because I changed pH-meters partway through. But it shows a trend: As pH rises, Phenidone's B+F rises. For comparison, XTOL uses Dimezone-S, and its B+F is .25 at pH 8.3 (with TMY2). Phenidone only gets close to XTOL's level when pH is no more than around 8.10.

    Caveat: All of the Phenidone developers in that graph use ascorbic acid and sodium metaborate. Other chemistries might cause Phenidone to behave differently.

    Mark Overton

  6. #146
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    Mark;

    Another good reason to use Dimezone-S, unless there is an antifoggant in XTOL!

    PE

  7. #147

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    Quote Originally Posted by Photo Engineer View Post
    Mark;
    Another good reason to use Dimezone-S, unless there is an antifoggant in XTOL!
    PE
    If only the crystallization issue could be solved. A concentrate with a little TEA and mostly PG crystallized. I'm thinking of reversing that by using mostly TEA and minimal PG to thin it some. A little citric acid will bring the pH back down. With so little PG in it, perhaps it won't crystallize.

    BTW, I forgot to mention that Phenidone gets slightly grainier as its fog-level rises. The difference is small enough that most people might not notice, but it's perceivable on close exam. That makes it more of a challenge for Phenidone to match the image-quality of Dimezone-S.

    Mark Overton

  8. #148
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    Coarse grains are less developable. As fog increases, the coarse grains are developed and thus the grain increases. This is a "normal" trait of fog formation.

    PE

  9. #149

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    A question for chemists and those who create developers:
    Why did Ryuji Suzuki and others use Salicylic acid and TEA to chelate iron, when DTPA will work?

    Here's some interesting info about DTPA: www.dow.com/scripts/litorder.asp?filepath=/113-01343.pdf
    Notice that Fe (iron) is included in the list of metals chelated. Iron is the curse of ascorbate developers because it eventually destroys all ascorbate via the Fenton reaction. Hence the motive to chelate iron. DTPA is used in XTOL (1 g/L, according to the patent), so I'm wondering why others don't use it.

    Mark Overton

  10. #150

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    For the very practical reason that both salicylic acid and TEA are easier to obtain than DTPA. I bought salicylic acid from my local compounding pharmacy.
    Last edited by Gerald C Koch; 09-01-2012 at 10:31 AM. Click to view previous post history.
    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



 

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