The exterior would have been cast bronze and allowed to develop a natural patina. These bells were cast in a fireclay mold that would have been finely porous and left a smooth, matte finish. It would not be able to hold a high polish without additional machining or buffing of the surface bronze to a mirror finish. The interior may have been machined if the bell were tuned. There should never have been paint or any other coating applied to it. If you have removed the paint down to the base metal, that is as far as you should take it. If the remaining material is a paint of some sort, it is safe to apply a good paint remover such as Strip-Ease. If you buff it with a brush, use a bronze wire wheel or brush as this will not scratch the bell to the degree that a steel brush will do. If the base metal has a nice, even brown or greenish patina, I would not polish it any further as the patina is a natural protective coating. Polishing it to a fine luster will require buffing a layer of patina and bronze off of the bell, and if it is left out in the weather, it will quickly redevelop a patina.
Harry Long, MD