Window cleaner can be used, but not recommended by some. White vinegar and water has long been a home remedy for streakless window cleaning which can be put in a spray bottle and used this way. I use dish soap and give them a bath being careful about the clapper connection, and I think this makes them shine. If vinegar or window cleaner is used, make sure it is not applied to the clapper chain. Paper towels that have a lot of fabric in them tend to leave annoying lint. If clapper chains are not silver or silver coated, they do tend to rust, so carefully drying them is a good idea.