I've always been a die-hard user of coasters when setting a drink down on virtually any type of surface. However, the other day a friend of mine put his glass down on a wood coffee table of mine without using a coaster and it left a ring in the shape of the bottom of the glass. I tried just wiping it off w/ a paper towel but no luck. Anyone have any suggestions so I don't have to refinish the entire table top? Thanks guys!