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  1. #1
    Dr Croubie's Avatar
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    Does mixing-speed in precipitation-step matter?

    Hi all,
    So I'm following the 'Kitchen Emulsion' recipe(s) from thelightfarm and I've nearly got all of my ingredients to start, all I need now are Glyoxal and Gelatin (well, I've got some McKenzie's cooking Gelatin, but I'll try to find some real photo-grade stuff here).

    Next thing I need is the mixing implements. Seeing as I'm going to buy something anyway, I'm looking at two options:
    Option 1 is a 'milkshake maker', something like this.
    Advantages are that I can mount the motor/base above the waterbath/crockpot, and just pick it up to reach the stirring bit. I can use any size/shape of jug/glass to hold the emulsion (I'm thinking a nice Pyrex measuring jug with a handle to make it easier to both hold and wipe clean.
    The disadvantage that I can see is that the stirring end is only really a disc, acting sort of like a reverse Testla Turbine. Is that a disadvantage? I'm not sure how viscous this stuff is meant to get. Also, if the jug doesn't have a lid there's a potential for splashing.

    Option 2 is a Stabmixer, and using either the Whisk attachment or using the chopping-container.
    With the whisk, it's much the same as the milkshake maker, except that it's a whisk instead of a disc, and I can keep the emulsion-jug in the waterbath and lower the whisk in.
    With the chopper-container, I can leave that in the waterbath and just start the stabmixer when needed, plus I can drill a hole in the lid of that to put the syringe into. But then it's a blade going through the emulsion. Plus those things are a bitch to wipe clean, I envisage wasting a lot of emulsion.

    So the one thing I don't know about is the speed of these things. Stabmixer with chopping-container would generally go slowest from my experience with these things. Whisk might not go so fast, but with more wires going through the emulsion it's probably more violent. Milkshake maker is only a disc so the least violent, but to move milk it probably makes up for it in speed.
    All that thelightfarm says is with the hand-mixer option, to put it on the lowest speed. I can probably hack the speed of whatever I buy but I'd prefer not to if I can just use it as-is. I'm a bit more concerned now about how violent it's going to be depending on the mixing attachment, or doesn't this matter so much?

    Any other suggestions?

    (also, if anyone knows where to get Photo-grade gelatin and/or Glyoxal in Aus without ridiculous shipping costs, feel free to let me know...)
    An awful lot of electrons were terribly inconvenienced in the making of this post.

    f/64 and be there.

  2. #2
    Photo Engineer's Avatar
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    Mixing speed controls speed and contrast to a certain degree.

    What do you want to do? You can stir, mix or homogenize. The things you refer to can do all of these 3 things, but if you get to homogenization or the like, you end up cracking crystals and making fog. A blender can be too vigorous for an emulsion. I suggest a propeller mixer at about 300 rpm. You can get them at paint or hardware stores and use them on a drill if you can control speed.

    PE

  3. #3
    Dr Croubie's Avatar
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    Quote Originally Posted by Photo Engineer View Post
    Mixing speed controls speed and contrast to a certain degree.

    What do you want to do? You can stir, mix or homogenize.
    Thanks, that's kind of what I was getting at, just couldn't think of the way to describe it (now that I've had an hour nap I feel a lot better and clear-headed).
    The word 'emulsion' to me means something like mayonnaise, and I know how finnicky that can be to make (but delicious when I do, I'm presuming home-made emulsions are just as rewarding).

    I was thinking along those lines, that being too vigorous is a bad thing. What are the dangers of under-mixing / just stirring?

    I hadn't thought of a drill, but I've certainly got a few of those, a nice big drill stand and a dremel rip-off too. Paint-mixer like one of these? I've got one but I should probably buy a clean one without all the paint on it...
    An awful lot of electrons were terribly inconvenienced in the making of this post.

    f/64 and be there.

  4. #4
    kb3lms's Avatar
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    Yes. Like that. Mine is similar but shrouded. Consider getting a small 12v dc geared motor in the 300-500 rpm range. I got mine through Amazon for about $10. Then you can use a bench power supply to control the speed. A drill is really overkill, if it would even work.
    All this has happened before, and all this will happen again.

  5. #5
    dwross's Avatar
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    Or you can just use a kitchen hand whisk. My Oster mixer has a very slow speed. That's still quite speedy, but the emulsions turned out fine. I don't use that method myself anymore because either a hand whisk or a magnetic stirrer are easier and I'm personally simplifying and standardizing all my recipes and darkroom work flow. The point of that line of articles is that you don't require fancy lab equipment. I do need the Oster for mixing up baryta base (made some just last night), so equipment is rarely wasted. Besides, it's hard to deny that playing with different tools is part of the fun of all this!

    In the middle of this page is a video of using a hand whisk to mix the emulsion. http://www.thelightfarm.com/cgi-bin/...tent=26Jan2013
    www.thelightfarm.com
    Dedicated to Handmade Silver Gelatin Paper, Film, and Dry Plates.

  6. #6
    Photo Engineer's Avatar
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    If mixing is too slow, large "fast" crystals form and you get more pepper grain. Contrast is lower due to a broader distribution of crystal types and sizes. If mixing is too fast, you beat foam into the gelatin and you also can crack grains leading to fog. Crystals tend to be finer and of a more uniform shape and this leads to higher contrast.

    This differs from what I would say if you asked me about addition rate of the silver nitrate to the salt.

    PE

  7. #7
    kb3lms's Avatar
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    What ever method you use,during precipitation I would say you want to stir "briskly" so that the ingredients are well mixed. Not like a blender and not slowly. Well mixed is what you want.
    All this has happened before, and all this will happen again.

  8. #8
    Photo Engineer's Avatar
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    OTOH, mixer head type and speed do matter. I am wrestling with an emulsion which needs 6000 RPM for good results and for that I had to get a Kodak style mixer. I still am working on this one!

    Make sure that under about 400 ml for a make, you use either a magnetic stirrer or a propeller mixer. Above about 400 ml, you have to use both to prevent the bottom of the make from not getting enough mixing. This is using a hotplate for making.

    PE

  9. #9
    dwross's Avatar
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    Hi Ron,

    It's been my understanding that silver halide crystals are very hard to "crack". Really tough tiny puppies. I can find plenty of references to emulsion fog from contaminants, from excess heat and/or ripening time, and from not enough halide or gelatin during precipitation, but not from physical damage. My library stops at 1979 (Haist's 2 vol. set) because that's probably the practical limit to what I can accomplish at home. Are you referring to risks with modern machinery and techniques? What kind of mixer and speeds are we talking about here?

    re air in the emulsion. That certainly can happen! Fortunately (in my experience), it's easy to exclude foam, if you get it, by pouring the emulsion through a 'gold' metal coffee filter. After that the little bubbles remaining in the emulsion float up and out when you re-melt the set emulsion, especially if you add (and I always do) ethanol/Everclear.

    Good luck with your new emulsion! Fun!
    www.thelightfarm.com
    Dedicated to Handmade Silver Gelatin Paper, Film, and Dry Plates.

  10. #10
    Photo Engineer's Avatar
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    Denise, the early t-grain emulsions were so fragile that when the film was wound around the tiny 120 camera rollers the grains cracked. Emulsifiers and blenders can crack even large K-grains if run fast enough and that is why the Kodak PEPA has no blades so it mixes well without cracking. Yeah, we had a lot of problems "cracking" that problem. We no longer used prop mixers either due to the high speeds needed to make the more modern emulsions.

    The foam certainly is reduced by filtration, but I am talking about foam present during the addition of silver nitrate. That causes bubbles on the surface in which a 2D model of pptn. takes place forming odd crystals when you don't want them and it also exposes the forming grain to the atmosphere over a large surface area. These are not the bubbles that may be present during coating.

    PE

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