is Potassium Alum same as Potassium Chrome Alum?

Discussion in 'B&W: Film, Paper, Chemistry' started by consumptive, Sep 27, 2012.

  1. consumptive

    consumptive Member

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    I need to make a hardening fixer for using with liquid light and was thinking of Kodak F6. Formula says to use "potassium alum". I've got an old kodak glass bottle labeled "potassium chrome alum" [purple crystals inside] and was wondering if anyone knew if this was the same as the "potassium alum" in the Kodak F6 formula?

    Alternatively, does anyone know a good non-rapid hardening fixer to use with liquid light? Thanks.
     
  2. Ian Grant

    Ian Grant Subscriber

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    No quite different, both are used as hardeners but Potassium Chrome Alum needs extra care the Chromium can cause issues with broken skin and also breaks down in fixers. It' can be used as a hardening stopbath. Kodak published a formula. Don't add it to a fixer though.

    You can add a fesw drops of Chrome alum solution to the Liquid light prior to coating they used to suggest this anyway.

    Potassium alum is easy to get hold of btry a chemists (dru store).

    Ian
     
  3. Alessandro Serrao

    Alessandro Serrao Member

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    No.
    Potassium alum is potassium aluminium sulfate KAl(SO4)2 while potassium chrome alum is chromium potassium sulfate KCr(SO4)2.
    With a non hardened emulsion you need a glutaraldehyde hardener, such as Rollei RBM5.
     
  4. Photo Engineer

    Photo Engineer Subscriber

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    You can use the Potassium Chrome Alum in the following way....

    First, make up your fixer without the hardener. Then, make up a 10% Potassium Chrome Alum.

    Here is the modified process sequence.

    Develop
    Stop or rinse in running water
    If you use a stop, then rinse in running water
    Chrome Alum 10% for 5 minutes at 20C
    rinse 5 min at 20C
    fix in your non-hardening fixer
    wash
    dry

    This will harden most anything.

    An alternate with LL is as follows:

    Harden 10% Chrome Alum 5 mins
    wash 5 mins
    develop
    stop or rinse
    fix in non hardening fixer

    There are several more prehardeners for LL such as:

    Formalin 3&% 10 ml
    Sodium Sulfite 50 - 100 g/l
    Sodium Carbonate 25 - 50 g/l
    pH to 10.0

    Have fun.

    PE
     
  5. jsmithphoto1

    jsmithphoto1 Member

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    If i were to make a 10% solution as a presoak, how much use until exhaustion?
     
  6. Photo Engineer

    Photo Engineer Subscriber

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    This is difficult to determine except by observing hardness in the rest of the process.

    One book I read suggests that you can judge exhaustion by the fact that the Chrome Alum solution begins to turn grey from the normal "grape" color.

    PE
     
  7. Gerald C Koch

    Gerald C Koch Member

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    I have only seen chrome alum used as a stopbath and not as a presoak. As a presoak it might interfere with development. Chrome alum loses its hardener capability when contaminated by sulfite due to carryover. The is indicated by a change in color from purple to green.
     
  8. Ian Grant

    Ian Grant Subscriber

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    I prefer to use a Formalin/Formaldehyde pre-hardener. I also added a few drops of formaldehyde to developer immediate before use for a commercial application.

    When I first started using Adox/EFKE film in the early 1970's I initially used a Chrome alum hardening stop-bath, but switched and much preferred using Formaldehyde in the developer, I can't remember what developer I used, it wasn't my normal replenished system.

    I think Gerald's right that pre-hardening affects development but that's overcome with consistency. By that I mean pre-hardening will have an effect but once you know by how much you compensate for it.

    Ian
     
  9. Photo Engineer

    Photo Engineer Subscriber

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    A wash before development will prevent interference with hardening. If little or no wash is used, you can destroy both the hardening and the development.

    If used after development, the same thing holds true. Use a good wash.

    However, one must remember that softening takes place in the developer due to wetting and swell and therefore, there may be no option but to harden before development.

    PE