Evaluation of the corrosion resistance of bronze patina or/and protective coating on the surface of the archaeological coins.

Archaeological coins are considered essential sources of historical documentation. Over time, they are subjected to corrosion processes that gradually alter their appearance, shape, and composition. This study aims to evaluate the effects of the patina and/or protective coating on the corrosion process. Protection of the original coin surface was crucial following the completion of the cleaning protocol. Various finishes of coin fragments (uncoated, aged, and freshly coated) were investigated to determine their chemical composition, nature of the patina, and corrosion products on their surface using stereo microscopy(SM), X-ray diffraction (XRD), and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDX). The analysis revealed that the coins were composed of a Cu-Sn- and Pb bronze alloy. Furthermore, the efficiency of the patina and/or protective coatings on the coin fragments was evaluated using potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) techniques. The highest protection was achieved for patinated-freshly protective coated fragments, while the most corrosive fragments were those affected by bronze diseases.