Kodak Single-Powder Developers.

Discussion in 'B&W: Film, Paper, Chemistry' started by Keith Tapscott., Oct 7, 2007.

  1. Keith Tapscott.

    Keith Tapscott. Member

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  2. Photo Engineer

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    I think those patents should help you and everyone understand the situation.

    In the ones I know, the HQ and Metol are milled such that they form a core particle with sulfite surrounding them, or carbonate, or borate. This forms a protective coating.

    Then they are sealed in the bags with dry nitrogen or something like it.

    The compounding process is very complex and sensitive. I have actually never seen it as it goes on in closed containers, but I've had it described to me by two of the people from P&S (powders and solutions). That division was responsible for making up the chemistry.

    PE
     
  3. Keith Tapscott.

    Keith Tapscott. Member

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    Hello PE,

    Wouldn`t there be some kind of reaction with a developing agent coming into contact with sulphite, borates and carbonates etc?:confused:
     
  4. Photo Engineer

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    Well, developing agent will not normally react with sulfite in the absence of oxygen. Both sulfite and HQ react with oxygen. But under nitrogen, you can form small beads of encapsulated developer under a shell of many chemicals. This is what is done in manufacture.

    Sometimes, the shell is just an inert material.

    HQ is not reactive with borate either in the absence of oxygen. At most, it will form a borate salt which is 'good'. I'm not sure about metol, but it is proteccted in the beads as well. I know that much.

    Some of this is done with molten materials such as hot liquid HQ or sulfite in a molten slurry of some sort. As I said, I have had it described in general, but have never seen it. It is highly secret and everything went on in closed containers of nitrogen. They had their own research division that developed the packing methods.

    I can suggest looking under Surash among others for Kodak patents in this field, but I've forgotten most of the names.

    Don't worry. It works. I prefer working with and on, liquid kits myself. That is where I did most of my work with P&S.

    PE
     
  5. Keith Tapscott.

    Keith Tapscott. Member

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    Thanks, I was simply interested in how this was done that`s all.