Dating Archaeological Strata in the Magna Mater Temple Using Solid‐state Voltammetric Analysis of Leaded Bronze Coins

Abstract

The application of solid state electrochemistry techniques for dating archaeological strata using lead‐containing bronze coins is described. The proposed methodology was applied to samples coming from the Roman archaeological site of Magna Mater Temple (Rome, Italy) occurring in different strata dating back between the second half and the end of the 4th century A.D. and the 20th century. The voltammetric signatures of copper and lead corrosion products in contact with aqueous acetate buffer, as well as the catalytic effects produced on the hydrogen evolution reaction, were used for establishing the age of different strata and dating coins belonging to unknown age. Voltammetric data were consistent with a theoretical approximation based on a potential rate law for the corrosion process.

Screening of Iberian Coinage in the 2th‐1th BCE Period Using the Voltammetry of Immobilized Particles

“…This voltammetry is in agreement with previous data of archaeological copper and bronze and leaded bronzes and can be rationalized by considering voltammograms for reference corrosion products and their mixtures. As can be seen in Figure , in which the voltammograms of microparticulate deposits of mixtures of a) cuprite plus tenorite, b) cuprite plus litharge, and c) cuprite plus tenorite plus litharge, are depicted.…”

“…In the first case, in principle equivalent to copper, there would be a primary patina of ‘impermeable’ oxygen‐defective cuprite accompanied by a ‘porous’ secondary patina progressively enriched in tenorite. Accordingly, one can expect an increase of the ratio between the intensities of the signals C 2 and C 1 from deeper to surface layers .…”

“…As described in previous reports , the sampling for VIMP measurements implies the transference of different amounts at the level of few nanograms of materials from the corrosion layers of the coins so that the average composition of the sample depends on the depth reached during the process. The measured currents for the different processes can be taken as proportional to the net amount of the materials responsible of that process.…”

“…Voltammograms were recorded using a CH I660C potentiostat (Cambria Scientific, Llwynhendy, Llanelli UK) and completing the three‐electrode arrangement with a platinum wire auxiliary electrode and an Ag/AgCl (3 M NaCl) reference electrode. For each coin, samples were taken by abrasively pressing onto 1–3 different regions of the coins showing a dark brown uniform hue, as already described .…”

“…In spite of this difficulty, there is the possibility to acquire analytical information of archaeometric interest in series of samples for which it is possible to assume a common or quite similar corrosion history and directing the sampling to regions of the objects presenting homogeneous patination. Under these restricting conditions, previous studies on ten‐cash coins from the last Chinese emperors , and Spanish maravedís minted between 1661 and 1664 , and Roman bronze coins from the Magna Mater temple permitted to establish electrochemical criteria for discriminating between different monetary emissions.…”