Metallographic investigations of a Roman fibula from Carnuntum, Austria

Abstract

In the 1950 s a Roman fibula head was found in Carnuntum and presently examined by metallography. 3D digital microscopy (3D-DM) was used to show the ornaments on the surface. Due to the complexity of the fibula head, a micro-computed tomography (CT) was carried out. The CT scan already showed that the fibula head consisted of at least four individual pieces. Subsequently the fibula part was cold embedded under vacuum and then prepared for further metallographic investigations. Light optical microscope (LOM) and scanning electron microscope (SEM) with energy-dispersive X-ray analysis (EDS) were used. The investigations showed that not less than four different copper alloys were used for the fibula head. The bronze alloys are very different, which suggests the use of various starting materials including recycled copper alloys. The microstructure of the bronzes is uniform and—depending on their compositions—contains precipitates like Pb and the intermetallic phase Cu<inf>41</inf>Sn<inf>11</inf>. The corrosion layers exhibit a pronounced Sn enrichment and contain most likely malachite as well as locally both cuprite and azurite. On some surfaces, textile fibers were embedded in the corrosion layer, which indicate that a textile fiber was in contact with the fibula during corrosion.