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Archaeometallurgical investigation of the Nebra Sky Disc

The world heritage object Nebra Sky Disc is one of the best investigated archaeological objects. The origin of the raw materials it is made of is well known. However, its manufacturing process was not completely clear. Investigations were made in order to clarify the steps of manufacturing from the initial casting to the finished disc using the latest metallographic techniques. Therefore, a small piece from the outer part of the disc was investigated and compared with a replica. Both were prepared regarding the metallographic procedure. Microstructural analysis was made by optical microscopy on a colour etched surface, EDS and electron backscatter diffraction. For the investigation of mechanical properties microhardness measurements were made. It could be found that the Nebra Sky Disc was manufactured from a flat cast followed by hot forging process. During the forging process the disc was heated and forged for approximately 10 times.

The copper smith (Herbert R. Bauer) producing a replica of the Nebra Sky Disc by helical hammer forging ((c) State Office for Heritage management and Archaeology, Saxony-Anhalt—State Museum of Prehistory, photo: J. Lipták, Munich). While the production of axes and sheet metal jewellery by forging techniques were common practice in the Central European Early Bronze Age 13, 17, 18, 19, 21, the Nebra Sky Disc is, according to current knowledge, unique in its shape, size and volume. In this context, the Nebra Sky Disc documents, that the Únětice culture craftsmen were excellent and innovative copper smiths with extensive experience in sophisticated bronze manufacturing, including casting, forging and heat treatment.

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