In 1999, an ancient bronze disc with golden patterns was found by chance in Nebra, Germany. Known today as the Nebra Sky Disc, it is 12 inches (30 cm) wide and more than 3,600 years old. Experts believe it is the oldest known image of the night sky.
The disc has been studied for years and is listed in UNESCO’s “Memory of the World” register. A new study reveals more about how it was made. Scientists found that the disc was created using a complex process. The study was published in the journal Scientific Reports.
Nebra Sky Disc could not be simply cast in its final size
In 2002, the Nebra Sky Disc was seized by police from a dealer in Cologne and returned to Saxony-Anhalt, where it has undergone thorough scientific study ever since.
Researchers determined that the disc could not have been created by simply pouring molten bronze into a mold. Its construction required much more effort. Despite its modest look, crafting a bronze disc 31 centimeters wide and just a few millimeters thick was a highly skilled and complex process.
The study was a collaborative effort led by the State Office for Heritage Management and Archaeology Saxony-Anhalt, working with Otto von Guericke University Magdeburg and DeltaSigma Analytics GmbH. Experts used advanced metallographic tools to examine the Nebra Sky Disc.
A small sample from the disc’s outer edge, originally taken in 2002 and later restored, was removed again for further analysis. Scientists applied cutting-edge methods, including light microscopy on specially treated surfaces, X-ray spectroscopy, and electron backscatter diffraction.
Researchers also conducted hardness tests on the Nebra Sky Disc. Alongside these measurements, experimental trials were carried out. Herbert Bauer, an experienced coppersmith from Halle (Saale), recreated the disc using a cast bronze blank.
Ten cycles of heating metal to 700°C to get its final size
The metallographic analysis confirmed that the Nebra Sky Disc was crafted using a sophisticated hot-forging process. Achieving its final size required about ten cycles of heating the metal to 700°C, shaping it through forging, and then annealing to stabilize its structure.
In his experimental work, coppersmith H. Bauer needed more forging cycles to replicate the disc. This suggests that the original bronze blank used for the Sky Disc was likely larger and thinner than the one he used for the replica.
“That the investigations continue to produce such fundamental new findings more than 20 years after the Sky Disc was secured not only once again demonstrates the extraordinary character of this find of the century, but also how highly developed the art of metal processing was already in the Early Bronze Age,” says State archaeologist Prof. Dr. Harald Meller.
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