Recently, I found a "dehumidifier" product called "damp gone" in the local
hardware store. The cost is low, a few US dollars for 12 ounces (340 grams),
so I bought it and am trying it out. The maker is Rutland Products of Rutland,
Vermont, USA, and the product number is "item # 620". (I have not seen local
sources of the silica drying granules.)
The material looks and smells like kitty litter, which is made of clay. The
warnings on the container say that it contains calcium chloride, so the most
likely composition is clay plus calcium chloride, made into a granular form.
(One could make this oneself, simply by soaking kitty litter in a calcium
chloride solution. Calcium chloride is sold during the winter as a sidewalk
deicer in many hardware stores.)
One prepares damp gone by pouring the granular material into a pyrex baking
dish and baking it in an oven for one hour at 400 degrees farenheit (200
degrees C), after which it becomes noticably lighter. The instructions say to
repeat this drying process when the weight doubles, which is a lot of water.
After an hour cooling, the granular material is put back in its muslin bag.
If one puts calcium chloride crystals plus a saturated solution of same in
water into a closed container, the relative humididty will be 31% to 35%,
depending on temperature, with higher temperatures leading to lower values of
humidity. When the crystals are all dissolved, the drying effect ends.
Calcium choride in clay should do much the same, depending on how much calcium
cloride is used. But, it's cheap, so they probably use as much as will work,
and doubling the weight is a lot of water.
So, putting 12 oz of damp gone in a hermetically sealed container of a few
cubic foot capacity should allow the internal humidity to be controlled for a
very long time. The limitation is probably how many times one opens the
container.
The only disadvantage is that calcium choride will corrode metal, and so if the
damp-gone dust gets into the gear, problems could result. The use of clay
greatly reduces the problem, but still one worries, especially given that we
expect our obsolete but beloved gear to last decades.
So, my current solution is to put the damp-gone bag at the bottom of the
container, put some kind of floor with feet over it, and pile the gear on top
of this floor. That way, the dust stays below. One caould also put a cotton
towel on the floor, to act as an added dust barrier. This solution works only
for static storage, not for portable use.
If one built a storage cabinet for humidity control, I would put two doors in
it, a large one above, and a small one below, so the moisture absorbing
material could be taken out, dryed, and reinstalled, all without disturbing the
gear. If there are two bags of material, one can dry them one at a time,
ensuring continuous coverage even while drying. The floor between the two
compartments would have a fabric barrier.
Joe
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