II.

Types

Tin bronzes, the original bronzes, are alloys of copper and tin. They may contain from 5 to 22 percent tin. When a tin bronze contains at least 10 percent tin, the alloy is hard and has a low melting point. Leaded tin bronzes, used for casting, contain 5 to 10 percent tin, 1.5 to 25 percent lead, and 0 to 4.5 percent zinc. Manganese bronze contains 39 percent zinc, 1 percent tin, and 0.5 to 4 percent manganese. Aluminum bronze contains 5 to 10 percent aluminum. Silicon bronze contains 1.5 to 3 percent silicon.

Bronze is made by heating and mixing the molten metal constituents. When the molten mixture is poured into a mold and begins to harden, the bronze expands and fills the entire mold. Once the bronze has cooled, it shrinks slightly and can easily be removed from the mold.