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  1. #1

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    Some pre-emulsion making questions . .

    I'm about to give a go at making a basic emulsin to coat on glass for my 13x18 plate camera. I've assembled all the bits and pieces (including a magentic hot plate stirrer) and have a coupe of questions.

    1. If my darkroom safe light (red) is safe enough to not fog paper for several minutes, is that dark enough for emulsion mixing purposes? How do I know if the light is OK? I don't want to mix in the dark . . .

    2. All the recipes say to add silver to the gelatin slowly, to increase the speed. A quick dump increases contrast at the expense of speed, as I understand it.

    If I like the idea of contrast more than speed, is it OK to do a quick add? How slow would that likely make the final product? Any idea?

    3. There are a variety of recipes to try, each with slightly varying amounts of silver nitrate to gelatin to pot. bromide/iodide. Is there a guideline that suggests more silver is better/worse, contrasty/less contrasty, faster/slower, etc? I'm trying to decide which recipe to do first.

    4. Most recipes call for thymol as a preservative. I don't have that yet. Is it absolutely crucial, or can i do a batch without it, and still expect some longevity from the emulsion? Or should I wait until I get it?

  2. #2
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    Hi Kami,

    First: Congrats! on taking the plunge. You're going to have a blast.
    Here's my take on your questions:

    1) If you mean commercial enlarging paper, I'd say you're probably safe. It's tricky, though. I had the same little red safelight for years; the incandescent kind covered with red film. It worked great. When it finally blew I could only get one that was covered in what looked like red paint. It took me three weeks to figure out it was a fog machine. I replaced it with a string of tiny LED Xmas lights. My darkroom is lit up like it has a red sun and I've never fogged anything since. There is no reason to work in the dark.

    2) Given mid-day summer sun (i.e. good UV light), you won't go much lower than ASA 3 or higher than ASA 25 with a basic bromide emulsion without extra sensitizers. They are inherently contrasty. The speed of addition, combined with the temperature and the amount of mixing during ripening, influences grain size (i.e. 'speed'). You can push up the speed a bit and lower the contrast a bit without risking heat/ripening fog, but mostly it is what it is. If at some point you want to try for more speed or a smoother density scale, I've found that divided additions is better and more predictable than adding one addition slower. Make sure you follow the temperature recommendations and don't let the heat climb too high with an emulsion recipe that calls for ammonia.

    3) The amount of silver to gelatin is mostly about how thin you can coat your plates and still get decent density. Again, the best advice is to follow the recipe exactly the first couple of times and then try a few changes to see what works technically and aesthetically for you personally. With the old recipes, I think it's best to start out rich. A higher % gelatin will be easier to handle while you are learning. Gelatin is essentially free and a gram or two difference in silver won't have much effect on the cost of making the recipe. When you start to customize your recipes the only trick is to remember to change the silver and the halide in the same proportion.

    4) You do not need a preservative. Your emulsion won't be sitting around in the refrigerator long enough to grow mold! Don't fall for the temptation to make big batches. Your learning curve will be a beautiful thing to see if you make many, frequent recipes. And, if you screw up one, you won't waste more than a couple of bucks .

    The best of luck and fun,
    d
    www.thelightfarm.com

  3. #3
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    Almost any red safelight that works for your enlarging papers will work for your hand made emulsions. A film emulsion generally has a lower contrast than a paper emulsion by the very nature of things. So, it gains its speed and lower contrast by having a slower addition time of silver to salts. Higher temperatures increase speed and lower gelatin increases speed, but if you go too high in temperature (~80C) or too low in gelatin (~1%) you will get poor results.

    Plan on coating your emulsion between 5 and 10% for best results.

    PE
    Last edited by Photo Engineer; 03-26-2010 at 08:15 PM. Click to view previous post history. Reason: As Denise said!

  4. #4
    dwross's Avatar
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    Ron,

    I think your goal of brevity (usually an admirable goal!) resulted in a couple of typos. As a general rule, decreasing the silver addition rate will lower the contrast of an emulsion. Also, 80C is almost certainly too high for an ammoniacal emulsion, the most commonly encountered type in old film recipes. 40-45C is about as high as I'd want to go to avoid fog.
    d

  5. #5
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    Denise, boiled emulsions at 95C were common in the early part of the last century. They were not ammonia emulsions.

    Since ammonia was not mentioned, I used that example, as temperature is a valid "knob" with or without ammonia the absolute upper value depending on ammonia. I make ammonia emulsions at 60C without fog problems.

    I made the correction to clarify my remarks. Thanks.

    PE

  6. #6
    dwross's Avatar
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    Well, I can see right now that I spend waaayyy too much time with my nose in dusty old emulsion books. I'm becoming a fact-checking, fact-arguing geek . Do you ever watch Big Bang Theory? The guys in the comic book store arguing about story arcs? J.M. Eder in 'Modern Dry Plates', 1881, describes ammonia in emulsions. He talks about keeping the temperature not much more than 40C, but notes that Capt.Pizzighelli (Captain Sweatpants!) claims the character of the particular gelatine employed "exercises considerable influence.., while one sample of gelatine will stand digesting for fifteen minutes with ammonia at 70C, another will produce a foggy emulsion if a temperature of 50C be employed." (p21) And, further up the timeline, both Baker and Duffin recommend 40C-45C.

    From all that, I'd say you might have been lucky with fog. A novice just starting out might be advised to err on the side of caution and keep the temp low.

    Geekfully submitted for your consideration,
    d

  7. #7
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    Denise;

    Inactive gelatin has leveled the playing field in a sense. Also, they never heard of TAI. I suggest that you check the class notes.

    PE

  8. #8
    dwross's Avatar
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    Kami,

    Pay absolutely no attention to all this nonsense You'll make a beautiful emulsion. Think making bread: You can bake a delicious loaf with all-purpose flour from the grocery store, or you could listen to a couple of obsessive-compulsive foodies argue blue about the relative virtues of high mountain spring wheat from Montana vs. Tuscan something-or-another. They just might drive you to Wonderbread!
    d

  9. #9
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    Very good Denise.

    I don't disagree in one way, but I do in another.

    Best wishes.

    PE

  10. #10

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    Quote Originally Posted by dwross View Post
    Kami,

    Pay absolutely no attention to all this nonsense You'll make a beautiful emulsion. Think making bread: You can bake a delicious loaf with all-purpose flour from the grocery store, or you could listen to a couple of obsessive-compulsive foodies argue blue about the relative virtues of high mountain spring wheat from Montana vs. Tuscan something-or-another. They just might drive you to Wonderbread!
    d
    Thank you both for all the advice! It is appreciated.

    And Denise, especially, thank you . . . I've spent hours at the Light Farm reading and rereading all your info. It's what given me the confidence to give this a try.

    I've decided to try Mark Osterman's recipe as outlined on your site for my first go . . . My goal is to have plates in the camera by the Easter weekend!

    Thanks again!

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