White rings, caused when water vapor penetrates into a finish, can be removed by wiping them gently with a cloth barely dampened with denatured alcohol. (Black rings indicate damaged wood and require complete removal of the surrounding finish before any repair can be attempted.) Too much alcohol can dull the finish. If that happens, restore a satin sheen by rubbing with extra-fine 0000 steel wool and paste wax. To bring back a gloss finish, use auto polishing compound applied with a rag. To make the repair blend in, go over the damaged area and the entire adjacent surface.