Alchemy in Mannheim? – Mineralogical and chemical analysis of 17th-18th century technical ceramics and lead glazed earthenware.

This presentation focuses on technical ceramics from various early Modern dumping contexts ranging from a well to latrine and surface fills within in the former city walls of Mannheim.

Additionally domestic glazed earthenware from a latrine fill were analysed that exhibited alterations to surface texture and colour or were covered with residues which were hypothesised to be affiliated to chymistry practices during this period.

The analytics were performed using a combination of chemical analysis via micro-X-Ray Fluorescence (µXRF) and/or Scanning Electron Microscope with Energy Dispersive Spectroscopy (SEM-EDS) as well as mineralogical analysis via micro-X-Ray diffraction (µ-XRD2), to determine the nature of pyrotechnological processes as well as the source of alterations and residues. Technical ceramics were further analysed via ceramic petrography to define their technological characteristics, including refractoriness and the pyrotechnological processes in which they were used.

Preliminary results suggest that while most of the glaze alterations seem to be caused by weathering processes during burial, some may be related to misfiring or refiring processes. Jarosite was identified at the surface of some domestic ceramic fragments and might be connected to separation processes in precious metal working but could be formed by weathering as well. However, iron and alkaline rich slags with specks of precious metal alloys further strengthen this interpretation. Other crucibles contained slags indicating pale ore assaying.