Brass than in brass produced by cementation. These may be "natural alloys" manufactured by smelting zinc rich copper ores in redox conditions. Many have similar tin contents to contemporary bronze artefacts and it is possible that some copper-zinc alloys were accidental and perhaps not even distinguished from copper. However the large number of copper-zinc alloys now known suggests that at least some were deliberately manufactured and many have zinc contents of more than 12% wt which would have resulted in a distinctive golden color. By the 8th–7th century BC Assyrian cuneiform tablets mention the exploitation of the "copper of the mountains"
Ampco Metal into the production of aluminium bronze alloys as sand castings, forgings and centrifugal castings. The company was renamed "AMPCO METAL" in 1930, by which time it had built itself a reputation as a reliable producer of high quality alloys. The Second World War strongly increased the demand for copper-based alloys and industrial bronzes, especially in the field of aeronautics. By 1944, manufacturing operations had grown from 100 to 2,500 employees, and every American airplane carried AMPCO METAL parts somewhere in its structure—in its engines, landing gear, propellers or airframe. In the marine environment, AMPCO METAL propellers were manufactured for landing