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  1. #11

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    Quote Originally Posted by Tronds View Post
    The reason for using sodium carbonate is that you have to convert ascorbic acid to ascorbate. The pH required for this conversion is above the pH of borax.
    Here is a PC-type developer called PCB which only uses Borax as its alkali: http://www.apug.org/forums/archive/i...p/t-91805.html
    It consists of 19g borax + 6g ascorbic acid + 0.15g phenidone in 1L water.
    Therefore, Borax alone is sufficient, so carbonate is not needed.
    I suggest that you try omitting the carbonate from your formula, and adjust the pH another way, perhaps with Sodium metaborate or more Borax. It may work well, and maybe with less grain.

    But here's another question: You can increase the carbonate and then omit the borax, keeping the same pH. How would this affect image-quality? I guess that grain will be worse, but I'm not sure.

    Mark Overton

  2. #12

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    You can probably do away with or use less of the sodium carbonate as there's already enough borax to neutralize the ascorbic acid. To neutralize 10g of ascorbic acid (0.057 moles) you can use the following:

    borax = 10.83g
    sodium carbonate = 6.02g
    sodium bicarbonate = 4.77g
    sodium hydroxide = 2.27g

  3. #13
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    I am not aware of any great degree of synergy between phenidone and ascorbate. Certainly none like we have between Metol and HQ. As for the claims here, it seems more like hand waving or smoke and mirrors. For example, the statement that Carbonate is needed to convert Ascorbic Acid to Ascorbate, and then you add Borax is quite contradictory.

    Gerald has it right! You need to suppress Fenton oxidation (although we refer to it mainly as involving just Iron salts), which is what is effectively the real problem with Ascorbate developers.

    PE

  4. #14

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    Quote Originally Posted by albada View Post
    Here is a PC-type developer called PCB which only uses Borax as its alkali: http://www.apug.org/forums/archive/i...p/t-91805.html
    It consists of 19g borax + 6g ascorbic acid + 0.15g phenidone in 1L water.
    Therefore, Borax alone is sufficient, so carbonate is not needed.
    I suggest that you try omitting the carbonate from your formula, and adjust the pH another way, perhaps with Sodium metaborate or more Borax. It may work well, and maybe with less grain.

    But here's another question: You can increase the carbonate and then omit the borax, keeping the same pH. How would this affect image-quality? I guess that grain will be worse, but I'm not sure.

    Mark Overton
    Increase carbonate and omit borax to get the pH where borax is a perfect buffer? (9.1 -9.2)
    Why? at pH 9.1 to 9.2 I can add a lot of borax and the ph won't change. The acid products created during development will not change the pH when a lot of borax is used.
    Why shouls I increase carbonate then?
    The best is to get rid of the carbonate alltogether.
    The reason for having it there is to convert ascorbic acid to ascorbate in a way that ensures me that all of it is really converted. There is no other reason for having the carbonate there.
    I am not completely satisfied with the conversion of ascorbic acid to ascorbate in a pure borax solution. You will get ascorbate, but how much? How fast?
    Using carbonate works great for this purpose.
    The amount of carbonate doesn't affect the pH of the finished developer, so I don't use it to adjust pH.
    Please do some tests and you will discovder that this is true.

  5. #15

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    Quote Originally Posted by MichaelMadio View Post
    You can probably do away with or use less of the sodium carbonate as there's already enough borax to neutralize the ascorbic acid. To neutralize 10g of ascorbic acid (0.057 moles) you can use the following:

    borax = 10.83g
    sodium carbonate = 6.02g
    sodium bicarbonate = 4.77g
    sodium hydroxide = 2.27g
    You are probably right. I just want to make sure that I get ascorbate from the ascorbic acid.

    It doesn't matter when it comes to cost. Carbonate is dirt cheap.
    It doesn't matter when it comes to pH either since the large amount of borax controls the pH.

  6. #16

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    Why does this developer have long shelf-life?

  7. #17

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    Quote Originally Posted by Photo Engineer View Post
    I am not aware of any great degree of synergy between phenidone and ascorbate. Certainly none like we have between Metol and HQ. As for the claims here, it seems more like hand waving or smoke and mirrors. For example, the statement that Carbonate is needed to convert Ascorbic Acid to Ascorbate, and then you add Borax is quite contradictory.

    Gerald has it right! You need to suppress Fenton oxidation (although we refer to it mainly as involving just Iron salts), which is what is effectively the real problem with Ascorbate developers.

    PE
    You don't know that phenidone and ascorbate forms a superadditive pair?
    Yeah! You are a great photo engineer. NOT!

    Besides that, the TCB-developer we are discussing here doesn't have any phenidone.
    You talk about Fenton. What is that? A friend? A foe?
    Can you please stick to discussing what this developer does and what it contains.
    All your talk about Fenton seems more like hand waving or smoke and mirrors.

    Oxydation of Fenton (whatever or whoever that is) isn't the problem with ascorbate developers. The problem with ascorbate developers is oxydation of the ascorbate. When the ascorbate has oxydated, it can't protect other developing agents anymore, and since it doesn't woirk as intended anymore, the activity of the developer goes down.

    If ypu want to test this with phenidone and ascorbate, just mix a PC-developer and omit the ascorbate. Then you have a developer just like a PC-develper with oxydated and useless ascorbate. Use a carbonate alkali that places the pH at about 11.2.

    Hint: 0.15g phenidone per 1000ml.

    Check if you can get a ISO-100 B&W film developed in 6.5 minutes @20C with that.

    If you get good development without the ascorbate I will shut up and never dispute this.
    Hint: You won't!

    Add 6g ascorbic acid and do a new test.
    This time you will get good development i 6.5 minutes@20C.

    Do a new test. This time with 6g ascorbic acid in the pH 11.2 carbonate solution.
    Check if you can get a ISO-100 B&W film developed in 6.5 minutes @20C with that.
    Hint: You won't!

    But as I initially said, This TCB developer DOESN'T contain any phenidone or your friend "Fenton", so when and how fast phenidone are oxydated isn't of ANY interest with this developer.

    I suppose that you are trying to twist the discussion over to that theme because you haven't anything to discuss about this developer.

    That is hand waving or smoke and mirrors to me.

  8. #18

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    Quote Originally Posted by Gerald C Koch View Post

    Since TCB contains no chelating agent to prevent Fenton oxidation its keeping properties will be poor as compared to Xtol and other formulas that do use a chelating agent.
    Who is Fenton?
    I don't care if Fenton is oxydized, because he isn't in any way connected with this developer.

    Tylenol, ascorbate and alkali.
    NO "FENTON" whoever or whatever that is.

    I have read a lot of books about developers. I also has worked in a photo finishing lab for aan extended time.

    I have NEVER heard or read the word Fenton in any realation to developers.
    Stick to correct or well-known names on the chemicals involved.

    Your statement about Fenton is just a method of twisting the thread away from the original issue and over to a issue you want to discuss.
    That is the way you want to "win discussions" on the net.
    Smoke screen?

    Start your own thread about "Fenton" if you want to discuss him.
    Last edited by Tronds; 12-02-2011 at 05:20 PM. Click to view previous post history.

  9. #19

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    Quote Originally Posted by Photo Engineer View Post
    I am not aware of any great degree of synergy between phenidone and ascorbate.
    In this article, http://unblinkingeye.com/Articles/Sy...synergism.html , Patrick Gainer has a graph of the synergy between phenidone and ascorbate, based on the ratio of ascorbate-to-phenidone. He found that the curve began flattening at around 40:1, and was quite flat at 80:1.
    Any comments on his work?
    I'm also aware that phenidone doesn't need a partner for development, as in POTA.

    Mark Overton

  10. #20
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    OXIDATION, for Christ's sake!

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