Alloys of copper and either arsenic or tin were so widespread and important from around 6,000 years ago the period has been named the Bronze Age. Yet the purpose of daggers widely found in graves from the era has been unknown in the face of questions about their functionality. New evidence indicates they were used for processing animal carcasses, rather than being purely status symbols, as previously suspected.

Bronze Age graves are loaded with daggers, presumably to mark the significance of the person buried there. These appear about 6,000 years ago across central Europe, indicting the technology spread very rapidly, and subsequently dispersed across all of Europe. However, archaeologists were frustrated by an inability to establish if these blades were purely symbolic, or if they had practical uses. Techniques used to test other materials of the day, such as ceramics and stone, for residues don't work for copper alloys.

For Professor Andrea Dolfini of Newcastle University that created a challenge to develop a new approach to find out. In Scientific Reports, Dolfini and co-authors announce their success, and the results of applying their technique to 10 daggers dug up from Pragatto, Italy in 2017. The daggers were buried some time between 1550 and1250 BCE just as the Bronze Age was drawing to a close.

The authors stained residues on the blades with Picro-Sirius Red (PSR) solution and then examined the product under optical, digital and scanning electron microscopes. Combining the different information these microscopes provided the team found residues indicative of having been used to cut animal tissues, including bone, muscle, tendons and collagen.

The authors suspected the daggers were used to kill livestock and butcher their carcasses, including carving meat from the bone. They tested this hypothesis using replicas made by a modern bronzesmith, demonstrating the daggers were well-suited to the role, contradicting previous claims the design and composition of daggers like these made them suitable for symbolic uses only.

It's not always easy to distinguish human residues from those of other large mammals and the paper acknowledges, “Daggers may have had additional uses, e.g., as close-range weapons.” Nevertheless, cutting up animals for food or hides was probably a lot more common than murdering enemies.

Over thousands of years bacteria will usually break down animal tissue, but in certain cases the combination of salt and metal prevents this from happening, allowing the animal residue to survive.

The earliest copper-alloy daggers have counterparts made from flint in similar graves from the same region and era. However, as time went on flint daggers appear to have been the Betamax of the Bronze Age, left behind by copper alloys' popularity.

“The research has revealed that it is possible to extract and characterize organic residues from ancient metals, extending the range of materials that can be analyzed in this way,” Dolfini said in a statement. “This is a significant breakthrough as the new method enables the analysis of a wide variety of copper-alloy tools and weapons from anywhere in the world. The possibilities are endless, and so are the answers that the new method can and will provide in the future."