INVESTIGATION OF THE STRUCTURE AND PROPERTIES OF THE HISTORICAL TECHNOLOGICAL OBJECTS FROM CAPE ST. ATANAS, BYALA, VARNA REGION

Abstract

Abstract: Archaeological coins constitute a valuable source of information on ancient metallurgical technologies, the microstructure of alloys, and the corrosion processes that have occurred during their prolonged burial in soil. This study presents the results of a microstructural and microchemical investigation of a copper coin of the 40 nummi type issued during the reign of Emperor Justinian I, discovered during archaeological excavations at the Late Antique fortress of Cape St. Athanas, near the town of Byala, Varna Province, Bulgaria. The investigation was carried out using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS). Both the surface layer and the core of the coin were examined to determine their morphological characteristics, microstructure, and local chemical composition. The results indicate that the coin was manufactured from a copper–lead alloy with locally detected arsenic. The surface layer contains copper oxides, lead-rich phases, and corrosion features associated with the diffusion of oxygen and chlorine along grain boundaries. The obtained results demonstrate that the observed microstructural and chemical alterations are related both to the manufacturing technology of the coin and to the long-term corrosion processes that occurred during its burial in a coastal soil environment. The study confirms the applicability of the SEM–EDS technique for assessing the condition, microstructure, and elemental composition of archaeological copper alloys.