CORROSIVE EFFECT OF ROLLING FAULTS INDUCED BY MICROSTRUCTURAL SEGREGATIONS IN A SILVER COIN ISSUED BY GABRIEL BETHLEN IN 1626

Abstract

Gabriel Bethlen’s monetary reform in 1625 supposed to replace bad coins with good-quality silver issues. Some of these coins exhibit small, parallel surface lines caused by rolling faults in silver plates. This study investigates a 1626 silver groat minted at Baia-Mare, displaying prominent scratches extending from obverse to reverse. XRD and metallographic analyses reveal copper grain’s oxidation to Cu₂O, localized compositional inhomogeneities, and lamination-induced micro-cracks resulting from silver-copper segregation. The coin’s high relief is worn due to the circulation while the lower areas preserve the initial state. Metallographic observation reveal that the lower relief contain silver (83.7 wt.% α phase and eutectic) while the worn areas contains debased silver (65.5 wt.% eutectic and β grains) generating large copper micro – segregations, confirmed by SEM – EDX. These structural defects facilitated corrosion across the rolling direction, becoming more visible after coin cleaning. Such micro faults would have been undetectable after coin issue. The findings indicate that such pseudo-scratches represent not mechanical damage or intentional markings, but metallurgical anomalies associated with subtle debasement practices. This may suggest a controlled attempt to conceal minor reductions in silver fineness during Bethlen’s monetary reform, intended to stabilize coin production while preserving the coin’s visual and fiduciary integrity.