I once read that the frames were the same "bronze" as used in cannon barrels. If so, it would have been 90% copper & 10% tin. Also one of the reasons the bronze church bells were removed and melted in the name of patriotism, especially in areas with gun factories throughout the south. Not 100% about this mix, copied it down from a source years ago. Zonie's much more knowledgeable than I ever hope to be along these lines, perhaps he(or others) will jump in and correct this if wrong! :thumbsup: