Silica gel can be used to remove moisture from the air, or as a humidity-buffering agent to maintain or buffer the relative humidity (RH) to a constant level. In either case, silica gel must be conditioned.
Silica gel comes in two forms: indicating and non-indicating. Both can be dried in a regular oven, not a microwave, at 250˚F (120˚C). The amount of time needed to dry gel can vary, but if spread out in a single layer on a baking sheet, one hour should be a sufficient amount of time to thoroughly dry gel.
The simplest way to condition silica gel to a higher RH is to enclose it in a sealed container or zip lock bag with a source of water—a dish of water or a soaked sponge—making sure it doesn’t come in contact with the water. Leave for one day to equilibrate. To test the RH of silica gel, enclose a sample of the conditioned silica gel in a sealed container or plastic bag with a hygrometer for one day and then take a reading.