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  1. #61

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    I'm not sure which part of my statement conflicts with Hrst's results, but I'm not keeping close track either. All I meant was that divided developer no longer has much effect for contrast control, and it used to before I started chromes in the mid-late 90s, and that the amount of hypo is not critical, eg 1/4 or 1/8 t should work (but see PE's earlier comments on that, I am not any sort of chemist).

  2. #62
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    Too much hypo or variable hypo can cause variable contrast and dmax in the yellow (top) layer. This can extend to other layers depending on level.

    Just wanted to be clear.

    PE

  3. #63

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    Any progress?
    Any good kitchen recipes?
    I ran a batch from an old kit this week, the first third of the run was good, but then the bleach seemed to fatigue and got bad really quick (both with fresh and "semi-replenished").

  4. #64
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    I started experimenting with developers, trying to get rid of that red-cyan crossover, but it seems it can be quite a difficult task, at least for me :rolleyes:. By adding more bromide, I've been able to decrease the red-cyan crossover but it changes to magenta-green crossover.

    I've found that thiocyanate (KSCN or NaSCN) can give quite a nice masking effect that lowers contrast and gives a boost in shadows.
    Attached Thumbnails Attached Thumbnails thiocyanate.jpg  

  5. #65

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    I've been looking for phenazine and quinoxaline--various forms are available (or at least advertized) by some supply houses at various prices that make random experimentation less attractive.
    A couple questions:
    1. which forms of these are suitable (or best) for bleach?
    2. better sources?
    3. is the catalyst actually consumed in the process (if so, it should not be called a catalyst!) or is the really low pH lost--in other words, would replenishing the acid restore the activity?

    The last I should be able to check for myself, but I didn't think about it in time last time I ran a batch.

    4. Since the P3 components are available, at least putatively, has anyone tried using the bleach with Dektol and regular fix?

  6. #66
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    I have a 1g sample of Phenazine from Spectrum that just arrived. Due to the extremely hot weather, I have not done any experiments with it. I hope to get a sample of the Quinoxaline soon.

    They are true catalysts and are not consumed in the reaction. The dye is reduced and the Silver is oxidized. If you use Sulfuric Acid, the reaction forms two Amine fragments which form a salt with the acid and the Silver forms Silver Sulfate.

    PE

  7. #67

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    So, adding a little H2SO4 might prolong the usefulness of the bleach? (Linear kinetics on the catalyzed reaction? Increase time with further dilution of the reagent? Reaction to precipitate out the salts? so many interesting questions...) Aim for pH of 1?

  8. #68
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    I suggest reading some of the patents on Dye Bleach granted to Ciba in the 60s and 70s. There are dozens of formulas that use many different acids. The pH is generally less than 3. IDK if just adding acid will "replenish" the bleach because Silver Sulfate is formed and dissolves to some extent in the bleach rendering it less capable of bleaching more Silver metal.

    PE

  9. #69

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    Quote Originally Posted by Dr. no View Post
    4. Since the P3 components are available, at least putatively, has anyone tried using the bleach with Dektol and regular fix?
    And also, does the bleach in the P30 kit have extra capacity (ie. does the limiting factor in the capacity of the kit have to do with the fix/developer?)

  10. #70

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    The pool of acid in Ilfochrome bleach is quite large. As the catalyst is indeed regenerated in the process, the major cause of exhaustion involves loss of the silver ligand (I-) which drives the equilibrium toward dye fragmentation. Loss of the antioxidant will also lead to aerial oxidation of the ligand. There is however another major consideration: When the catalyst is used alone in a bleach composition (especially with the very active phenazines), the dye destroyed is super-proportional to the amount of silver present. The result is an image which is VERY high in contrast. The same super-proportionality exists in chromogenic developers such as the E-6 color developer. Thus, the need for citrazinic acid as a competitive coupler to reduce contrast in E-6 becomes obvious. Ilfochrome bleach utilizes a competitive oxidant which will remove silver in the same fashion as ferric-edta, WITHOUT reducing the dye. This simultaneous competition allows a lower contrast image to be obtained, along with the removal of ALL SILVER at the conclusion of the bleach treatment. Therefore, another major cause of bleach exhaustion would be decreasing concentration of the competitive bleaching agent.



 

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