I recommend using a 50/50 Propylene Glycol/distilled water solution. Propylene Glycol inhibits microorganisms and automatically regulates at %70 RH. Sacrifice a Spanish cedar cigar box and cut a circle of it for the bottom of the jar. Place it in there unfinshed side up. The wood will help retain moisture and regulate the humi. Your local cigar shop may be able to help supply you with a box. All you need after that is a jigsaw or scroll saw and some sandpaper. Also keep the jar out of direct sunlight, and in the dark as much as possible.