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  1. #11
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    It depends on how much silver is in that 40 grams of gelatin, not on how much gelatin is present.

    For example, if you have an emulsion with 10 grams of silver halide / 40 grams of gelatin and another with 20 grams of silver halide in 40 grams of gelatin, if the grain size was the same in both cases, they would take different amounts of hypo. If grain sizes differed in either case, then the amount of hypo would change again.

    So, hypo goes up as silver goes up and hypo goes up as grain size goes down.

    Since it varies from emulsion to emulsion, this becomes an exercise in experimentation, finding out how much hypo to add, how hot to heat the emulsion, and how long to hold it. For heat and time, I suggest 60 degrees C for 30 - 60 minutes with hypo present, for amount of hypo, I have no exact value.

    For starters, you might try 25 - 50 milligrams of sodium thiosulfate pentahydrate for every mole of silver present, and work up or down from there as needed. It should be added as a 0.1% solution in water and should be made fresh.

    PE

  2. #12

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    Quote Originally Posted by robopro View Post
    Yes, it is, I know, but I'm afraid if I start trying to get too technical I'm going to show off my ignorance even more than I am now! :-).
    Everyone has to start somewhere, so don't be afraid. Exposing ignorance can be embarrasing but you at least learn something and don't do any harm.

    I'm a little too busy to try it right now but I've been thinking I may try making a gelatin emulsion. Of course it won't be on the level you guys are doing, but what the heck? I copied 4 recipes off the web and have read about a dozen patents and I think I'm starting to get at least a basic feel for it. Also think I might try using sodium thiosulphate to try and bump the speed up. One patent I read called for adding 6.7 grams of 1% solution to every 2000 grams gelatin and ripening at 50C for an hour. I managed to break that down to 1 small drop for every 40 grams.
    One of the recipes I found calls for 2 ripening periods, 1 for 2 hours and 1 for 1.5 hours, so I'm thinking I should add it during the second phase.
    What do you guys think?
    The real, short answer is that you can't tell from that info. You need to consider a whole procedure to figure out the range of thiosulfate you should use. Even so, it often requires some experimentation to figure out the optimal level. The optimal level can change depending on the gelatin impurity, temperature of precipitation, duration of precipitation, amount of salt used during precipitation (especially at the beginning), and A LOT of factors. Seriously. The detail gets long, but this is because the optimal amount of thiosulfate added for chemical sensitization (digestion) depends strongly on the crystal structure (cube, octahedral, tabular form of octahedral, or tabular form of cube, etc.) and also strongly on the grain size. The detail is always a long story when it comes to the topic of emulsion sensitization, but it doesn't require a lot of work to make a slow emulsion (ASA single digit). (If you want to make ASA three digits emulsion, you better learn all the latest tricks in this.) More of a problem for you is that emulsions that are sensitized with sulfur only typically produce strong highlight contrast and poor shadow details. (Look at photographs taken before gold technique was used and you'll know what I mean. If you make your own emulsions and try you'll actually experience this.) For camera negative emulsions, it is best to use gold plus sulfur technique, which is quite a bit more involved, but will give MUCH better shadow rendition. For faster emulsions, you need reduction, gold plus sulfur technique, which is CONSIDERABLY more involved...)

    If you begin with print emulsion, your life will be a lot easier, because you can make quite practical emulsion of good tonality and speed with sulfur only sensitization.

  3. #13

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    Oh -- that's it -- make it as hard on me as you can!

    :-)

    I know I've got a LOT to learn -- that's one reason why I joined this forum. Why try to reinvent the wheel? But, when you're talking about gelatin ASA of 6, then my albumen must be around a 2. ASA 100 would be great, but then I don't really feel like getting a degree in photo chemestry and turning my basement into a laboratory. I can always stick in a piece of ASA 400 sheet film for protrait work. Uh, do they even make 400 sheet film?

  4. #14
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    Yes, they make ISO 400 sheet film.

    Sulfur sensitization will get you into the ISO 25 - 100 range, and will give good contrast with many emulsion types. The trick is to get the right level of sulfur, and coat the right level of silver. Among other things, making the right type of emulsion helps to start with and exposing in mid scale avoids any sharp toe that may result.

    The whole process can be as easy as dump and stir, once you get the initial conditions ironed out. It would be best to use an emulsion formula supplied in a text book such as "Silver Gelatin" rather than doing it all yourself from scratch. After all, why reinvent the wheel.

    PE

  5. #15

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    Quote Originally Posted by robopro View Post
    Why try to reinvent the wheel?
    It is exactly reinventing the wheel. And it won't be anything like what Fujifilm makes and sells for a couple of bucks a piece.

    To me the only reason to make emulsion is to make something that's good but unavailable from any manufacturer. When I want results I can get with commercial products, there is absolutely no point of making the material myself, because I will not save time OR money in doing this. If Tri-X in sheet size will do the job, your time and money are better spent with it.

  6. #16
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    I have to agree with Ryuji. That is why I have concentrated on Azo paper, and a Kodabromide/Brovira paper. But, OTOH, there is such a thing as being prepared.

    That is why I am developing a simple film emulision with a 40s look or thereabouts, to be ready for those who want such a film and also to keep the technology alive. I am also doing it because it can be done, and done simply in a darkroom.

    PE

  7. #17

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    Quote Originally Posted by Ryuji View Post
    It is exactly reinventing the wheel. And it won't be anything like what Fujifilm makes and sells for a couple of bucks a piece.

    To me the only reason to make emulsion is to make something that's good but unavailable from any manufacturer. When I want results I can get with commercial products, there is absolutely no point of making the material myself, because I will not save time OR money in doing this. If Tri-X in sheet size will do the job, your time and money are better spent with it.

    By reinventing the wheel I meant why try to invent my own emulsion from scratch without finding out how others have done it first, avoid their pitfalls and benefit from their experience? If I was going to design my own clock, I'd first take a couple of other clocks apart and see how they worked, then start on mine.
    And I certainly would never try to build my own clock to save time or money -- but just to point at it and say 'I made that!'
    If I ever start doing ULF portait work I probably will use sheet film cuz I'll need an ISO of 400 or so. But then I'll have to design a better shutter...

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