Microstructural Investigations Support the Revised Minting Chronology of Saracen Head Denarii Issued by Louis I of Hungary

At the beginning of the reign of Louis I of Anjou, King of Hungary (1342–1382), various types of currency were introduced, undergoing repeated devaluations until 1360. According to Lajos Huszár, denarii of the Saint Ladislas type were issued in 1358–1371, with a fineness of approximately 0.93, whereas Saracen Head denarii were assigned to 1373–1382 and described as being of lower fineness. Recently, Csaba Tóth claimed that the Saracen’s Head Denarii were issued in the middle of the reign of Louis I, and the last types of denarii were those with the representation of Saint Ladislas. A recent archeological find from Transylvania (Romania) contains 3 intact Saracen Head denarii and 12 fragments and only 3 fragments of Saint Ladislas denarii. The significant number of fragments facilitates advanced microstructural investigations of the bulk alloy, including XRD correlated with SEM microscopy and EDS elemental spectroscopy. It results in a silver content of about 89.15 ± 0.93 wt.% for Saracen Head denarii, while Saint Ladislas ones have a significantly decreased fineness of 81.75 ± 2.54 wt.%. These values support the newest chronology discussed in the literature, placing the Saracen Head denarii in the middle of Louis I of Anjou reign, while the Saint Ladislas type belongs to the latest part of the reign. Patina layers were investigated regarding the resting ground, which contains quartz, clays (kaolinite and muscovite mixture), and calcite. Thus, the oxidized layer formed directly on the metallic surface is dominated by copper oxides, which further interact with the calcium carbonate from the soil generating a green layer of malachite. This layered corrosion extracts copper from the outermost layers, causing significant silver enrichment of the coin’s surface of about 97 wt.%, which affect nondestructive investigations. The slight micro-incision of the fragment’s sides enabled accurate measurement of the silver fineness despite the presence of corrosion features. Such an approach could be applied for evaluation of other coins’ fineness performing the micro-abrasion on their edges, allowing for SEM-EDS measurements while preserving the visual integrity of coins.