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Thread: Pot Bromide 10%

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    RPippin's Avatar
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    Pot Bromide 10%

    Not being a chemist, I'm a little lost on how to get 10% Potassium Bromide from the stuff I've bought from Formulary. it's a combination of solids and pellets in a plastic container, but does not say if it is a "percentage" of anything. I'm assuming the solids need to be desolved and mixed with distilled water, but how then do I get to the gram amounts that I need. It would make sense to me that the chemicals already are a 10% makeup and all I need to do is measure out the appropriate amount of grams. Just want to be sure. Thanks.

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    lxdude's Avatar
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    Ooooohhhh... I thought the thread title was Pot Brownie!

    I was gonna say 10% might be a bit much...
    I do use a digital device in my photographic pursuits when necessary.
    When someone rags on me for using film, I use a middle digit, upraised.

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    Ian Grant's Avatar
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    If it's solid then you add 100g to water and make up to a litre , or 10g to 100ml water. At the moment it's a solid so 100%

    Ian

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    RPippin's Avatar
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    Thanks guys. And dude, 20% in brownies isn't that much, just don't over do it and eat to much.

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    lxdude's Avatar
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    Far out, man...
    Last edited by lxdude; 10-07-2010 at 11:21 AM. Click to view previous post history.
    I do use a digital device in my photographic pursuits when necessary.
    When someone rags on me for using film, I use a middle digit, upraised.

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    You don't say how much KBr you purchased. To make a 10% w/v (weight/volume) solution you would dissolve X grams of solid in enough water to make 10X milliliters. So if you purchased 100 grams of KBr you would dissolve this in enough water to make 1000 milliliters. If you purchased 50 grams then you would use enough to make 500 milliliters. For a 10% solution every milliliter will contain 0.1 gram of solid.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

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    RPippin's Avatar
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    Thanks Jerry. Can I pre mix the KBr from the solids and keep a 10% solution for use at a later time? How long is the shelf life?

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    clayne's Avatar
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    Any typical 10% solution in water is based off of the fact that 1ml water weighs 1g. So targeting a 1L 10% solution, ~900 ml water, 100g of whatever, add water to hit 1L if it isn't already.
    Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.

    http://www.flickr.com/kediwah

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    RPippin's Avatar
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    O.K., now that I've got the chemical thing down, the other issue I've had is my prints are way to dark, with to little time under the light. I have a UV, 150 watt bulb in a bowl shaped reflector from Lowes sitting about 40" above the print frame. The times are around 3 seconds with Azo G2, and 1 1/2 seconds with G3 Lodima. From what I've read, I've been leaving the prints in the developer to long (2 to 2 1/2 min), but I still think there is a problem with the exposure. I should be needing longer exposures. I don't use a diffuser, but will try that next.

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    c6h6o3's Avatar
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    If your Azo was made in Rochester (that is, from any master roll except the last one, which was coated in Canada) you should not develop any longer than 1 minute in amidol. Any Lodima is also a 1 minute paper. I use a 300 watt incandescent bulb suspended 3' above the printing frame and my exposure times range from 10 to 60 beats of the metronome using a 100 beats/minute cadence. Your problem might be the fact that you're using a UV bulb. Try a plain old incandescent light bulb, preferably an R40 flood, such as this one. Azo and Lodima are very sensitive to UV wavelengths.

    Even if your Azo is Canadian, the maximum development time is 2 minutes. Most of my prints on Canadian grade 2 develop best at 1'40". Also, you need a denser negative for silver chloride paper than for enlarging paper. That's why Super XX and TMY work so well with it. With those films you can slide your whole scale up the straight line portion of the curve without the shoulder (and there's almost none with these films) clipping the highlights.
    Last edited by c6h6o3; 10-08-2010 at 04:31 PM. Click to view previous post history.
    Jim

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