Investigating a Moche Cast Copper Artifact for Its Manufacturing Technology
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Investigating a Moche Cast Copper Artifact for Its Manufacturing Technology Aaron Shugar1, Michael Notis2, Dale Newbury3, Nicholas Ritchie4. 1 Art Conservation Department, SUNY Buffalo State, Buffalo, New York, USA. 2 Department of Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania, USA. 3 Materials Measurement Science Division, National Institute of Standards and Technology, Gaithersburg, Maryland, USA 4 Microanalysis Research Group, National Institute of Standards and Technology, Gaithersburg, Maryland, USA ABSTRACT A Moche cast copper alloy object was investigated with focus on three main areas: the alloy composition, the casting technology, and the corrosion process. This complex artifact has thin connective arms between the body and the head, a situation that would be very difficult to cast. The entire artifact was mounted and polished allowing for complete microstructural and microchemical analysis, providing insight into the forming technology. In addition, gigapixel x-ray spectrum imaging was undertaken to explore the alloy composition and the solidification process of the entire sample. This process used four 30 mm2 SDD-EDS detectors to collect the 150 gigabyte file mapping an area of 46 080 × 39 934 pixels. Raman analysis was performed to confirm the corrosion compounds. INTRODUCTION The Moche civilization flourished along the Northern coast of modern day Peru from approximately 100 C.E. to 800 C.E. The culture is named after the type site of Moche located in the Moche valley. The culture evolved out of local polities who developed their own political entity and recognizable materials culture. Their lands extended along the coast from the Huarmey river valley in the south to the Lambayeque river valley in the north, before extending inland (NNW) to the Piura river valley. The Moche are best known for their elaborate ceramic vessels and their ability to work metals, in particular gold. The range of metals used in the region is extensive and have a long history. As early as 1800 B.C.E. in the northern/central coast region copper and gold were worked [1]. By the time the Moche culture was established, a long history of working metals including gold, copper, coppergold alloys, copper-sliver alloys, and tumbaga (depletion gilding copper-gold-silver alloy). The newer alloy worked by the Moche appears to be a copper-arsenic alloy [1]. The introduction of arsenic into the metalwork’s repertoire may be directly linked to better trade networks extending along the coast and over the Andes into Bolivia, Brazil and to the North with Ecuador. The range of fabrication techniques mastered by the Moche includes shaping metals by hammered sheet, casting, and extensive joining techniques including folding, riveting, granulation, and soldering.
The association of gold with the sun, and silver with the moon, in Incan mythology is well known; but the association with, and status of copper is less understood. Pease [2] records, and Urton [3] translates the following: “Vichama asked his father, the Su
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