I have a geochemica called the Water town History Cache. The container is quite large and had a problem of moisture getting into the box, causing rust and the possibility of mold to start growing on the log book. I planned this cache for nearly two years, so that was unacceptable. I wasn't about to have the cache container ruined! Someone told me about desiccants, which will absorb moisture, and suggested I check out a marine supply shop.
I searched on the web and determined that it would be more effective if I were to just make my own. Because I did not see many other sites out there that said how to do this, I also wrote up this page to help others.
A desiccant (or sometimes misspelled as a dessicant) is a material that removes moisture from the air. It does this through a process called adsorption. No, not absorption. There is a tiny difference: materials that absorb water literally take it into themselves, but materials that adsorb water just have the water molecules stick to the surface.
Most of the desiccants you find on the web today use silica gel as the main agent. Some may use clay and others use different chemicals. Silica gel is often used by crafters to dry flowers quickly. You can also use borax (check the laundry aisle in your local store) and other chemicals. I've read that silica performs really well and can adsorb moisture pretty fast, plus you can get indicator crystals that tell you when the silica has adsorbed as much as it can hold. From what I have read, silica gel can hold up to 30% of its weight in water. It can also be recharged and reused by sticking it in an oven (see below).
These instructions can let you build a desiccant container, desiccant bag, or other similar device. Heck, you can just put the silica gel into a paper cup and that may be good enough.
If you can't sew or use sharp objects, just stop here.
Silica gel is pretty harmless. If you try to not breathe the dust and if you wash your hands after use, you should basically be safe. If you start caughing, you're probably breathing in too much dust. A chemical sheet on silica gel would say the following:
May cause mechanical irritation to the eyes and skin.
May cause irritation of the digestive tract if ingested.
Dust is irritating to the respiratory tract if inhaled.
Prolonged exposure to inhaled dust may cause delayed lung injury/fibrosis (silicosis).
But really, the stuff is pretty darn safe, otherwise I would certainly not use it in my geocache.
These instructions tell you how to create a desiccant bag. Other tips are listed below in case you want a container or something else. The bag made in this process has a vinyl side so you can see the indicator crystals and know when you need to "recharge" your reusable bag.
Silica Gel - You can get this from your local hobby store. It is used for drying flowers. Make sure to get "indicator crystals" in with the silica. They will turn from blue to pick, telling you when you need to recharge your desiccant bag. Also, silica gel comes as particles, not as an actual gel.
Cloth - I have some muslin in the picture, but you may wish to have something a little more dense. Perhaps an old cotton shirt would work. You do not want to let the silica out.
Vinyl - I have some medium weight vinyl, which will let me see the indicator crystals on one side of my bag so I know how much moisture was adsorbed. You can use cloth on both sides if you do not intend to look at the colored bits that indicate how much water was absorbed.
Sewing Machine - If you can't operate one, then find someone who can. This is just a basic pocket or bean bag, so you can hand sew it if you like.