cleaning bronze

Ketchup will clean it safely, you might have to give it a couple hours to work, and loosen the oxidation with a soft brush, rinse thoroughly and dry. It will be nice and shiny, but it will immediately start to oxidize again. Metal polishes like Flitz will protect it but not for long. It is hard to seal bronze because whatever you use won't adhere well to the metal, and out in the elements it will chip and flake and then it will look really bad.