Tuesday, January 8, 2019

Metallurgy in the Americas – Part II

Continued from the previous post regarding the presence of metallurgy in South America, where archaeologists claim metallurgy began, and from there traveled northward into Central, Meso-, and North America. It was also discussed that archaeologists have a way of tracking ancient metalwork through the by-products of smelting that are left behind, such as slag and till.
The closed mine today at Cerro Ricco de Potosí shows the original stone work around the opening where enormous amounts of silver were extracted

These by-products are left behind at the site rather than being moved away with the product. It also weathers well and therefore readily available for study. The size, shape, chemical composition and microstructure of slag are determined by features of the processes used at the time of its formation.
    According to Gray Graffam, additional evidence for early smelting to the southwest comes from recent research at the Ramaditas site in the Guatacondo Valley of northern Chile, where excavations have revealed evidence that copper smelting and sheet metal working (repoussé) began near the first century BC. This finding confirmed that not only does metallurgy date back in excess of 2,000 years in northern Chile, but that this activity was often carried out independent of the presence of a large formalized state or Empire (Graffam et al., “Ancient Metallurgy in the Atacama: Evidence for Copper Smelting during Chile’s Early Ceramic Period,” Latin American Antiquity, vol.7, Iss.2, 1996, pp101-113). In fact, investigations at the Ramaditas site in Guatacondo Valley of northern Chile, discovered small quantities of ancient metallurgical slag, copper ore, and metal from sealed archaeological contexts dating to the first centuries BC. This is partly because Northern Chile contains abundant ores of copper and the exceptionally arid environment allows excellent preservation of artifacts, which makes Chile an ideal locality to conduct metallurgical research.
    Such results are significant since they show that copper smelting and metal manufacture were taking place in the Atacama in antiquity, establishing the first conclusive proof of what many Chilean scholars have believed since the early 1970s. These results support the view that the mining of minerals and the winning (leaching) of metals played a valuable role in the economy of the first sedentary villages of interior Chile, in the foothills and valleys that rim the Atacama Desert in late BC times.
Cerro Ricco, in Potosí, Bolivia, near Lake Titicaca, where silver has been mined for millennia

In addition, along the Andean Altiplano, a silver deposit known as Cerro Ricco de Potosí was once the world’s richest silver mine. While some modern historians attribute this to the penultimate (next to last) Inca ruler, Huayna Capac, this was recently challenged by the discovery of much earlier metal pollution in a nearby lake that can only be explained by local smelting activity.
    It is interesting that John L. Sorenson, in defending why no such physical evidence of metallurgy has never been found in Mesoamerica before about 900 AD, suggests that someday, perhaps, it will be.
    The problem with this is that, as mentioned above, slag and till are not moved away—anciently, they had no value for anything and to move the large quantities of heavy slag would have been meaningless. It should be noted, that while these slag heaps have been found in Andean South America, no such evidence has been found in Central or Mesoamerica until much later than Nephite times.
    The importance of finding such slag evidence is because the ores used in ancient smelting processes were rarely pure metal compounds. Impurities were removed from the ore through the process of slagging, with the material in which the impurities from ores (known as gangue, which even today is commercially worthless), as well as furnace residue and charcoal ash, collect at the site. This makes the study of slag important because it can reveal information about the ancient smelting process used at the time of its formation.
    In addition to the slag and till and other residue at the site, another way to evidence ancient metallurgy is finding trace metals, which during smelting, are released into the atmosphere. These subsequently become deposited into surrounding areas, including lake environments through precipitation and dry atmospheric deposition.
The accumulation of metal deposition within the lake bed sediment

As soils, algae, and sediments accumulate at the bottom of a lake, they preserve these atmospherically derived metals. According to Ingemar Renberg natural archives, such as lake sediments, are sensitive enough to pick up even preindustrial emissions (Renberg, et al., “Sediment Evidence of Early Eutrophication and Heavy Metal Pollution,” Journal of the human Environment, vol.30, iss.8, AMBIO, Stockholm, Sweden, 2002, pp496-502).
    These lake sediment cores (tubes of sediment recovered vertically from the bottom of a lake) were collected from a high alpine lake downwind of Cerro Ricco de Potosí. Geochemical analysis of the sediments revealed a long history of smelting activity hundreds of years prior to the supposed discovery of silver! The use of this method to track metallurgical activity has only just begun and research is currently underway to understand the chronology of smelting throughout the Andes.
    The final source of information on indigenous smelting comes from a combination of historical archives and ethnoarchaeological (study of peoples for archaeological reasons, such as material remains of a society) research. Given its richness, Potosí was the central focus of colonial mining for years after conquest. As a result of this attention, a written chronicle of smelting techniques in use at Potosí exists. For example, silversmiths under colonial rule using indigenous furnaces conducted all silver production. 
    Three different types of furnaces were recorded by the Spanish when they arrived—the first type was simply a pit dug into the ground that reduced ores rich in silver; the second type was a small, and sometimes portable, reduction furnace called a huayara, which were often placed on mountaintops to take advantage of strong winds to drive the charcoal-fired, wind-drafted furnaces, which were lined with clay. Unfortunately, they were prone to destruction by any number of natural forces such as landslides, earthquakes, severe storms, etc., and to date none have been recognized in the archaeological record. However, according to Mary Van Buren, a huayara has been found today still in use in western Bolivia. This is an important discovery, which promises to contribute a great deal toward the understanding of ancient smelting techniques and their remains in the archaeological record.
Crucible fragment containing silver-rich slag, excavated from a pre-Columbian workshop by Lake Titicaca

Because native silver is a rare element, although it does exists as such, it is usually found in nature combined with other metals, or in minerals that contain silver compounds, generally in the form of sulfides such as galena (lead sulfide) or cerussite (lead carbonate). So the primary production of silver requires the smelting and then cupellation of argentiferous, or lead ores containing silver.
    The refining process of cupellation in metallurgy, where ores or alloyed metals are treated under very high temperatures and have controlled operations to separate noble metals, like gold and silver, from base metals like lead, copper, zinc, arsenic, antimony or bismuth, present in the ore, have been found at ancient sites in southern Peru and western Bolivia, especially around Lake Titicaca. This extraction was especially important in making bronze with the process to obtain silver from smelted ores.
(See the next post, “Metallurgy in the Americas – Part III,” for more on this subject and how Andean South America is the only area in the Americas that shows metallurgy, in addition to just copper, being practiced at a time of both the Jaredites and the Nephites)

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