FIB-FESEM and EMPA results on Antoninianus silver coins for manufacturing and corrosion processes

Abstract

A set of ancient Antoninianus silver coins, dating back between 249 and 274 A.D. and minted in Rome, Galliae, Orient and Ticinum, have been characterized. We use, for the first time, a combination of nano-invasive (focused ion beam-field emission scanning electron microscopy-X-ray microanalysis (FIB-FESEM-EDX), voltammetry of microparticles (VIMP)) and destructive techniques (scanning electron microscopy (SEM-EDX) and electron microprobe analysis (EMPA)) along with non-invasive, i.e., micro-Raman spectroscopy. The results revealed that, contrary to the extended belief, a complex Ag-Cu-Pb-Sn alloy was used. The use of alloys was common in the flourishing years of the Roman Empire. In the prosperous periods, Romans produced Ag-Cu alloys with relatively high silver content for the manufacture of both the external layers and inner nucleus of coins. This study also revealed that, although surface silvering processes were applied in different periods of crisis under the reign of Antoninii, even during crisis, Romans produced Antoninianus of high quality. Moreover, a first attempt to improve the silvering procedure using Hg-Ag amalgam has been identified.

Microstructure and chemical composition of Roman orichalcum coins emitted after the monetary reform of Augustus (23 B.C.)

“…The corrosion of orichalcum is associated with dezincification and decuprification processes 21–23 , which can occur for several microns in depth; therefore, to evaluate the degree of corrosion it is necessary to analyse cross section of samples “from rim-core-to-rim” 24,25 .…”

“…Recently, EMPA technique was used obtaining quantitative chemical analysis of Roman alloys used for coinage 25 .…”

Microchemical surface analysis of historic copper-based coins by the combined use of FIB-FESEM-EDX, OM, FTIR spectroscopy and solid-state electrochemical techniques

“…Archaeometrical studies can also probe the application of specific minting techniques, such as plating [3], to produce forgeries [4], and to also reduce costs while producing official money during periods of crisis. Examples of this last practice can be found in the Roman Republic in the production of nummi (308-311 A.D.) at Carthago [5] during the Roman Imperial period in the production of Antoninians introduced by Caracalla (Marcus Aurelius Antoninus Pius) in 215 A.D [6], or in Renaissance coins minted in Gubbio (Italy) [7].…”

“…FTIR identifies organic compounds. In particular, FESEM-EDX provides morphological data, elemental compositions and deep profiles on trenches performed with FIB [6]. The combination of both techniques enables a nanoinvasive method as the loss of matter in trenches is of only a few ng.…”

Chemical composition of small fragments of metals from Castillo de Huarmey (Peru): Chemical analysis in the micro‐area using FE‐SEM‐EDS, FE‐EMPA and XRD

“…2007) and an electron microprobe analyser with field emission (FE‐EMPA) (Frame 2010; Orfanou and Rehren 2015; Doménech‐Carbó et al . 2018; Bugaj et al . 2019) are applied.…”