The origin of the clays of the Roman crucibles from Augusta Raurica (Augst, Switzerland)

The project involved analysing 893 Roman crucibles for non-ferrous alloys from Augus-ta Raurica (Switzerland) using laboratory and portable devices. This resulted in the identification of 5 clay groups, which were compared to 60 reference groups from the surrounding area. Most of the crucible clays came from 2 clay deposits, one of which was located nearby, while the other was situated 50 km away in the Jura region.
The metals casted show a large variety of bronze- and brass-alloys, due to scrap-recycling. Brass making by cementation could be proved in many crucibles.
The crucibles were composed of two layers: a wheel made core of fired ceramic and a lutum layer made of local materials applied to the exterior (and sometimes a thin engobe applied to the interior). In the casting process, the mechanically stabilising and insulating lutum swelled up and vitrified considerably.