One of the most effective moisture absorbers ever developed. These man-made crystals prevent rust, mildew, corrosion, and tarnish before they start by literally "sucking up" and safely holding the moisture that causes them. Yet, the crystals stay dry to the touch, will not harm or dampen any surface even when saturated. When built-in indicator changes from blue to pink, the crystals have all the moisture they can hold, and are easily reactivated by heating in a conventional oven for 3 hours. The crystals can be reactivated over and over again, giving you a lifetime of protection from the destructive effect of dampness. Gives longest time between reactivations when used in enclosed areas and containers. Perfect for tool chests and lockers, closets, safes, etc., to protect guns, cameras, silver, clothing, documents, leather, medicines, electronics and tools. Several boxes may be used together for large gun cabinets and chests, closets, darkrooms, boat lockers.