Neutrons axe the big questions of ancient bronze hoard

15 January 2019

In the latter stages of the Bronze Age, people in Europe started to do something rather strange: they gathered together vast quantities of valuable objects and buried them in the ground – seemingly with no intention of ever coming back for them. Nearly 3,000 years later some of these enigmatic objects, a hoard of axe heads, are being examined at ISIS Neutron and Muon Source in the hope they will surrender some of their secrets.

Huge quantities of bronze, often amounting to tonnes, were buried in isolated hoards during the final stages of prehistory, mainly at the end of the Bronze Age. Despite decades of archaeological investigation and scientific discussion, we still don’t understand what motivated so many disparate committees of ancient peoples to express themselves in this way.

The practice of burying high-value objects like axes and everyday utensils was not limited to the late Bronze Age – it had been taking place for centuries during the Bronze Age and continued well into the Iron Age – but the frequency and quantity of burials peaked between 1000 and 800 BCE. It was once thought the hoards represented an attempt to store and secure tools and weapons for future use, but in many cases the objects were deliberately bent, broken or otherwise ‘decommissioned’ as if to prevent people digging them up and using them. This has led many to conclude that the hoards may have a religious, or ritualistic intent – perhaps as offerings to the gods.

This idea seems to be backed up by the fact that in some hoards, rather than finding once-functional but now decommissioned tools, archaeologists have unearthed tools that seem to have been manufactured to function purely as ritualistic objects. These objects resemble the tools they are meant to represent, but have either been poorly cast and left incomplete, or have been manufactured in such a way that they would never be any use as functional items.

In 1849 one hoard of bronze axe heads was discovered in Spain that might fit into this latter category. These axes, which superficially resemble functional bronze axe heads, have been found to contain large quantities of lead, which as a metal is too soft to be of use in a blade intended for cutting. More curiously still, one of the axes that had been broken in half, was found to have a core of pure lead covered by only a superficial casting of bronze.

Now a museum collaboration is using ISIS Neutron and Muon Source to investigate ten of these axe heads to see whether, as they suspect, all of the axes were manufactured in this manner. The collaboration is between University of Rome Tor Vergata, UCL Institute of Archaeology and the British Museum (which is home to the samples). The team hope to learn what manufacturing technologies were used to make the axe heads as well as reveal their internal structure. A neutron source like ISIS is ideal for this kind of investigation because neutrons can pass through dense materials such as metals – allowing them to be studied in a non-destructive and non-invasive manner.

They also hope that the investigation will tell them where the lead came from and perhaps give clues as to why it was used in the first place. If the axes were intended as purely ritualistic objects, why go to the effort (and expense) of using lead to ensure the axe heads had the same weight and physical characteristics of pure bronze?

The investigation of the axe heads’ internal structure has already taken place using ISIS’s IMAT beam line and the team will be returning in July to perform a chemical analysis of the samples.

Last updated: 25 February 2019


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