Analysis of copper-alloy artefacts from the Viking Age

Abstract

Viking Age copper-alloy artefacts from Uppland (south central Sweden) were analysed by SEM/EDX to concretise differences in metal composition. Arte-facts were selected from two settlements (Birka and Rasbo), and four ceme-teries: Birka, Lovö, Norrsunda/Valsta, and Sollentuna/Häggvik, all within a limited area and with social and economic contacts with the world around. The analyses of the Viking Age finds reveal large variations in metal com-position, and large differences compared with Bronze Age artefacts. Few objects were made of “conventional” bronze with 5–10% tin. Instead, tin was often replaced by metals such as zinc, lead, and iron. We attribute this significant change to gradual innovations in mining and metallurgy on the continent. Arte facts of almost pure copper were also found. Seventeen gilded oval brooches from Birka graves form a homogenous group with respect to type, dating, and a high copper content. The artefacts’ preservation was also examined in order to find possible connections to the composition of alloys. The most corroded finds were those from Birka, with corrosion of metal oxides, carbonates, chlorides and sulphates, an effect of polluted soil. No particular alloy could be singled out as being particularly corrosive.