The Nebra Sky Disc – considered the oldest surviving representation of the sky – required around ten hot forging cycles to make, a new study shows. Considering the technology of the day, its makers must have valued the product exceptionally highly to put in so much effort.
The Sky Disc shows what is thought to be the Sun, crescent Moon, and stars inlaid in gold on a bronze disc, as well as a suspected ship and the horizon. It’s not a map – the earliest example of that is thought to have been made a millennium later – so it is unknown whether its purpose was decorative or religious. However, a tight bunching of seven stars is thought to represent the Pleiades, again raising the question of why these are generally described as having seven, when only six are visible to normal eyesight under the darkest skies.
Despite having been intensively studied since 2002, and even put on the UNESCO Memory of the World Register, its manufacturing process has remained uncertain. In the Early Bronze Age, items this large could not be forged in a single attempt, leaving open the question of how it was made.
Archaeologists and professional metalworkers collaborated to analyze the disc. They have published results claiming it was made using around ten cycles, each of which involved heating the disk to temperatures of 700°C (1,300°F).
In an era where vast sheets of metal roll off production lines, a disk around 31 cm (12.5 inches) across and a few millimeters thick might not seem that hard to make. To us, the fine design of the celestial objects seems the more impressive feature. However, at the temperatures available at the time, bronze would not flow sufficiently to make something so thin relative to its width, particularly with the disc’s low tin content.
Previous analysis showed the bronze was forged in a repeated process, starting with a thicker but smaller blank that was then forged into a shape spiraling out from the center. The disc’s center is 4.6 mm (0.2 inches) thick, but this declines to a third of that at the edge.
A small piece of the disc’s rim was collected in 2002 for analysis and then returned afterward. The collaboration sampled the same spot again to study its microstructure using energy-dispersive X-ray spectroscopy and electron backscatter diffraction, as well as testing the hardness of the material.
Coppersmith Herbert Bauer then attempted to replicate the disk from a blank. The analysis proved the original disc must have been made from a flat cast followed by several hot forging cycles, but not how many were required. Bauer found that, using bronze of a similar composition to that of the disc, he needed ten cycles of heating the bronze and beating it so it spread, starting with a 5-kg (11-pound) hammer, before using progressively lighter instruments. The original craftspeople may have done it in slightly fewer cycles, but not by much, the investigators conclude.
Coppersmith Herbert Bauer in the process of replicating the Nebra Sky Disc, although we also want to know how he managed that moustache.
Image Credit: andesamt für Denkmalpflege und Archäologie Sachsen-Anhalt, Juraj Lipták
The true age of the disc is not known with certainty, along with important aspects of the culture that created it. Rather than being collected in the process of a careful archaeological dig, it was looted by unlicensed metal detectorists in 1999, along with weapons and jewelry, and then retrieved by police in 2002 The accompanying items have been estimated to be 3,600 years old.
The conventional view, held by the State Office for Heritage Management and Archaeology Saxony-Anhalt, among others, is that the disc is a few centuries older than that. However, similarities to some later designs have led some researchers to claim it is 1,000 years younger instead.
“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,” said Professor Harald Meller of Saxony-Anhalt-State Museum of Prehistory in a translated statement. Meller led the operation that retrieved the disc from collectors who had bought it illegally. “In addition, the Sky Disc shows how important it is to re-examine seemingly well-known finds when new methods become available.”
The study is published open access in the journal Scientific Reports
Source Link: Oldest Depiction Of The Sky Took Bronze Age Craftspeople Ten Forging Cycles To Create
