Micro-XRF analysis of silver coins from medieval Poland

•A micro-XRF study of the surface composition of Polish Ag coins was conducted.•The main elements are Ag, Cu and Pb; with Ag concentrations in the 82–98% range.•The results indicate that revaluation probably took place during 995–1031. X-ray fluorescence (XRF) analysis has become a standard method in archaeological science due to its non-invasive and non-destructive nature. This technique has extensively been used for the study of numismatic collections since the data derived from it can be correlated with manufacturing processes, provenance of raw materials, and geographical distribution of ancient mints. A group of 71 silver coins of the first Piasts: Boleslaus the Brave (996–1025) and Mieszko II Lambert (1025–1034) belonging to the collections of the National Museum in Krakow have been characterized using micro-XRF spectrometry. This is the most numerous collection of their coins representing nearly 30% of all known coins from these rulers. The research has focused on evaluating the use of this technique as a screening tool for elemental surface characterization of the alloys. Surveyed coins are mainly constituted by Ag, Cu and Pb along with trace levels of Fe, Ni, Zn, Au, Hg, Bi, and Br. Quantitative analyses have revealed Ag contents in the 81.6–97.5% range for all the evaluated coins. This study had the goal of providing information about the elemental composition of these objects, which will serve to enhance the existing knowledge about geographical and chronological diversification of Polish numismatic collections.