We investigated the characteristics of a group of 13 Middle Iron Age egg-shaped crucibles and crucible fragments from Tilburg (The Netherlands). We used a combination of optical and chemical analyses, including hand-held XRF, microCT scanning and 3-D printing polarizing light microscopy and SEM-EDX. The chemical analyses confirmed that the crucibles were used for copper alloy metallurgy. Impressions in the lids of the crucibles turned out to be imprints of copper alloy scrap, including fragments of twisted wire and fibulae. Most remarkable, however, is the large proportion of sheet metal among the scrap.

In order to make crucibles from the local, non-refractory clays, a hitherto unknown ceramic-faience hybrid was used: A combination of clay and halophytic plant ash was mixed with silt into a paste, and this was used to construct the crucible. During firing, the flux would promote melting of the clays and probably prevent catastrophic failure of the crucibles. The resulting glassy groundmass – in which silt grains are embedded and partially dissolved – is rich in Al2O3 as well as in Na2O, K2O, CaO, MgO and Fe2O3.

It is likely that this technique of crucible manufacture was widespread in Late Prehistory in areas where no refractory clays were available. ... Read more

Desktop micro-CT scanner has become a standard piece of equipment for many materials science laboratories and is increasingly popular in the field of archaeology for the study of archaeological soils and small archaeological artefacts. The technique does have limitations which are reviewed. Then, the usefulness of desktop Micro-CT scanners for the study of archaeological artefacts is demonstrated in a non-destructive study of manufacturing methods of Roman and Early Medieval monochrome and polychrome glass beads. Differences in glass colours show up in these scans as differences in attenuation. The presence and distribution of bubbles and various inclusions (metal, opacifier) are also well visible. Shaft shapes and patterns of bubbles inside the glass make it possible in most cases to distinguish between drawn, wound and constructed (millefiori) beads and to study shaping methods. Shafts shapes also reveal shapes and dimensions of the mandrels used in bad manufacture. Decoration and construction methods are be visualized and studied in virtual cross-sections and semi-3D rendered images of selected glass colours. Visible degradation processes - including fissuring, leaching (especially of opaque yellow glasses) and dissolution processes - are highlighted. The micro-CT scans demonstrate how quality of raw glass, base design and workmanship ion bead manufacture have improved with time. Moreover, it shows how these scans may serve as basis to discuss the organization of workshops where simple or more complex objects were made from non-metallic raw materials, and the availability and distribution of different qualities of raw materials for these workshops. ... Read more