X-ray line ratios and double-ratios to non-destructively probe surface gold enrichment in gold alloys.

The presence of surface layers with altered chemical composition in gold alloys is investigated exploiting X-ray line ratios populated in energy-dispersive X-ray fluorescence investigations. We show that the use of the Ag (L α /K α) X-ray ratio and the Ag (L α /K α)/Au (M α /L α) double-ratio allows to ascertain surface gold enrichment that can be attributed to a depletion of silver concentration in a thin (< 1 μ m) surface layer of the material. The formalism developed in this paper is exploited to probe the chemical composition of precious protohistoric gold findings belonging to the largest complex of Bronze Age gold ornaments ever found in Italy. The results support the findings of complementary micrography investigations, performed on the same collection, and are relevant to contribute to understanding techniques used in ancient metallurgy. • X-ray line ratios and double-ratios can be effectively used to non-destructively probe material surface layers. • The proposed framework can be exploited to analyze materials with even particularly thin surface alteration. • We analyze precious gold findings dated to the Final Italian Bronze Age. • Artifacts with a thin (< 1 μ m) gilding, due to depletion of the silver concentration, are identified. • The findings are relevant to archaeometallurgical studies. [ABSTRACT FROM AUTHOR]