Silica Bags As Desiccants: Do They Work?
I frequently receive mics where a small silica crystal bag is tucked into the mic box.
The idea: to let the hygroscopic (moisture seeking) silica pull excess humidity from the mic, especially from the capsule, whose performance is greatly affected by humidity.
But simple logic dictates that there are only so many moisture-starved silica crystals in these tiny pouches, and, unless you severely restrict the amount of humid air getting in contact with the silica, the dehumidifying effect will be essentially over once the crystals have sucked enough moisture, neutralizing their ability to suck more - about 2-4 hours.
Only intelligent management of the process can make the idea work: Severely restrict the amount of moist air the silica bags are exposed to!
If you have a fully charged (i.e. moisture-starved) silica pouch of big enough size to be effective (at least 3-4 inches square), place the pouch against the mic’s head basket, then wrap a sealable plastic bag tightly around the mic (a rubber band can assist in sealing).
This limits the air available to the silica crystals.
How do we know when the silica pouches have neutralized? Silica crystals usually have a chemical added that will change the crystals’ color once the chemical comes in contract with humidity and the crystals are moisture-saturated.
Usually, dry crystals are dark blue, or another strong color, and neutralized crystals (those which can no longer absorb additional moisture) turn towards neutral or slight pink or brownish.
Reconstituting Neutralized Bags
Even with severe restriction of air to the crystals, they will neutralize eventually, requiring reconstitution:
Place the pouches in a 350º heated oven for several hours*. I use a toaster oven, to limit my electrical bill. Once all the humidity has been baked out of the crystals, they are ready to work again.
If you don’t have an immediate use for them, place them in small canning jars, barely big enough to fit (again, the idea is to limit exposure to air), until ready to deploy.
* Make sure that the silica pouches are of the type that can be reconstituted. Some small ones are one-time only (the tiny ones you find in pill boxes and camera cases). The larger, rechargeable ones usually have instructions on the pouch how to re-dry them.