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  1. #11

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    Quote Originally Posted by greybeard View Post
    Incidentally, if you want to "condition" paper, there are various salts which, when in contact as both solid and saturated liquid, will maintain a constant humidity level until either the solid has dissolved in captured water or the liquid has given up its water to the environment. Much simpler and cheaper than a humidifier/dehumidifier setup with a control loop.
    This is what I hope to do at some point in time. Modify an old forced air-print dryer to either maintain constant humidity, or with the addition of a bed of silica gel, to fully desiccate the tissue for storage prior to sensitization.

    Here's a link describing various salts and humidity levels.

    http://www.omega.com/temperature/z/pdf/z103.pdf

    --Greg

  2. #12

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    Raw rice makes a good desicant as well.
    Anyone can make a Digital print, but only a photographer can make a photograph.

  3. #13
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    Items for sale or trade at www.Camera35.com

  4. #14
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    I can see how a refrigerator would make a great box, but for my purposes I'm afraid I need something smaller and more portable (space is an issue). However, a desiccant sounds like a very appealing alternative to air-flow.

    I guess Epsom salt (magnesium sulfate) is a good choice, if dehydrated sufficiently in an oven beforehand. I'll probably give this a go.

    That omega link is a bit heady...

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    Chris, you state that this drying cabinet is for sensitized tissue. I assume you will be using acetone or IPA in the mix, in which case you do want ventilation - dessicant alone will not do the whole job, and a box of acetone/IPA fumes is probably not a good thing.
    - Ian

  6. #16
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    Would a Jerky Maker or food dehydrator work?

  7. #17
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    For now I was planning on just using a water solution without solvent; choosing to abandon the spirit variable at present.

    But a great point Ian... these dessicants won't absorb solvents, only water!

    Would a Jerky Maker or food dehydrator work?
    If you could make it light proof, I guess it'd work fine. I wonder if high heat might fog the tissues though(?)
    Last edited by holmburgers; 02-15-2012 at 11:31 AM. Click to view previous post history.

  8. #18

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    Quote Originally Posted by holmburgers View Post
    I guess Epsom salt (magnesium sulfate) is a good choice, if dehydrated sufficiently in an oven beforehand. I'll probably give this a go.

    That omega link is a bit heady...
    Well...I don't see MgSO4 on the list, so it's tough to assess how effective it would be. Keep in mind that those salts listed will maintain a given RH in a closed environment when the salt is in a "slush" with water (i.e. far less water than required to dissolve all the salt).

    I'm not sure they're the right choice for desiccating a tissue. Silica gel is far superior for that purpose, and it can be "recharged" in an oven, as well.

    Quote Originally Posted by holmburgers View Post
    That omega link is a bit heady...
    Just ignore the text on how they collected the data. The tables are pretty straightforward...the RH the salts maintain varies with temperature, some are more stable with temperature, and some less. Since most people work in a relatively narrow range of about 15C to maybe 30C, the temperature variation is less critical.

    Also, keep in mind that completely dry un-sensitized tissues improves their keeping qualities. But sensitized tissues need a little moisture in them to improve their printing speed. I don't know if anyone has ever collected any data to see if there is a "sweet spot" for moisture content of a sensitized tissue.

    --Greg

  9. #19
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    Magnesium sulfate should be good; I see that it has an efficiency equal to silica gel, and potentially higher(?). It's rechargable too.

    Here, follow this link and open the PDF there... http://www.avantormaterials.com/sear...election guide

    This "sweet spot" intrigues me... I wonder if completely dehydrating them and storing them in the fridge (safely sealed of course) would allow you to store them for several weeks. Then when you're ready print, you could take them out and let them acclimate to the humidity level of your house.

  10. #20

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    Thanks for that link. I saved it into my file of all things photographica.

    Quote Originally Posted by holmburgers View Post
    I wonder if completely dehydrating them and storing them in the fridge (safely sealed of course) would allow you to store them for several weeks. Then when you're ready print, you could take them out and let them acclimate to the humidity level of your house.
    If you mean after sensitization, then yes, this is possible. I am aware of some printers who do this, but it's generally regarded that freezing does a much better job of preserving sensitized tissues than just the refrigerator, especially if you're looking at the "several weeks" scale of time.

    Keep in mind that there is a "dark reaction" with dichromate and gelatin that is slowed (but not stopped) by fully drying. It is slowed much more effectively by temperature. Though the time scale and the mechanism itself is very different, conceptually, it's the same idea as storing your film at room temperature vs. the fridge vs. the freezer.

    --Greg

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