Like copper, bronze can develop a patina, a green film as a result of long exposure to moist air. This patina will actually protect your bell from many environmental hazards. However, bronze will deteriorate rapidly if exposed to moisture that contains chlorides or sulfides.
Bronze is susceptible to "bronze disease", one of the most serious hazards of bronze. This disease is caused when chlorides and oxygen combine in a damp environment and then "attack" the metal. The disease can be recognized when a sudden outbreak of small patches of corrosion, rough, light green spots, forms on the bronze piece.
Metal care tips for bronze
Bronze forms a patina (green color) that is protective to the metal and is often seen on artwork. Reproduced, it is called Verde Solid.
Bronze often is lacquered (at the factory) to protect the finish. Lacquered bronze only needs dusting and an occasional wiping with a damp cloth. Have the lacquer replaced if it cracks or peels. Bells are not lacquered, though, as this may negatively affect the sound. It's also simply not necessary in the normal environments where bells would be found.
It's good occasionally to clean your bell, although this is not necessary. Accumulations of dust and dirt, particularly in urban environments, can eat into the metal surface. Wipe the bell with a soft cloth, but do not rub too vigorously, especially on any protruding parts. If a bronze piece has been neglected for a long time and is covered with grime, thoroughly clean it with a soft brush. Remove all dust from crevices and notches and then lightly rub the entire surface with a soft flannel cloth. For a more thorough cleaning, carefully wash with a solution of 1 tablespoon of salt mixed in to 3 quarts of water. Rinse well.
Wash the piece in repeated changes of boiling hot, distilled water, usually can stop "Bronze Disease". You may have to soak the object for a week or more in distilled water. If this treatment does not work, consult a museum expert about using a strong solution of sodium sesqui-carbonate or have your piece treated by a professional.
A good household general-purpose bronze cleaner can be created. Use salt, vinegar, and flour. Dissolve 1teaspoon of salt into 1 cup of white vinegar. Add enough flour to make a paste. Apply the paste to the bronze and let sit for 15 minutes to 1 hour. Rinse with clean, warm water, and polish dry.
Polish with copper polish followed by glass wax. If a high polish is required dip a cloth into liquid wax and apply to the piece. When the piece is dry, buff lightly to a high gloss. This wax treatment also may be given to bronze pieces that are kept outdoors. Weathered bronze usually darkens; however, this is natural and does not harm the piece
What not to do
Do not use heavy abrasives to clean bronze, or most metal pieces. Do not try to remove the patina.