From Calves' Sculls to finished Bone-Ash Cupels and testing of Precious Meetals. An Investigation of the cupellation in the Mint in the Archbishop's Palace, Trondheim, in medieval times

Abstract

The paper discusses three topics: (1) the production process of bone-ash cupels from bones in calves’ sculls to finished cupels, (2) cupellation of a silver and a gold alloy with known compositions in replica cupels and (3) how lead oxide is distributed in the cupel after cupellation. Following the precept of Ercker in his treatise published in 1574, the authors’ production of cupels is described in detail, from boiling the calves’ heads to the finished cupels, each with a fine-grained surface layer. The microstructure of bone-ash particles and the flow of molten lead oxide into the cupel in a replica cupel and a cupel found during the archaeological excavations in the Archbishop’s Palace, Trondheim, in 1991–1995 are compared. The experience gained from making cupels and later use of the cupels for cupellation led the authors to the conclusion that the cupels found during the archaeological excavations on the premises of the 16th century Mint in the Archbishop’s Palace were probably produced locally at the Mint. By using his own cupels, the contemporary moneyer might have measured the fineness of precious metals with an acceptable degree of precision.