Portuguese silver from the 15th to the 17th century, the 11 dinheiros silver coins

High silver surface contents of high fineness silver coins have been considered in some cases as deriving from very pure silver alloys, being reliable for original bulk composition. Until now, the extent in which surface silver enrichment influences surface analytical results in coins alloys with finenesses greater than the silver content indexed to the maximum value of copper solid solubility in silver (91.2 wt.%) have been disregarded. This investigation, focused on microstructural and compositional characterization of Portuguese 11 dinheiros silver coins, has revealed important surface silver enrichments in high silver fineness coins. In these silver alloys, coin manufacturing process induces a subsurface microstructurally modified layer resulting from intergranular dry and wet corrosion in annealing operations, primarily related to preferential leaching of Cu-rich phase in subsurface depth. This subsurface layer originates a silver overestimation by PIXE and EDXRF analysis, 4 to 7% higher than the bulk of the coins, with unknown elemental compositional gradient and depth that can extend up to to about 70 μm. This study shows, through the combination of different analytical methods, EDXRF, PIXE, SEM-EDS and LA-ICP-MS, that important metallurgical information resulting from the minting process may be missed, when relying only on the judgment of high silver alloys surface analysis. Albeit the existing minor/trace elements compositional gradients between coins surface and bulk, surface contents correlations discriminate distinct silver sources processed during the 15th to 17th centuries in Portugal, from different historical periods and mints, Lisbon and Porto. Gold/bismuth ratios related to the processed silver initial composition and lead/bismuth ratios related to the silver metallurgical processes, are important discriminators of these high silver alloys. Mercury appears also to be an important element for the discrimination of silver alloys sources. Portuguese minting depended and relied on different silver sources during the 15th to 17th centuries. European silver with high Au and Hg, and low Pb and Bi contents, supplied the oldest chronologies of Dom Afonso V and Dom João II in the 15th century, being replaced at the dawn of the 16th century by a new precious metal entering the Portuguese capital, with low Au and high Bi contents, probably derived from argentiferous copper ore sources processing. In the 2nd and 3rd quarters of the 16th century, minor/trace elements contents of Lisbon and Porto mints evolve towards the compositional homogenization observed in Dom Sebastião I period, probably due to major recycling operations of the earlier currency realized in each kingdom. Philippine chronologies reveal the presence of the new discovered Potosí American silver, introduced in Portugal by Dom Filipe I (Felipe II of Spain), distinguishable from the European silver in use until 1578 in the Portuguese territory, by Au contents < 100 ppm and very low Bi contents. Potosí silver is identified for the first time through a superficial analytical method, such as PIXE, rather than by NAA multielement global analysis