Investigation of surface silver enrichment in ancient high silver alloys by PIXE, EDXRF, LA-ICP-MS and SEM-EDS

A Multi-Analytical Approach on Silver-Copper Coins of the Roman Empire to Elucidate the Economy of the 3rd Century A.D

In this study, 160 silver-copper alloy denarii and antoniniani from the 3rd century A.D. were studied to obtain their overall chemical composition. The approach used for their characterisation is based on a combination of physical, chemical, and chemometric techniques. The aim is to identify and quantify major and trace elements in Roman silver-copper coins in order to assess changes in composition and to confirm the devaluation of the currency. After a first cataloguing step, μ-EDXRF and SEM-EDX techniques were performed to identify the elements on the coins’ surface. A micro-destructive sampling method was employed on a representative sample of the coins to quantify the elements present in the bulk. The powder obtained from drilling 12 coins (keeping the two categories of coins separate) was dissolved in an acidic medium; heated and sonicated to facilitate dissolution; and then analysed by ICP-AES and ICP-MS. The two currencies had different average alloy percentages; in particular, the % difference of Ag was about 8%. The other elements were found in concentrations <1 wt%. Of these, the element highest in concentration were Pb and Sn, which is in agreement with the literature. The multivariate analysis performed on the data acquired revealed two groups of coins, corresponding to the two currencies.

Influence of sample surface topography on laser ablation process

In this work we discuss how sample surface topography can significantly influence the laser ablation (LA) process and, in turn, the analytical response of the LA Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) method. Six different surface topographies were prepared on a certified aluminium alloy sample BAM 311 and SRM NIST 610 to investigate the phenomenon. All the samples were repetitively measured by LA-ICP-MS using a spot by spot analysis. The effect of laser fluence in the range of 1-13 J/cm² was studied. For majority of measured isotopes, the ICP-MS signal was amplified with roughening of the sample surface. A stronger effect was observed on the Al alloy sample, where the more than sixty-time enhancement was achieved in comparison to the polished surface of the sample. Since the effect of surface topography is different for each analyte, it can be stated that surface properties affect not only the ICP-MS response, but also elemental fractionation in LA. The presented results show that different surface topographies may lead to misleading data interpretation because even when applying ablation preshots, the signal of individual elements changes. The utmost care must be taken when preparing the surface for single shot analysis or chemical mapping. On the other hand, by roughening the sample surface, it is possible to significantly increase the sensitivity of the method for individual analytes and supress a matrix effect.

European Silver Sources from the 15th to the 17th Century: The Influx of “New World” Silver in Portuguese Currency

The circulation trading routes and the characterization of the silver metal used in the European continent in the 15–17th centuries are historical issues that are still open. This study aimed to bring an insight into the silver processed within a chronological framework in the Portuguese territory, relating the analytical data with the known historical information. This investigation developed on 230 high silver coins from two important Portuguese coin collections was based mainly on surface particle-induced X-ray emission (PIXE) analysis, complemented with a few energy-dispersive X-ray fluorescence (EDXRF) analyses. The silver processed in different timelines was discriminated based on the variation of the impurity contents, namely Au and Bi. European silver with high Au and Hg and low Pb and Bi contents supplied the 15th century chronologies, being replaced at the dawn of the 16th century by a new metal entering the Portuguese capital. This new metal, with low Au and high Bi contents, was probably derived from European argentiferous copper ores. By the end of the 1500s, the Philippine chronologies reveal the newly discovered Potosí silver, identified for the first time based on PIXE minor and trace element surface contents, distinguishable from the European silver in use until 1578 in the Portuguese territory, by Au contents <100 ppm and very low Bi contents.

Comparison of PIXE and XRF in the analysis of silver denarii of the early Piast

The collection of denarii from the time of development of a Polish medieval state was studied using the proton induced X-ray emission spectroscopy. The major elements detected for these denarii are Ag and Cu, while minor elements such as Pb, Fe, Au, Bi, and Zn may also be present. The aim of the study was to cross-compare the results with a previous micro-X-ray fluorescence data and to perform a better quantification of the denarii elemental composition, especially for trace elements, providing suggestions of the origin of alloy compounds.