Brain Storm: Drying "cabinet" for sensitized carbon tissues...

holmburgers · Sep 2, 2011

Hey all,

So in my new place I can darken my laundry room when I need to process film and paper, but I can't really keep that room dark for any extended period of time; more than a couple of hours.

But I need a UV-free place for my sensitized carbon tissues to dry. My thought is to create some kind of box or similar thing that I can put the tissues in and store somewhere out of the way.

First thought is to get an under-the-bed rubbermaid storage thing and place a large sheet of metal in it, securing the sheets with magents and storing under the bed. I'd get something that's opaque and put some kind of ventilation in it and maybe even have a small fan to circulate air.

But it needs to be safe, as in chemical contamination, and I guess this shouldnt' be a huge concern since there are no fumes or anything.

Anyways, could use your guys collective brain power to solve this problem.

Thanks!

gmikol · Sep 2, 2011

I use a Technal forced air print dryer to dry my sensitized tissues, and, with different racks, actual prints. It has a fan-only setting, plus a heated setting. It can accommodate up to 11x17 sheets. I have it sitting in a room with a north-facing window with the blinds down and shut, and a relatively thin curtain drawn over it (certainly not blacked-out). Haven't noticed any fogging as a result. Painting the plexiglas cover of it opaque black would probably allow me to be even more casual about where I put it.

With brush sensitization, I typically only need 1.5-2 hours to dry a tissue. With a stronger or more directed airflow, I could probably cut that time down a little more.

--Greg

John Jarosz · Sep 5, 2011

I have a cheap metal filing cabinet - the flimsy kind you get at office depot. I hang my tissue to dry and when they feel right I put them into plastic ziploc bags and then into the filing cabinet. I take them out as I use them in the printing session. The ziploc bags prevent them from drying out more as time goes by. This is not long term storage - only for the printing session.

Edit - I use alcohol or acetone to speed the drying of the tissue. Mine will dry in 2-3 hours. If you use thick tissue you may need much longer even with alcohol or acetone

nsurit · Sep 6, 2011

Although I haven't used it for the purpose you are seeking to accomplish, I have an old Burke & James Drying Duo drying cabinet for both prints and negatives. It is 24" X 34" X 12" and has multiple screens to put stuff on to dry. This is not an offer to sell as I have no interest in selling it, however you might keep your eye out for one. It would get you stuff dry quickly and then you could store it in a light tight box. It is a fairly old piece of equipment and probably could be had for a decent price if you can find one. Mine came from a university photo lab. Bill Barber

mdm · Sep 7, 2011

I dry mine in a cupboard with a dehumidifier running to keep relative humidity to 30-40%.

holmburgers · Sep 7, 2011

Thanks for all the ideas guys. The dehumidifier, or some kind of heating element seems like a good idea, and I think I just need to go thrift shopping to look for the right kind of cabinet.

Jim Graves · Sep 8, 2011

I use my laundry room for sensitizing also ... and use the clothes dryer for drying the sensitized tissues. Not too practical if you're a high-volume printer but I only sensitize about twice a month at most and only print up to 8" x 10" negatives on 9" x 12" tissues.

I run the dryer for a few minutes to get the interior temperature to around 90 degrees F ... turn it off ... rotate the drum by hand until the vanes align on the bottom so I can put a rack across them ... tape the light switch on the door down so it doesn't come on when I open the dryer ... load the sensitized tissues onto the rack one at a time as I finish each ... wait two hours from when the first tissue went in and start printing.

There is no air circulation or fan to assist with drying but I brush sensitize with acetone and have not had a problem with them drying. The dryer will hold ten 12"x15" tissues at a time ... but the most that I've done at once is eight 9"x11".

For light protection, I use cutouts of amberlith over the windows ... that lets plenty of daylight in but no UV ... rubylith would work too but is a little darker and you get less light to work by.

holmburgers · Sep 9, 2011

Jim, another great idea!

holmburgers · Feb 14, 2012

A brief update to this thread.

Last night I took a vintage paper filer (kinda like this one) and wrapped it with black plastic sheeting. By taping the plastic around the corners I can hopefully keep all the light out, and then a loose flap allows for loading it, using magnets to secure that once it's loaded.

My one concern is getting airflow throughout. I've got a sample of black Tyvek coming, which if it's sufficiently light proof should make a nice "breathable window".

The metal filer is appealing because I can use magnets to attach my carbon tissues, though they curl so strongly I've had to order neodynium magnets! The metal can easily be hosed down too, to prevent any dichromate contamination.

If the black Tyvek is sufficiently light blocking, it might be a good material to use in place of black plastic, since it lets water vapor through.

On the other hand, if it doesn't work, I need to find a better way to get air in and vapor out. Trying to think of some kind of simple light-trap, but so far I'm a bit stumped...

greybeard · Feb 14, 2012

You could consider picking up an old refrigerator for next to nothing (or less) and using trays of dessicant instead of a dehumidifier. If the door gasket is decent, it will be light-tight, and the interior finish lends itself to easy cleanup. For hanging paper, remove all of the shelves but the top one, or install your own hanger bars. For flat storage, use the existing shelves or add your own---with the refrigerant removed and the power cord cut off, you can safely drill into the cabinet to mount things.

If the interior is going to be crowded (we can only hope!) the easy, safe way to get air circulation is to use a 12 VDC electronics fan powered by an AC adapter located outside the reefer. In a closed environment, it won't take much to keep the air stirred up.

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.

gmikol · Feb 14, 2012

greybeard said:
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

paul ron · Feb 15, 2012

Raw rice makes a good desicant as well.

fotch · Feb 15, 2012

High quality = (there was a url link here which no longer exists)

holmburgers · Feb 15, 2012

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...

Hexavalent · Feb 15, 2012

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.

nsurit · Feb 15, 2012

Would a Jerky Maker or food dehydrator work?

holmburgers · Feb 15, 2012

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(?)

gmikol · Feb 15, 2012

holmburgers said:
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.

holmburgers said:
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

holmburgers · Feb 15, 2012

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/search.aspx?searchtext=desiccant selection 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.

gmikol · Feb 15, 2012

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

holmburgers said:
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

Mainecoonmaniac · Feb 15, 2012

Here's a food dehydrator.
http://www.harvestessentials.com/weston-food-dehydrator-75-0201-w.html

greybeard · Feb 15, 2012

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.

This is what I was referring to by "conditioning"; some specified moisture content may not be particularly sweet, but if it affects the chemistry, it would be nice to have it the same every time. "Fully" dehydrating (silica gel, molecular sieve, etc.) for storage and then conditioning to a predetermined moisture content (calcium nitrate slush, etc.) might be a worthwhile technic. I haven't worked with carbon tissue, but I understand that it is plasticized with sucrose, which would seem to be most effective if not completely dry.

Regarding refrigerators, I was thinking of the dorm-room size, or maybe one of the under-the-bar refrigerators.

gmikol · Feb 16, 2012

^^^ Exactly.

But since you're going to condition the tissues, might as well figure out what the optimum moisture content is.

--Greg

holmburgers · Feb 16, 2012

Also, assuming you have "completely" dehydrated a tissue, how long would it take to acclimate to the ambient moisture? Couple minutes, an hour or two, ...?

Did I catch a pun in there... sweet spot and sucrose?

gmikol · Feb 16, 2012

holmburgers said:
Also, assuming you have "completely" dehydrated a tissue, how long would it take to acclimate to the ambient moisture? Couple minutes, an hour or two, ...?

I would guess it would be on the order of hours. Might depend on how hygroscopic your additives are. If you had an analytical balance, you could completely dry the tissue, weigh it dry, and then monitor it's weight over time and see for yourself. Balance would probably need to be sub-milligram accurate.

This is just conjecture on my part, but I suspect it would be quicker to drive a tissue with excess moisture to equilibrium than a completely dry tissue to the same equilibrium point. Since heat could be used with a damp tissue to drive water from the tissue, but I'm not sure that a warm environment could be used to drive moisture into the tissue.

holmburgers said:
Did I catch a pun in there... sweet spot and sucrose?

NO...I only use glycerin, no sugar.

--Greg

Brain Storm: Drying "cabinet" for sensitized carbon tissues...

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