| Abstract: | Examination of a Sican ceremonial tumi, dated to the Middle Sican, c. AD 850–1050, showed that it was made in a silver-copper alloy of approximate composition 93% silver, 6% copper. Many separate pieces are used in the construction, joined together by both mechanical methods and by solder. The principal figure has been made from 18 separate silver sheets, with 169 separate parts identified in the head-dress, totalling 187 design elements. Metallographic examination of a fragment of repoussé decorated sheet from the figure surmounting the tumi surprisingly showed that the silver-copper alloy has a cast morphology; this demonstrates that Sican metalsmiths were pre-casting silver-copper sheet into the dimensions required for making the tumi, rather than carrying out the expected process of making the idol from hammered silver-copper sheet, shaped by extensive cycles of working and annealing, thus contradicting the usual assumptions about the manufacture of sheet-metalwork made in such cases. |
