I use a boat fiberglass hull cleaner. It does a nice job getting the surface clean and removing fine scratches. OhioBeeFarmer Getting Kids Involved in 4H Beekeeping www.homestead.com/BeeKeepers/ www.homestead.com/BeeKeepers/BeesRUs.html Subject: [BEE-L] cleaning observation hive Something that won't damage the plexi-glass or hurt the bees.