Roman and Medieval Litharge Cakes : A Scientific Examination
Author(s): Brice Girbal
The refining of silver alloys to obtain the silver they contain (cupellation) has been undertaken for thousands of years. The primary material evidence for this process comprises a lead-rich waste known as litharge cakes. Studies conducted by Bayley and Eckstein (2006) and Bayley (2009) suggested that cupellation in the medieval period was more successful/advanced than in Roman times based on the higher PbO/Cu2O ratio in the medieval litharge cakes. The analyses of a further forty five litharge fragments from twelve archaeological sites has found no correlation between the PbO/Cu2O ratio and time period. The microstructural and chemical analyses showed that there were two major compositions; a clay/vegetable ash mixture and bone ash. No correlation was identified between hearth lining composition and the PbO/Cu2O ratio. However, it is argued that the clay/vegetable ash was more absorbent than the bone ash litharge cakes. It was also noticed that 90% of the medieval litharge was clay/vegetable ash while they accounted for only 50% of the Roman litharge. This may be indicative of a compositional preference in certain time periods. Unfortunately the dating is poor in most cases limiting more comprehensive interpretations. Nevertheless there is no evidence to suggest a more effective practice at either period.
- Report Number:
- 51/2011
- Series:
- Research Department Reports
- Pages:
- 80
