Pot Bromide 10%

Discussion in 'Contact Printing' started by RPippin, Oct 7, 2010.

  1. RPippin

    RPippin Subscriber

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    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.
     
  2. lxdude

    lxdude Member

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    Ooooohhhh... I thought the thread title was Pot Brownie! :redface:

    I was gonna say 10% might be a bit much...
     
  3. Ian Grant

    Ian Grant Subscriber

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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% :D

    Ian
     
  4. RPippin

    RPippin Subscriber

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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.
     
  5. lxdude

    lxdude Member

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    Far out, man...
    :D:D:D
     
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  6. Gerald C Koch

    Gerald C Koch Member

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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.
     
  7. RPippin

    RPippin Subscriber

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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?
     
  8. clayne

    clayne Member

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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.
     
  9. RPippin

    RPippin Subscriber

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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.
     
  10. c6h6o3

    c6h6o3 Member

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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.
     
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  11. RPippin

    RPippin Subscriber

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    Thanks, I checked and i'm using the same R40 flood, Canadian G2, and about 40" above the table, so it must be an issue with the developer. My negs are also a bit thin, so I'm going to try some 4X5 negs that are a bit more contrasty. Although I've not shot with Super XX or TMY, I do have some negs from FP4 that I developed in HC110. Lately I've been using WD2D+, so my negs look a bit thinner than with other developers. I use a digital timer and set it for however many seconds I get after doing a strip test. I'll keep at it with the advice I'm getting till I get it right.
     
  12. DanielStone

    DanielStone Member

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    try a LOWER WATTAGE BULB.

    I've found a 30w to be a good alternative

    -Dan
     
  13. c6h6o3

    c6h6o3 Member

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    For Azo or Lodima?
     
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  15. c6h6o3

    c6h6o3 Member

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    I doubt it. It sounds like your negatives are too thin.

    Don't confuse contrast with overall density. My negatives have less contrast than most, not more, because I place my shadows on Zone IV. I expose more and develop less to compress the scale from the bottom up. You need density, not just contrast. I also think that a staining developer helps. Pyrocat HD is a great one. So is ABC pyro.
     
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  16. DanielStone

    DanielStone Member

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    mostly for enlarging papers, since that's what I can afford right now. Set about 36" above the contact frame, and with a sheet of white bedsheet as a diffuser material under the bulb(clamp-light from wal-mart, $7)

    haven't used azo or lodima yet, but I've read that Lodima is faster in amidol than Azo, canadian or other runs

    -Dan
     
  17. c6h6o3

    c6h6o3 Member

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    If you haven't used Azo or Lodima yet, what do you mean by 'mostly'? To my knowledge they and the new Fomalux are the only contact speed papers around.

    From the Kodak B&W Darkroom Dataguide, 1988: The ISO paper speed of both Kodabromide and Elite Fine-Art enlarging papers was 320 at grade 2. Grade 2 Azo has an ISO paper speed of 4. That's more than 6 stops difference. I don't think a 30 watt bulb will quite cut it for a silver chloride contact speed paper, which is what RPippin is using.

    Azo was invented at the turn of the 20th Century. You want an old fashioned, plain incandescent bulb. It doesn't do well with modern UV-accentuated bulbs such as the ones they make for illuminating indoor gardens to accelerate plant growth. The frequency spectrum of your bulb is more important than the wattage.
     
  18. RPippin

    RPippin Subscriber

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    Thanks c6h6o3, I do have some 4X5 negs that have the density you speak of, so I'll try them out. There seems to be very divergent ideas about lights, which adds to my overall confusion. The light I use is one that was recommended by other photogs that do contact printing, yet I get a lot of advice to use regular incandescent bulbs. That seems to fit with the logic of what was available back in Westons day, I just don't know. Like most problem solving it could be one of the elements, exposure, developer, or negative, or a small combination of each. I need to narrow it down by getting rid of one of these as the cause so I'm not wasting time chasing down the wrong path. Your comments are very helpful and much appreciated. Thanks again.
     
  19. Sal Santamaura

    Sal Santamaura Member

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    Jim, I'm curious about this. Other than resulting in longer print exposure times, why would a denser negative, assuming the less dense one it's compared to already has shadows high enough to be off the toe, make any difference?

    I have many thousand sheets of Azo stockpiled. When I print on them using a 40-watt bulb in a 10-inch Smith Victor reflector with attached diffuser (18 inches above the frame), using negatives developed in non-staining developers, my times are around 20 - 25 seconds. I can't see any visual difference in prints made from negatives that were accidentally overexposed even further.

    Thanks in advance.
     
  20. clayne

    clayne Member

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    He might be wanting to compress highlights and then expand them at the printing phase.
     
  21. Sal Santamaura

    Sal Santamaura Member

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    I don't think so. Jim shoots TMY (perhaps now TMY-2), so he's probably got lots of straight line curve for highlights regardless of increasing his exposure. Jim?
     
  22. c6h6o3

    c6h6o3 Member

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    I find that I get deeper blacks, and for some reason a nicer print color when I use my combination 300 watt light bulb and space heater. But if you can't tell any difference, I'll try a smaller wattage. Those 300 watters are getting hard to find. Thanks for the tip.

    And you're right about TMY. It has a lot more straight line than any paper can handle. Its characteristic curve is quite similar to that of Super XX. Personally, I wouldn't trade TMY or TMY-2 (I have both) for Super XX. I'm astonished that so many photographers prefer a non T-grain film. T-grain seems to me to be quite the superior technology.
     
  23. c6h6o3

    c6h6o3 Member

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    So if RPippin is getting overexposed prints at much shorter exposure times with a non-diffused 30 watt bulb, wouldn't you agree with me that his negatives are probably thinner than yours?
     
  24. Sal Santamaura

    Sal Santamaura Member

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    Yes, but if he simply exposes his negatives more without changing film development time, I don't think he'll see any difference in the prints' appearance, unless the original negatives were not off the film's toe. Otherwise, only his print exposure times will increase.

    PS One difference in his prints might be that paper area outside the image is blacker. No impact on the low image values though.
     
  25. c6h6o3

    c6h6o3 Member

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    Yeah, but isn't that what he wants? I think his original complaint was that the times he had to use were too short to give adequate control.
     
  26. RPippin

    RPippin Subscriber

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    The bulb I'm using is a 300 watt R40 that was recommended by another contact printer from Richmond. it sits 40" above the print frame in a flood light housing. I haven't had time to get back in the darkroom till now (shot the wedding from hell this weekend), but I'm going to start over with a exposure test, proper soup, and see what kind of times I get then.