Wednesday, March 30, 2011

Metallurgy in pre-Columbian America – Part II

South American metal working developed in the Andean regions of modern Peru and Bolivia with gold being hammered and shaped into intricate objects, long before such workings existed anywhere else in the Americas. While the Great Lakes area or the Eastern United States region, did have precious ores and metals cut in objects, it was with the natural appearance as the metals came out of the ground. Actual metallurgy, that is, the “The science and technology of metals, their extraction from ores, purification and alloying, heat treatment, and working,” was first achieved, and to a very high degree, in the Andean area of South America long before anywhere else in the Western Hemisphere.

Evidence for this type of metal work comes from the sites at Waywaka, Chavin and Kotosh, and it seems to have been spread throughout Andean societies by the Early horizon, that is from the 1000 B.C. to 200 B.C. period.
Ancient Peruvians were interested in gold and precious metals for wealth and status, as the jewelry shown suggests, including using electroplating as in the case of the rings)

Unlike in other metallurgy traditions where metals gain importance due to their widespread use from weaponry to every day utensils, metals in South America (and later in central America) were mainly valued as adornments and objects representative of a high status, though more functional objects were being produced. This was not the case in the eastern U.S., where metal workings were simple and merely functional, with few adornments unearthed, and not in Central America until much later into A.D. times.

It is during the Early Horizon (1000-200 B.C.) that advancements in metal working result in spectacular and characteristically Andean gold objects made by the joining of smaller metal sheets and also with gold-silver alloys. Two traditions seem to have developed along side each other—one in Peru, Bolivia and Chile (Nephites) and one in Ecuador (Jaredites), There is evidence for the earliest smelting of copper in the Altiplano region, Cuzco and Titicaca (Sacsahuaman and Tiwanaku) during the early stages of the Early Horizon period. Evidence for this comes from copper slag recovered at several sites with the ore itself possibly coming from further south.

Evidence for fully developed smelting however only appears with the Moche culture (northern coast, 200 B.C. - 600 A.D.). The ores were being extracted at shallow deposits in the Andean foothill, probably by specialized workers and are believed to have been smelted at nearby locations, evidenced in the actual metal artifacts and from ceramic vessels depicting the process, which is believed to have been occurring in adobe brick furnaces with at least three blow pipes to provide the air flow needed to reach the high temperatures.

The resulting ingots would then have been moved to other centers where shaping of the object would occur in specialized workshops. Both of the workshops found and studied were located near administrative sections of the respective cities, which is indicative of the high value placed upon metal. The objects themselves were still mainly adornments along with functional items that were elaborately decorated and often found within high status burial contexts. For this reason, it is believed that they were still being used more for symbolic purposes and to display wealth and status, since there were a high number of gilded or silvered objects as well as the appearance of Tumbaga—an alloy composed mostly of gold and copper that has a significantly lower melting point than gold or copper alone, yet is harder than copper, while maintaining malleability after being pounded. In addition, arsenic bronze was also being smelted from sulphidic ores.

Tumbaga, first used in the Andean area of South America and later spread to Central America, was widely used by the pre-Columbian cultures, especially to make religious objects. Like most gold alloys, tumbaga was versatile and could be cast, drawn, hammered, gilded, soldered, welded, plated, hardened, annealed, polished, engraved, embossed, and inlaid.

The proportion of gold to copper in artifacts varied widely among the ancient Peruvians, with some unearthed items having as much as 97% gold, while others contained 97% copper. Some tumbaga has also been found composed of metals besides gold and copper, up to 18% of the total mass of the tumbaga. However, tumbaga objects were often made using the lost wax technique, a process perfected in Peru and considered as good or better than any techniques employed in Europe or elsewhere for the period. This lost wax method used an alloy mixture of 80% copper, 15% silver, and 5% gold.

No type of this advance work, which flourished in the Andean area in B.C. times, has been found in any artifacts unearthed in the Great Lakes area or eastern United States. It is unique to South America in B.C. times, and only shows up in Central America in later A.D. In the are of the United States, indigenous cultures did not smelt, melt, or alloy metals relying instead on the relative abundance of native ore.

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