Archaeology of Lisbon Old City: ceramic crucibles from pre-XVIIIth century metallurgical foundries

During an emergency archaeological intervention conducted in downtown Lisbon (the Old City), ceramic foundry crucibles were collected in a layer of embankment debris used after the earthquake that destroyed the city in 1755. A chemical and phase-constitution study was undertaken to complement the dating and to ascertain the kind of foundries (metallurgical or glass-working) concerning two intact cup-shaped crucibles and a fragment displaying glassy outflows. Non-destructive methodologies were used – namely, laboratory techniques (X-ray fluorescence spectrometry and X-ray diffraction) combined with synchrotron-radiation-induced micro-fluorescence (SRXRF). Analytical results are presented and discussed. SRXRF analysis of the glassy outflow on the larger crucible revealed the presence of mercury and traces of gold, along with copper, suggesting that it might have been used to manipulate gold amalgams. A possible Islamic origin was disclosed for the smaller crucible as only tin was detected in the external outflow and further confirmed by minute cassiterite (SnO2) grains.