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  1. #21
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    Fulvio;

    Sorry, but I warned you about the denaturing agent. Many of them are not good for emulsions.

    Here, thymol is used in moutwash. It is rather common.

    PE

  2. #22
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    Fulvio:
    Photographers' Formulary carries thymol, if you can't find some locally.

    http://www.photoformulary.com/Deskto...ion=0&langId=0

  3. #23
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    Sorry, I should have mentioned that, but your being in Europe I couldn't think how to get any there. Thanks Denise.

    PE

  4. #24
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    Let me clarify a point regarding washed and unwashed emulsions.

    1. I can duplicate the picture result I previously posted in contrast, tone and speed either washed or unwashed from the same starting bromide formula, but the final addenda that I add and the finsih are different for the two.

    2. A washed emulsion can be used on any FB paper, but cannot be used on RC, film or plates with good results.

    3. A sulfur finish is required for a bromide emulsion if you wish to have any degree of speed and contrast.

    I hope this helps those reading about making emulsions.

    PE

  5. #25

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    Quote Originally Posted by rongui View Post
    "Overripening leads to fog and loss of speed and contrast. You must stop this ongoing process by using proper stabilizer.

    I bet commercial liquid emulsions are all washed, and probably all bromide based."


    I was looking at the MSDS of Liquid Light and noticed that besides the bromide and chloride, there was trace amounts of Cadmium salts.

    Are the Cadmium salts used for contrast increase, reduction of fog, and would the Cadmum salts act as a stabilizer?

    Just one loud remark: I AM NOT ADVOCATING USING CADMIUM SALTS IN SMALL LAB EMULSION PRODUCTION. They are very toxic and bad for the envirnment.
    Do you have that MSDS in PDF form? How recent is it?

    Cadmium salt is most typically used in chloride and chlorobromide emulsion. Depending on the amount, it can affect the grain size, speed, image hue, and tonality. In old formulae, Cd was used in warm tone contact and enlarging paper to increase the highlight contrast of emulsion. For this purpose, some other ripening restraining agents work just as well. Cd was also important part of lith film formula, because classic hydroquinone-only lith dev's worked best with chlorobromide emulsion of about 20-30% bromide doped with cadmium salt and sulfur sensitized (but not gold). Alternative methods were developed for this type of emulsion.

    I wonder if Liquid Light is really chlorobromide using cadmium. That would be a bit surprising. Chlorobromide emulsions are much more sensitive to chemical contamination and a lot more easily ruined, compared to bromide emulsions.

  6. #26
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    Cadmium can be added at either of 2 points in making an emulsion (Cl/Br). It can be added during precipitation or after precipitation, just before coating. The amount used is different for each case. In any event, its use has been superceded by organic compounds with low toxicity and low environmental impact.

    Liquid Light still lists Cd in the MSDS and a number of European and Asian companies still use Cd (last I looked).

    PE

  7. #27

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    Quote Originally Posted by Ryuji View Post
    Do you have that MSDS in PDF form? How recent is it?
    This MSDS is currently on Rockland's website. The link is: http://www.rockaloid.com/msds.html#LL

    Thanks for all of the replies.

    rongui

  8. #28

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    mmm apparently something is not working

    I bought some pure ethyl alcohol and added 5 ml in a 125 ml potassium bromide solution with about 20 g of food gelatin. The bromide gelatin was stored in a light tight bottle in the fridge.

    The next day I melted the gelatin and heated some silver nitrate solution (20%) to about >40°. After the gelatine melted I went in the darkroom and under safelights poured some silver nitrate in the bromide gelatin (at 1:1 ratio). I started with just 20 ml (10 ml gelatin + 10 ml silver nitrate sol.). I mixed the whole thing until became white.

    I coated the papers immediately after mixing.

    The sensitized papers didn't work though. When placed into developer without any exposure to light, they became dark brown colored (a "rust" tone). It goes without saying that for exposed papers happens the same. But the same happened with the bromide gelatin prepared with denaturated alcohol. So, perhaps denaturated alcohol wasn't the problem.

    The recipe was the same as the emulsion that worked in the first place but didn't keep well for more than a few days. Except that now I used separate solutions for each of the two components and I have mixed them only before coating papers. Also, I didn't use tap water, but distilled water. Could be something wrong in the mixing stage? Temperatures of each solution?

    I don't think the silver nitrate is bad... I used the same solution of silver nitrate for some very nice POP prints this evening and they were just fine.

    I just noticed that when I poured the silver nitrate into potassium bromide some precipitate formed and was very hard to dissolve. It looked like ordinary silver bromide precipitate, but in the previous batches I didn't notice such bigger "grains" of precipitate. They partly dissolved at the end of the mixing stage.
    Last edited by Fulvio; 12-06-2006 at 04:15 PM. Click to view previous post history.

  9. #29
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    It could be that there is a reducing agent in the paper you are using, or it could be that you have gone into silver excess. If you add more silver than halide, the emulsion will fog.

    Without gelatin to 'peptize' the silver halide, the crystals will be very large and will settle to the bottom. The siver halide formed in the absence of gelatin or with too little gelatin will be very foggy.

    PE

  10. #30

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    I said before in this thread: Ethanol is not going to prevent bacteria from breaking down gelatin molecules. 5ml in 125ml of ethanol is completely ineffective for this purpose. Get a better biocide or give up on the idea of pre-dissolving gelatin. Once the gelatin is deteriorated by bacteria, what you observed will happen.

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