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A complete plano-convex ingot has been found in Sweden for the first time. The results of the isotopic and chemical analyses carried out by archaeologists at the University of Gothenburg are in the Journal of Archaeological Science: Reports.

Plano-convex ingots are often made of copper, but can also be made of bronze or copper-based alloys. These ingots are a common find, especially in the Mediterranean, but also in continental Europe and along the Atlantic coast. They were used to transport metal throughout the Bronze and Iron Ages.

Initially, the archaeologists at the University of Gothenburg believed the Särdal ingot to date back to the Bronze Age. However, as it was found alone and could not be dated by its archaeological context, they decided to run isotopic and chemical analyses to determine its composition and suggest a possible chronology.

"Due, in particular, to its shape and size, it seemed to us a Bronze Age artifact, but the ingot turned out to be made of a copper-zinc-tin-lead alloy, typical of the Iron Age and later periods," says Serena Sabatini.

"Thanks to the collaborative climate of the archaeometallurgy research world, we teamed up with a group of Polish scholars, who were working with some Iron Age finds that have the almost exact composition of our ingot."

The results show that unique, isolated finds, which are traditionally considered very difficult to interpret, can be given historical context and contribute to our understanding of the past when carefully analyzed through an interdisciplinary approach that includes both archaeological and natural science methods.

"Networking and international collaboration are also important to unveil patterns and data that would remain unknown when one looks exclusively at the local context. This work clearly shows the importance of teamwork and data sharing. Without the successful collaboration with our Polish colleagues, we would never have achieved such remarkable results," says Sabatini.

The study uses well-established analytical methods in archaeometallurgy (which is the branch of archaeology specialized in the study of ancient metals), such as lead isotope and trace element analyses of metal finds. Such methods have been used since the 1980s to investigate the composition and the origin of the metal (in the sense that they enable identification of the mineral region from which the metal was extracted).

"What is new in this study is that we went a step further, and by combining the obtained data with known historical and archaeological information, we managed to propose a historical context, for both the unique Särdal plano-convex ingot and the rod ingots from the Iława Lakeland area in northeastern Poland.

"Given the astonishing similarity of the metal composition in all those artifacts, we also managed to strengthen earlier hypotheses about contacts and networking in the Baltic area during the Nordic pre-Roman Iron Age," says Sabatini.