Darkroom Humidity Control

I've decided to try to get better control of humidity during coating

and drying of paper for Pt

printing. All the gurus seem to suggest close to 50-55% is the ideal.

Problem is, in Baltimore,

90% humidity is the rule in the summer, and < 20% is not unusual in

the winter. I've pretty

much given up using home-use humidifiers and dehumidifiers to try to

control the whole

darkroom: even the larger units seem to affect the humidity by no more

than 10% or so either

way, and a truly climate-controlled environment is beyond my reach

financially. So, I just want

a "chamber" big enough to store and dry 12X20 paper pre and

post-coating. Web searches for

things like "humidity chamber" turn up devices costing $10,000 aimed

at industrial uses. How do

all of you on the list maintain humidity accurately, given the need to

lower and raise it quite

substantially from ambient? Presumably a box with a bowl of water in

it won't help much when

ambient humidity is 92%! I have a Radio Shack hygrometer, for what

it's worth, so I can

measure the humidity in the darkroom to +/- 2%. The darkroom is in a

pretty dry basement,

about 300 square feet of floor space.

 

Thanks in advance for any help you can offer!

 

Nathan

Nathan: My experience has been that a small air conditioner in a reasonably small darkroom drops humidity something like 15 to 20%, so that won't get you all the way to where you need to be in the summer. On the other hand, on dry winter days, it is easy to raise humidity very dramatically and quickly. Put a dishwashing-type sprayer on your darkroom sink, turn on the hot water, and spray water back and forth across your sink, this works quickly and dramatically to bump up the humidity. I've done this before I load filmholders on very dry days and it works. Humidity will stay fairly high if you leave the door closed and no fan on. Good luck with what you're doing.

My vote is for central air conditioning. I have been printing Pt/Pd for over ten years in North Carolina (State motto: "It's the humidity.") Air conditioning is a way of life here. Never had any problems summer or winter. Then again, I'm not making large prints like you are.

Nathan, thankfully I dont have that problem here, 60 to 65 % year round. I am so glad I moved from Houston. Anyway, I was going to suggest why not use the trick cigar sellers use. Build a wooden box, seal the sides with glue, not only screws, and place a humidity gauge and a little plate with water inside. I know my cigars are kept this way and are at a constant 60%. Of course here is not a problem but in houston it sure was..:-))

Nathan, here's a website with an interesting suggestion on humidity control:

 

<a href="http://www.mikeware.demon.co.uk/platin.html"

>hyperlink</a>

Nathan,

 

I never had to deal with too much humidity, but dry it is in

Colorado. I put a small "cold" air humidifier, $30, (the kind that

won't leave condensation on your hand if you hold it over the

outupt) in the bottom of my 5' Arkay film drying cabinet. This

stayed at a nice 48-55%, btw the film dryer was not on. I had

success with this technique, but now.....You didn't ask for this, I

now coat, let it sit untill a sort of semi-gloss finish, and put it

under a small window fan on low. The key now is pulling it from

the fan with just the right humidity left in the paper, which for me

is when it's cool to the touch. I was way too spun out about

humidity stuff before Kerik Kouklis showed me this technique.

My space is anywhere from 15-35% depending upon the time of

year, and I can print at anytime without waiting for paper to

humidify. It has saved me A LOT of time and the prints look

great!

 

mateo

Golden, Co

Nathan,

 

I'm a bit surprised that you aren't able to move the humidity by more than 10% in the basement. Normally, basements are the best location for a darkroom because the climate is tempered by the walls that are in contact with the ground. They also tend to have much less infltration than an above-ground room will have, which makes it easier to move the humidity.

 

Several thoughts come to mind. Do you have finished walls and floor in the basement? (That is, are the walls and floor sealed?) If you don't then you may never be able to reduce the humidity due to water vapor migrating through the concrete and block. If you don't I would recommend sealing all the surfaces.

 

Do you have a radon abatement system? This will also extract moisture from below the slab and make it easier to adjust the humidity. It's another good reason the seal the walls and floor (to reduce the migration of radon particles into the space). I don't know if radon is a problem in the area of MD that you live or not.

 

Do you heat the basement? If so, turn off the heat during the summer months. A warmer basement equates to a greater amount of moisture carrying capability in the air (in an absolute sense). So, if the air in the basement is cold (say 65-68) and then you come down to work in the darkroom, the dehumidifer and the Nuarc, etc will warm it up. As the temperature goes up, the relative humidity will go down, as long as you aren't adding additional moisture to the space. This is because relative humidity is a ratio of the amount of moisture in the air to the total amount the air can carry at that temperature and pressure. (OK, I've tipped my hand, now everyone knows that I'm an engineer by training.)

 

Your darkroom space is about the same size as mine, and I was able to drop the humidity today from 82-84 down to the mid 50's in an hour or so. That was done with a decent mid-range dehumidifer. The temerature also went up in the space from 68 to approx. 74 or so by the time I was finished printing. I keep the darkroom door closed and the other room in the basement is noticably cooler and more damp.

 

Finally, while humidity is a factor in the speed of the platinum emulsion, it does not appear to have a real significant difference on the end result. The only place that it rears it's ugly head that I have seen is with some papers, and the quality and eveness of the platinum coat they will make. It appears that low humidity is a problem, but I haven't seen complaints related to high humidity.

 

Platine is one that has problems with low humidity, and Lenox is another. I'm sure there are many others out there that are affected in a similar way. Platinotype, however, appears to be very forgiving WRT humidity, as I have printed in the middle of winter and the middle of summer and not had problems that I could attribute to humidity.

 

---Michael