Wednesday, January 9, 2019

Metallurgy in the Americas – Part III

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 Andean metallurgists used alloys almost exclusively to mold their images.
    The third type of furnace was a tocochimpu, which was normally used to refine silver in combination with argentiferous galena or soroche (lead sulphide). Cieza de León was one of the first Spanish chroniclers to describe the use of soroche at Potosí and documented its use as a flux to enable extraction of silver from even low-grade ores. Future research combining historical archives, archaeological and ethnoarchaeological research is sure to illuminate lingering questions regarding the spatial and temporal homogeneity of smelting technology in the southern Andes. (Colin A. Cook, et al., “Metallurgy in Southern South America,” Louisiana State University, Baton Rouge, 1994, p1660).
    We need to keep in mind that metallurgical activities have been undertaken in northern South America for millennia. In particular, copper extraction and smelting started in northwestern South America as well as northern Chile around 1400 BC and spread with the various South American civilizations, such as Chavin, Nazca, Tiwanaku, etc. (François De Vleeschouwer , et. al., “Emissions from Pre-Hispanic Metallurgy in the South American Atmosphere, PloS One, vol.9, iss.10, San Francisco, CA, Oct 2014).
Tin oxide mineral (black) which has been the chief tin ore throughout ancient history and the most important source of tin today, within a matrix of quartz—the gangue

Perhaps to better understand why all of this was necessary to the ancients, it would be helpful to know what is involved in separating the wanted ore from the gangue or unwanted rock. This separation of mineral from gangue is known today as mineral processing, mineral dressing, or ore dressing, and is a necessary, and often significant, aspect of mining ore. It can be a rather simple process or a complicated one, depending on the nature of the minerals involved. For example, galena, an ore of lead, is usually found in large pieces within its gangue, so does not normally need extensive processing to remove it; but cassiterite, the chief ore of tin, which has been mined for thousands of years, is usually disseminated as very small crystals throughout its gangue, so when it is mined from hard rock, the ore-bearing rock first needs to be crushed very finely, and then has to be subjected to sophisticated processes to separate the ore. This was first done in Ur of Southern Mesopotamia, the home of Abraham, since tin (10%) was used to alloy with copper (90%) to form bronze; besides the tin belt of China, Thailand and Indonesia, tin was also mined in ancient Peru and Bolivia.
    Obviously, the ease with which the ore can be separated also plays an important part in what is mined. Ancient mining, with their relatively unsophisticated methods, often could not achieve a high degree of separation, so significant quantities of minerals found their way into the the slag or waste mineral dumps. In modern times, the slag, when identified, was sometimes re-mined through the use of new and cheaper means of processing the gangue to extract the ore were introduced.
    In terms of archaeology, despite advances in the smelting of ores over the centuries and millennia, direct analysis of the metal artifacts themselves is the most common analytical approach. The most frequent analysis performed is that of a compositional analysis which determines the relative proportions of the metals which make up an artifact. This has shown that the vast majority of Andean artifacts are composed of alloys, and rather than pure metals, have been pervasive in both Old and New World metallurgy for three reasons. First, occurrences of pure copper, silver, and gold do not commonly occur in any large quantity. Second, alloys have the benefit of often being harder than objects made of native metal, as is the case with silver and gold. Third, by combining one or more metals, the melting temperature of those metals is lowered, which facilitates the smelting of ores. This is important as all pre-Columbian metallurgy was generally accomplished without the use of bellows and had to rely on natural drafts to aerate furnaces.
Arsenical copper contains up to 0.5% arsenic which, at elevated temperatures, imparts higher tensile strength and a reduced tendency to scaling (Copper with a larger percentage of arsenic is called arsenical bronze, which can be work-hardened harder than copper)

The most common alloys found in southern South America have been those of arsenic–copper (arsenic bronze), tin–copper (tin bronze) and ternary or three alloys of copper, arsenic and nickel. There is also evidence that ancient Peruvians alloyed bismuth in bronzes recovered from the site of Machu Picchu, where the 168 artifacts collected by Hiram Bingham in 1912 were examined for evidence that metallurgical artificers worked at this site in pre-Columbian times. Of this total, fifteen artifacts have been identified as metal stock, work in progress, or waste materials from metallurgical processes. It was learned that bronze was made by alloying metallic tin and copper and was cast into both finished objects and stock for subsequent forging. Also, hammering was done with stone tools, but bronze chisels were also in use. Silver-copper alloys were worked, but this material was not held to compositional limits as close as those for bronze. No alloys containing arsenic and relatively little evidence of the use of sheet metal were found (John W. Rutledge and Robert B. Gordon, “The Work of Metallurgical Artificers at Machu Picchu, Peru,” American Antiquity, Vol.52, iss.3, 1987, pp578-594).
    Which brings us to the ancient technique of alloying metals. This was necessary early on since pure metals are not as strong as needed, as in the case of pure copper, which was not strong enough to make into weapons anciently, so early metallurgists found that mixing two or more metals or elements together added strength. Thus, a small amount of tin, which alone is a brittle metal, when added to copper, developed a stronger product, anciently called bronze. Bronze was a step up from using stone daggers or knives for weapons, since it could be cast into swords, and preceded the use of iron. At the same time, it was found that by adding zinc to copper instead of tin, a product called brass was developed around 1400 BC, which was both resistant to corrosion and to wear. Eventually, not only zinc was added to copper, but in small amounts both lead and tin, to make an even stronger alloy of brass.
    With stronger metals than bronze needed, particularly in weapons, iron swords were developed, being a harder product than bronze, though both could take a good edge for a blade, and both were more likely to bend and deform before breaking—a problem with all early swords. However, since iron (as well as steel later) could have a fuller (a thicker middle portion of the blade running its length, what some have called a blood groove, though it had no such function), the iron blade was stronger and lighter and therefore better in sword to sword combat than bronze.
    Thus, the discovery (undoubtedly through experimentation) of alloying metals eventually led to the development of steel—a product Nephi tells us was the metal of Laban’s sword (1 Nephi 4:9). This product evidently was an accident, since iron requires a high temperature to melt at 2800º F. (Copper 1981º, Gold 1945º, Silver 1761º, Zinc 787º, Lead 621º, tin 449º). This led to heating furnaces as hot as they could in charcoal fires, producing a spongy mas (bloom) that could be hammered (wrought) into shape—these early smiths noticed that when iron was left in the charcoal furnaces longer, it changed, becoming harder and stronger, which increased with repeated heating, folding and again heating of the material as they forged the metal.
    It is claimed that this process occurred for the first time around 500 BC, and that by 400 BC India metalworkers invented a smelting method that happened to bond the perfect amount of carbon to iron. However, it is known that Cyprus craftsmen were producing quench hardened steel knives as early as 1100 BC. Nonetheless, in the ancient world, steel making remained a lengthy and difficult process, and the rare steel items produced would have been highly prized (Mitchell Kosolofski, “When was Steel First Discovered and Utilized by Mankind?” Quora, 2015).
(See the next post, “Metallurgy in the Americas – Part IV,” 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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