Still, gold did teach some fundamental principles of metallurgy that would become useful in later times: discovery (finding and recognizing a metal in nature), concentration (in the case of gold, by cold hammering smaller pieces into larger pieces), and shaping (working the metal into a desired form).
It was copper, beginning in about 4000 B.C., that allowed humans to extend the techniques of metallurgy. Smelting, the use of heat to extract metal from ores, may have been discovered accidentally by potters. Kilns are hot enough to form of copper if the malachite and other copper-containing minerals are present during the firing process. Copper is too brittle to be cold hammered, but it could be hot hammered into sheets. Concentrating copper would have required the melting together of smaller pieces. Copper is a relatively soft metal, but it can be cast into tools and weapons. Copper became the starting point for the invention of alloys. This might have been helped out by natural contamination, mistakes (such as confusion caused by the similarity of the flames from copper and arsenic), or scarcity of ores. Whatever the source, it led to the creation of bronze, the metal that ended the Stone Age, in about 3000 B.C.
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