From Coin to Medal: A Metallurgical Study of the Brazing Drop on a 19th Century Scudo

Abstract

In the past, it was customary to use out-of-circulation coins as pendants by brazing a peg or ring on the edge of the coin in order to transform it into a devotional or decorative object; this practice was very common for specimens of the Papal States, especially for silver coins. This metallurgical investigation of a 19th century Scudo aimed to relate the internal structure of the coin to the minting technology with a special focus on the brazing drop, in order to provide information on the solidification microstructure arising from a strongly nonequilibrium process such as brazing. The results show that the Ag content in the coin ranges from 92% in the bulk up to 97% on the surface, due to enrichment, while analysis of the brazing revealed that it consists of an Ag-Cu-Zn-Pb alloy, for which the melting temperature has been estimated. Considering the distribution of minor elements, Zn segregates in the secondary (Cu-rich) β-dendrites and inside the whole eutectic structure, while Pb is only present in the Ag-based phases and seems to reduce the solubility of Zn inside the primary (Ag-rich) α-dendrites.