The painting known as the Mona Lisa has been in the Grand Gallery of the Louvre since 1804, where it remains the preeminent attraction. Its fame has necessitated special signs, carefully arranged locations and other precautions. The painting, on poplar panel, is encased in a 157x98-inch box of Triplex glass (a gift from Japan). The virtually bulletproof glass box maintains a constant temperature of 68°F and 55% relative humidity through a built-in air conditioner and nine pounds of silica gel. It also has a built-in alarm system which is dismantled once a year during an environmental check. The curator notes that the paint film is in good condition except for discolored varnish and a damage on the left elbow of the subject caused by a hurled stone in 1956.