In texts predating the Han, "metal" most often meant bronze. "Auspicious Bronze" signified bronze of the fines…
In texts predating the Han, "metal" most often meant bronze. "Auspicious Bronze" signified bronze of the finest casting. When Mozi speaks of Yu the Great "gathering metal" to forge the Nine Tripods, it evokes miners cutting copper from the mountains and founders coaxing sacred vessels from molten alloy.