An estimate of the minting method of three silver coins of the 3rd century B.C. through their microstructural study

The microstructure of three silver coins of the 3rd century B.C. from the Illyrian King Monounios and the ancient Greek cities of Dyrrachion and Corcyra, belonging to the Kreshpan hoard, was determined with X-ray diffraction and transmission electron microscopy in order to investigate their minting method. It is deduced that the coins are characterized by a large number of structural defects, mainly dislocations, twins and microtwins, which in some cases were bent. These crystal defects are common in each of the coins examined. This information allowed the formulation of a possible minting method. Since twins in FCC metals are formed with thermal treatment, and mechanical twinning is rather improbable, it seems that the coins were initially hot-worked. Bent twins indicate that working continued during cooling. Especially for the Corcyra coin it was deduced that it was treated at higher temperature or its cooling rate was lower.