A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 2 4 HOOP RING IN THE EL VERGEL TRADITION The El Vergel metalworking tradition (1000 to 1500 A.D.), includes objects such as square notched hoops shown in Fig. 1, flat circular hoops, simple circular hoops, bracelets, and rings. These pieces are characterized by being small in size, not very thick, made up of a single piece, without moving or articulated parts, and without engraved or cut-out and/or relief decorations. All these pieces are made of copper. The type of notched quadrangular ring belonging to the El Vergel metallurgical tradition surely ceased to be manufactured at some point before the 18th century, but may have continued in use as it passed from generation to generation. The quadrangular notched ring (also called “Chawai Chapel”) presents, macroscopically, a good state of conservation and only a gentle cleaning was necessary to begin studies. The chemical composition shows it is composed of copper (94.83%) and arsenic (4.32%), and the rest are trace elements. The data on the copper-arsenic alloy is very interesting and allows this piece to be located on the timeline, because this alloy tends to be the dominant alloy before the 1500s. According to metallographic studies, the simultaneous concurrence of an approximately constant composition and an adequate proportion of arsenic (<8%) results in the typical structure: a solid copper-arsenic solution made up of a single phase[6]. Then, arsenic would have been added with intention or considered a fortuitous event according to the characteristics of the minerals in the region: enargite (CuAsS4) and tenn- antite (Cu3AsS3), and it would also be considered valid. In other words, although they could not know that they “technically” manufactured a copper-arsenic alloy, they could take into account that when processing the enargite they had a metal with better qualities and a more red color than that resulting from the processing of malachite [Cu2 CO3(OH)2]. Themicrohardness test shows that the manufacturing process was by successive reduction of thickness by forging and reheating of the original stem to stretch it both longitudinally and transversely. The average value of microhardness in the longitudinal direction is 154 HV and in the transverse direction it is 150 HV. The microhardness value of a current Cu-As alloy is: 151 HV. The Cu-As alloy improves properties such as resistance, hardness, malleability, and ease of fusion, which indicates the degree of technological development of the Mapuche to achieve a resistant material. BRASS ALLOY CONES A study of brass alloy cones illustrates the change of raw materials used in the region around 1800 A.D., and is attributable to the processes of social and political transformation strongly fueled by the arrival of Europeans and the creation of the border. Both indigenous and Spanish-Creole metal artisans (criollos) would participate in this process, adapting to the aesthetics of both worlds, leading to changes in the universe of the manufactured pieces[7]. The cones (Fig. 2) indicate a process of recycling of materials, their chemical compositions are very uniform and the interesting fact is that brass was introduced in the Southern hemisphere by the conquerors. It is possible that these cones were integrated into pectoral pendants called ‘Sikil’ but made of copper. The ‘Sikil’ made of silver seem to arise after the 19th century, approximately in 1860 A.D.[8]. From the microhardness measurement it is possible to suggest the manufacturing process of the receptacle. It could be that the original ingot had a greater plastic deformation at one of its ends to form a thin sheet, which was laminated in a certain way using, for (a) (b) (c) (d) Fig. 1 — (a) A quadrangular hoop with notch as found in Mendoza, (b) the microstructure, and (c) and (d) chemical composition.
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