page_title: Mississippian copper plates
section_title: Methods of manufacture
hierarchical_section_title: Mississippian copper plates / Methods of manufacture
caption_attribution_description: English: A map showing the geographic distribution of avian themed repoussé copper plates, a Mississippian culture elite status goods found as artifacts in the US midwest and southeast.
context_page_description: Mississippian copper plates, or plaques, are plain and repousséd plates of beaten copper crafted by peoples of the various regional expressions of the Mississippian culture between 800 and 1600 CE. They have been found as artifacts in archaeological sites in the American Midwest and Southeast. The plates, found as far afield as Florida, Georgia, Illinois, Mississippi, Oklahoma, Tennessee, and Wisconsin, were instrumental in the development of the archaeological concept known as the Southeastern Ceremonial Complex. Some of the more notable examples are representations of raptorial birds and avian-themed dancing warriors.
context_section_description: The native copper, as well as the technique of cold working it, is believed to have come from the Great Lakes area, hundreds of miles to the north of the Cahokia polity and most other Mississippian culture sites, although the copper workshops discovered near Mound 34 at Cahokia are so far the only copper workshops found at a Mississippian culture archaeological site. Researchers at Northwestern's School of Engineering and Applied Science used an electron microscope to analyze pieces of the flat copper sheets found during excavations at the Mound 34 site at Cahokia. The researchers found that the metal had been repeatedly heated and cooled and while it was softened by the heat, had been hammered, a process known as annealing, similar to how blacksmiths work iron. They were also able to determine that the Cahokian coppersmiths had heated the copper in a wood fire to produce sufficient heat for this process. This process of heating and hammering was repeated over and over until a sheet of the desired thickness was obtained and was sufficient a method to allow the craftsman to work the copper into very thin sheets. Researchers have also tried different techniques to duplicate how larger pieces were manufactured. They determined that the larger pieces had not been laminated together but had most likely been riveted together with small copper knobs. Researchers were also able to determine that the artisans cut the copper into the desired shapes by bending the sheet metal back and forth until it broke in the desired location.
  After the flat sheets of copper were produced, designs were then embossed into the surfaces probably with stone, bone or wooden tools. Frank Hamilton Cushing, an anthropologist working in the early 20th century, worked out a method for flattening and embossing the plates. He hammered raw nuggets of copper smooth and removed imperfections by scouring the surface with a piece of sandstone. He was then able to duplicate the avian designs by resting the sheet of copper on a rawhide pad and pressing into the surface using a piece of pointed deer antler and pressing with his chest. This produced a sharp thin line that when the plate was reversed resembled the embossed lines of the aboriginal artifacts. This process is considered to be roughly similar to how Mississippian coppersmiths probably worked.
caption: Distribution of avian themed copper plates
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