Q: "We have 20-year-old genuine alabaster sconces that have a discolored spot on the outside of the alabaster ‘lenses’. Can this be safely removed?"
A: This situation occurs quite often. What usually happens is people put in higher-wattage bulbs than what is recommended for the fixtures, and the alabaster closest to the bulbs gets "cooked." In your case, the heat shield was removed or lost, and the unshielded heat from the 60W bulb caused the discoloration. More...