Most blue zircon sold in jewelry today is produced by heat treating brown zircon in a reducing atmosphere to 900 to 1000 degrees Celsius. Some people have damaged these blue zircons by exposing them to ultraviolet radiation in tanning beds or under ultraviolet lamps used to cure acrylic fingernail adhesives. The blue color can degrade to brown with just minutes of exposure. The color of some of these gems have been restored by exposure to low wattage incandescent light. To avoid ruining a nice gem, remove jewelry at tanning and nail salons.