Near-surface Enrichments on Roman Imperial Silver Coins by X-ray Spectral Analysis and Auger Depth Profiling

摘要

The contents of silver and copper in near-surface layers of six Roman silver coins covering the Imperial era were determined by two different methods of X-ray spectral analysis, and depth profiles were recorded for silver and copper by Auger electron spectrometry with ion sputtering. Coins of Vespasianus and Marcus Aurelius have a high silver content of ca. 94 wt percent being constant in depth down to 10 mu m. In contrast, coins of Hadrianus and Septimius Severus show silver contents going down from 93 percent at the surface to values of 86 and 70 percent, which are reached in a depth of 7 and 12 mu m, respectively. The surface-enrichment of silver is surprising for the Hadrianus coin (ca. 136 A.D.), because it belongs to the early Imperial era. Coins of Gordianus (ca. 242 A.D.) and Gallienus (ca. 264 A.D.) are covered by layers highly Ag-enriched but only 1 to 2 mu m thick, and have a Cu-based core with silver contents of only 20 and 10 percent, respectively.