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  1. #1

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    Potassium hydroxide -vs- Sodium hydroxide

    I'd like to attempt to make a contrast reducing mask for a color negative as described by Ctein in his book "Post Exposure." He recommends using Tmax 100 film developed in a special developer that produces a thin, but still color neutral, negative. The developer formula calls for potassium hydroxide, which I don't have, but I do have sodium hydroxide and am wondering whether I could substitute? I know nothing about chemicals, but see that the two of these are listed as "closely related" on a couple reference sites.

    Also, if anyone has experience making masks for color film, either by Ctein's process or an alternative, I'd sure appreciate any tips.

    Thanks,

    -Michael

  2. #2

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    masks

    Poco-there's an excellant article in this months PhotoTechniques about making
    masks. I'll leave it up to you to see if it is for you. Me-I'm going to learn how to do it.
    Best, Peter

  3. #3

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    Article

    Poco-if you can't find the article Pm me and I'll get it to you
    Peter

  4. #4

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    While sodium hydroxide and potassium hydroxide are similar in their chemistries, potassium compounds are usually more photochemically active than their sodium counterparts. Substituting sodium hydroxide would cause the developer to be less active. Potassium hydroxide is not expensive and can be ordered from several companies that supply small amounts of chemicals to hobbiests.

  5. #5

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    Thanks, Gerald, I plan to order some, but was wondering whether I had the ingredients to experiment while I'm waiting. I may still do so with juiced up sodium hydroxide levels.

    Peter, is that article about masking for color film? For color I guess it's important to get a neutral toned mask, which isn't a huge concern for B&W.

  6. #6

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    For all practical purposes:

    NaOH: Molecular weight 23 (Na) +17 (OH) = 40
    KOH: MW: 39.1 (K) + 17 (OH) = 56

    Therefore, for 1g of KOH = 0.71 G of NaOH, ignoring K versus Na counter-ion effects.



 

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