Period: Viking Age (c. 750- c. 1070 AD)

Project title: Överfångssgjutning på silver och järn- experimentell metodsstudie

Researchers: Ander Söderberg, Ny Björn Gustafsson and Erika Åberg, Järnkontorets kommitté, Stockhom, Sweden

E-mail: a.soderberg(at)chello.se

Year: 2006

Abstract:

Casting-on technology - i.e. the art of casting non-ferrous details onto metallic objects - sometimes occur among Scandinavian Viking artefacts. The aim of this project was to study the technique itself, instead of concentrating on the artefacts. The starting point was a group of Gotlandic arm rings, consisting of a number of twisted silver rods fixed to each other by means of two silver dragonheads cast on to the ends of the rods.

During a week all stages of the casting was experimentally performed in a charcoal-fuelled pit furnace blown with hand bellows. The study included preparing silver rods, mould making and finally the casting itself.

The use of fluxing agents is a crucial factor when casting onto metallic surfaces. Without such agents the molten metal will not fuse with the heated and oxidized solid metal. In the casting experiments, three fluxing agents were tested – borax, pine resin and a mixture of table salt and burnt argol (wine stone, potassium bitartrate), of which resin and wine stone were readily available in the late Iron Age and early Middle Ages. When it comes to medieval availability of borax, archaeology cannot tell, but a satisfying result from the experiments is that use of argol/wine stone that was recommended already in the 12th century manuscripts, seem to work just as well. The experimentally produced pieces will serve as references in further studies of medieval cast-on objects.

Reference number: HAF 13/06