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  1. #21

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    I'm just observing and I'm excited! Who knew reinventing the weel could be so interesting?

    - Justin

  2. #22
    Photo Engineer's Avatar
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    Ok, based on the results I see in the pictures, the emulsion formula you have was designed for active gelatin and is therefore giving you low contrast and low speed.

    The safelight is ok. The fog level may be due to the amount of silver coated or to overwashing, IDK. It might also be the amount of iodide used.

    Try adding 100 mg of sodium thiosulfate pentahydrate to each mole of silver nitrate used in making the emulsion. (just work out the math, I'm too lazy this early in the AM) Do this to the final washed emulsion. Then heat the emulsion to 60 degrees C and hold for about 60 minutes. (you may want to sample it at 30 and 45 mins to check for fog. Stop the treatment if the fog seems to be going up too rapidly. This adds sulfur sensitization to the emulsion. See Jim Browning's formula here for similar treatment.

    This can add up to 5 stops in speed and up to 2 grades in contrast.

    PE

  3. #23
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    Quote Originally Posted by Photo Engineer View Post
    Ok, based on the results I see in the pictures, the emulsion formula you have was designed for active gelatin and is therefore giving you low contrast and low speed.

    The safelight is ok. The fog level may be due to the amount of silver coated or to overwashing, IDK. It might also be the amount of iodide used.

    Try adding 100 mg of sodium thiosulfate pentahydrate to each mole of silver nitrate used in making the emulsion. (just work out the math, I'm too lazy this early in the AM) Do this to the final washed emulsion. Then heat the emulsion to 60 degrees C and hold for about 60 minutes. (you may want to sample it at 30 and 45 mins to check for fog. Stop the treatment if the fog seems to be going up too rapidly. This adds sulfur sensitization to the emulsion. See Jim Browning's formula here for similar treatment.

    This can add up to 5 stops in speed and up to 2 grades in contrast.

    PE
    Cool! I should note that the formula does explicitly state inert gelatin.. But I'll try the sulfur sensitization anyway. I don't know what it'll do if I don't try.

    I also am going to do the rough wash tests you were talking about in a previous post.

    Thanks
    Vincent Purcell
    Lexington KY Photographer + Media Artist
    http://vincenttpurcell.com

  4. #24
    Ian Grant's Avatar
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    Maybe there's a language problem here. "Inert gelatin" is not necessarily de-activated or oxidised gelatin.

    The term "Inert Gelatin" here in the UK refers to a type of laboratory gelatin used for biological applications, and it means Biologically inert. The formula comes from a British author.

    Ian

  5. #25
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    Quote Originally Posted by Ian Grant View Post
    Maybe there's a language problem here. "Inert gelatin" is not necessarily de-activated or oxidised gelatin.

    The term "Inert Gelatin" here in the UK refers to a type of laboratory gelatin used for biological applications, and it means Biologically inert. The formula comes from a British author.

    Ian
    Ah. I knew I should've brushed up on my British English first!
    Vincent Purcell
    Lexington KY Photographer + Media Artist
    http://vincenttpurcell.com

  6. #26
    Photo Engineer's Avatar
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    All photograde gelatin today in England, France and the US (AFAIK) is both inert and oxidized as well as being calcium free and neutral.

    In the 40s, none of the above were true. One of the first operations with gelatin was to balance pH with Magnesium Oxide or the like, then the ripening was determined, and then it could be used. Today, I can pretty much take samples from Kodak, Gelita and Rousselot and get pretty much the same result with no special precautions.

    From the first test, I can then tweak the emulsion formula and go on from there.

    PE

  7. #27
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    Congratulations!! Jadedoto,

    It's such fun, isn't it. I love how you're sharing your excitement. If you have the time and/or inclination, please share with us on hybridphoto.

    Keep up the good work (actually, I prefer "Keep up the good play")

    Denise Ross
    Last edited by dwross; 08-27-2007 at 02:00 PM. Click to view previous post history. Reason: typo

  8. #28

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    Quote Originally Posted by Photo Engineer View Post
    All photograde gelatin today in England, France and the US (AFAIK) is both inert and oxidized as well as being calcium free and neutral.

    PE
    You mean all the stuff that we, as amateurs, can buy?

    I have been told, by someone who would know, that some manufacturers still use active gelatines, with the sulphur compounds intact, in their emulsions. This means there are gelatine maunfacturers (in the UK certainly) that can provide active gelatines, but only in industrial quantities...
    (I've been investigating )

    Maybe one day there will be enough of us on this thread to club together and buy a few tons?
    Last edited by steven_e007; 08-28-2007 at 04:39 AM. Click to view previous post history.
    Steve

  9. #29
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    Steve;

    There are some companies that do use active gelatins, I'm sure but for the most part the open market only supports the oxidized and inert photograde gelatins.

    If you do get an active gelatin, you will have to test each batch for activity. It usually comes in 3 grades or weak, medium and strong, referring to their effects on sensitization. Each grade will vary from batch to batch.

    Home experimenters will be having enough problems maintaining a constant speed and contrast without introducing another set of variables. It is much easier to maintain one stock of oxidized photograde gelatin and add a measured standard amount of hypo solution than it is working with the old gelatin.

    PE

  10. #30

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    Quote Originally Posted by Photo Engineer View Post
    Steve;

    It is much easier to maintain one stock of oxidized photograde gelatin and add a measured standard amount of hypo solution than it is working with the old gelatin.

    PE
    Ok, I'm convinced by that!

    Is there a post on here somewhere that tells us how much hypo to add to the gelatine and at what stage?

    Are we talking about plain sodium thiosulphate?

    Are there other sulphur compounds that are used?

    Thanks,


    Steve
    Steve

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