Unique copper alloy ingot found in Sweden

A copper alloy ingot from the from the Scandinavian pre-Roman Iron Age that emerged from Särdal on the west coast of Sweden, in 2022 is the first of its kind ever found in Sweden. An analysis of its composition has found it is also a metallurgic twin to metal hoards from the same period found in Poland.

It was actually discovered almost 50 years ago by the Pedersen family when they were digging a fence post hole in their garden. No other objects were found with it or in the immediate area. They didn’t recognize it as a prehistoric artifact and stored it in their workshop for night on five decades until a friend of the family who was an amateur historian suggested that they show it to archaeologists at the Halland Museum of Cultural History.

It is a plano-convex ingot, a disc-shaped artifact with a flat topside and curved underside manufactured by open casting into a shallow mould or cavity in the ground. Also known as bun ingots or casting cakes, the pog-shaped ingots have been found across the Mediterranean area and continental Europe, with numerous examples found on Bronze Age and Iron Age shipwrecks.

Studies have shown that even though Scandinavia is rich in copper ore, it was not mined in the Bronze Age. Instead, all copper was imported from as far away as southern Europe, and the volume of trade was enormous. Researchers estimate that literal tons of foreign copper were imported into Scandinavia each year going back as far as the 3rd and 2nd millennium B.C. As essential raw materials, ingots are an important source of information about how metal was sourced and traded from the Bronze Age and later into the pre-Roman and Roman Iron Age.

Lead isotope and elemental analysis of copper alloy archaeological artifacts can pinpoint the geographic origin and chronology of the ore. The Särdal ingot emerged just as researchers at the University of Gothenburg. were running a new investigation into Bronze Age metal use in western Sweden, and since the plano-convex shape and dimensions of the ingot were typical of Bronze Age pieces, they incorporated this unique find into their study.

Much to their surprise, the analyses revealed that the ingot was of much later date, composed of copper-zinc-tin-lead alloy typical of the Iron Age. Information sharing with Polish archaeometallurgy researchers led to another surprise discovery: the Särdal ingot shared almost the exact same metallurgic composition two hoards of metal rods found in Poland between 2013 and 2015.

The source of the copper for all of the objects in the study, including the Särdal ingot and Polish rod ingots, were the zinc-rich copper ores occur of southwest Spain.

Iberian copper becomes a dominant ore source for Scandinavia already during the Late Bronze Age. Data from the subsequent Iron Age are not abundant, but the Iberian mines are intensely exploited during this period as well […]. Additionally, the quaternary alloys individuated in all the studied material is increasingly common in the Mediterranean since the 1st millennium BCE […], largely replacing the Bronze Age typical binary copper-tin alloy. Studies from the Baltic regions, which were intensely networking with West Sweden and southern Scandinavia during the pre-Roman Iron Age […], indicate that Cu-Sn-Zn-Pb alloy of the type from Särdal and the Iława Lakeland was present in the area already during the second half of the 1st millennium BCE […]. We propose therefore that the plano-convex ingot from Halland and the rod ingots from Poland can be both considered the outcome of maritime trade in metal connecting Scandinavia and the Baltic Sea to the Iberian Peninsula during the period corresponding to the Scandinavian pre-Roman Iron Age, following ancient routes in use since the Late Bronze Age.

* This article was originally published here