Analysis of counterfeit and regal copper coins from the sloop-of-war HMS Swift (1770), by means of SEM, EDXRS and WDXRF

VÁZQUEZ, CRISTINA; CIARLO, NICOLÁS C.; CUSTO, GRACIELA; ORTIZ, MARTA; DE ROSA, HORACIO; ELKIN, DOLORES

Lisboa

Workshop; 2nd International Workshop Physical and Chemical Analytical Techniques in Cultural Heritage; 2012

Centro de Física Atómica da Universidade de Lisboa

Coins counterfeiting, particularly the forgery of regal coins, achieved remarkable expansion in Britain and its overseas territories during the eighteenth century. Despite of the regulations established for the issue, and the penalties implemented, the use of this type of exchange went on to become an everyday activity. This paper presents the physico-chemical characterization results of four supposed copper coins recovered from the sloop-of-war HMS Swift (1770), sunk in Puerto Deseado (Santa Cruz province, Argentina) [1]. The optical stereomicroscopy observations allowed to identify the three largest coins as halfpennies of George Rex. Based on some characteristics of the effigy and the exergue numbers, one of them was assigned to the period of George Rex II (1727-1760), probably 1753 [2]. On the basis of its dimensions, the smallest piece was classified as a farthing. Scanning electron microscopy (SEM), energy and wavelength dispersive X-ray spectroscopy (EDXRS and WDXRS), non-destructively performed, allowed to determine several diagnostic features. The three halfpennies present a dendritic microstructure ―as a product of solidification due to a process of alloy melting and casting in a mold―, and a chemical composition corresponding to copper alloys with tin, zinc, iron and lead added in different quantities. The farthing, instead, was made of pure copper, and probably coined. Besides, the three halfpennies ―unlike the farthing―, do not fulfill the regal standards of that time (i.e. coined in pure copper, using a disc ―blank― obtained from a rolled plate). It can be concluded that the halfpennies are forgeries, all of them probably made in the early years of George Rex III reign (1760-1820).