A circle of corroded bronze, measuring 12 inches (30cm) across, adorned with golden shapes, was unintentionally discovered in 1999 in Nebra, Germany, now famously known as the Nebra Sky Disc. With an age of over 3,600 years, it is widely considered to be the oldest known representation of the cosmos. A new study is currently underway, where metallurgical analysis has revealed that it was crafted using a sophisticated hot-forging process, involving ten cycles of heating up to 700°C!
Hardly any suitable scientific method was omitted to study the Nebra hoard. (© State Office for Heritage Management and Archaeology Saxony-Anhalt)
An Elusive Manufacturing Process
Part of the UNESCO “Memory of the World” register since 2013, the Disc is considered one of the best-researched archaeological objects. The new study, published in the latest edition of the journal Scientific Reports, finally points us in the direction of the elusive manufacturing process.
Based on its material composition and previous research, it seems that the process would be to heat to 700°C over 10 cycles, then forging, and then annealing to relax the metal structure again.
This affirms what was earlier believed based on the material composition, which indicated that the disk couldn’t have been simply cast in its final size. Consider this: a bronze disk with a diameter of around 31 centimeters, a few millimeters thick – forging this during the Bronze Age without any of the modern tools and technologies available to us today was quite an achievement.
“That the investigations continue to produce such fundamental new findings more than 20 years after the Sky Disc was found 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 in a press release.
The Nebra Sky Disc with the marked sample extraction point ((c) (Reproduced with permission by State Office for Heritage management and Archaeology, Saxony-Anhalt—State Museum of Prehistory, photo: J. Lipták, Munich/Nature).
From Disc-Rescue to Crafting
Discovered in 1999 on the Mittelberg hill near Nebra, Germany, Henry Westphal and Mario Renner made this find when illegally treasure-hunting with a metal detector. The total loot included 2 bronze swords, axes, a chisel, and fragments of spiral armbands, sold to a private dealer. The police led a sting operation and recovered the disc in 2002, now on display in the State Museum of Prehistory in Halle, Saxony-Anhalt, Germany.
Archaeologists have placed the disc, with a blue-green patina (probably originally a deep bronze hue), and adorned with gold inlays, to the Únětice culture, emerging at the start of the Central European Bronze Age around 2300 to 1600 BC.
It was likely made over 4 stages, and eventually deposited into the ground in the form of a ritual offering. Previous studies have pointed to how the arrangement of the cosmos indicated its deep relevance to agricultural communities – likely what it alluded to.
“In addition, the Sky Disc shows how important it is to re-examine seemingly well-known finds when new methods become available,” says Dr. Meller.
After its recovery, a small sample was temporarily taken from the outer area of the Disc in 2002 (since re-inserted), and then temporarily removed again for archaeometallurgical research. It was subject to ‘microstructural analyses on color-etched surfaces with a light microscope’, with modern imaging methods used: energy dispersive X-ray spectroscopy, and electron backscatter diffraction – the most modern metallurgical analyses available.
Following this, the disk was subject to hardness measurements and parallel experimental tests.
The renowned coppersmith Herbert Bauer then made a replica from a cast blank, which was actually subject to many more forging cycles to produce the copy; the original cast blank was probably larger and thinner.
“The latest research results make it clear that the early Bronze Age craftsmen were not only outstanding casters, but also mastered complex bronze processing techniques, for example hot forging, at the highest level. With their extensive experience and knowledge, they were not only able to produce numerous axes in series production, but also to forge a workpiece that is unique from today’s perspective, such as the Nebra Sky Disc,” reports the press release.
The research was conducted by the State Office for Heritage Management and Archaeology Saxony-Anhalt in cooperation with the Otto von Guericke University Magdeburg, Chair of Metallic Materials (Prof. Dr. Thorsten Halle), and the company DeltaSigma Analytics GmbH, Magdeburg.
Top image: The Nebra Sky Disc. Source: Juraj Lipták/ State Office for Heritage Management and Archaeology Saxony-Anhalt
By Sahir Pandey
