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

Abstract

A collection of ancient Roman orichalcum coins, i . e ., a copper-zinc alloy, minted under the reigns from Caesar to Domitianus, have been characterised using scanning electron microscopy (SEM-EDS) and electron microprobe analysis (EMPA). We studied, for the first time, coins emitted by Romans after the reforms of Augustus (23 B.C.) and Nero (63–64 A.D). These coins, consisting of asses , sestertii , dupondii and semisses , were analysed using non- and invasive analyses, aiming to explore microstructure, corrosive process and to acquire quantitative chemical analysis. The results revealed that the coins are characterized by porous external layers, which are affected by dezincification and decuprification processes. As pictured by the X-ray maps, the elemental distribution of Cu and Zn shows patterns of depletion that in some cases penetrate in deep up to 1 mm. The composition of the un-corroded nucleus is a Cu-Zn alloy containing up to 30% of Zn, typical of coins produced via cementation process.

Solid-state electrochemical characterization of emissions and authorities producing Roman brass coins

“…Moreover, all the samples present small pores and cracks lines, due both to mechanical stress and corrosion process. The patterns are comparable to the one previously described [44], especially for the samples 2, 236, B15 and E5 that cannot be analysed using destructive techniques, e.g. EMP analysis on cross sections.…”

“…EMP analysis on cross sections. EMP analysis (Table 2) were acquired in the un-corroded metallic nucleus of a sub-set of 11 sacrificed coins, i,e., sectioned as already reported [44]. The content of Zn ranges between 15% and 30% with the concomitant variation in the percentage of Cu, as can be seen in Figure 4.…”

“…Studies on metal coins are focused on the determination of the composition and microstructure of the base alloy and the identification of the corrosion products using multi-technique approaches some of which require some destructive sampling [43][44][45]. In this context, we applied the VIMP methodology in order to acquire archaeometric information based on a minimally invasive (at the nanogram level) sampling on the metal patina.…”

Recent Advances in Protective Coatings for Cultural Heritage–An Overview

“…Brass, or orichalcum in ancient times, is a Cu-Zn alloy. Romans produced brass coins improving the cementation process-the zinc vapours spread into the copper melt, obtaining an alloy with approximately 30% zinc and 70% copper [12]. The most important problem regarding the corrosion of brass alloys is the dezincification phenomenon, which is still being investigated.…”

Shining Like Gold and New: The Emergence of Brass North of the Alps Around the Turn of the Era.

“…The original brass produced by Roman workshops in the rst half of the 1 st century BC with very distinctive composition and material properties has been referred to as the aurichalcum [1,4,7]. Thanks to modern analytical tools, there has been some progress in identifying brass manufacture (possibly from the Roman imports) in the broader area of Europe among the objects dated already to the early 60s BC; however, their geological provenance remained mostly undetected [16,17,2,18,9]. More recently, studies systematically dealing with the Pb isotope compositions of selected materials, such as copper [19,20,21,22], lead [24,25], and brass [2], have become available.…”