Electrochemical Characterization of Coinage Techniques the 17^th Century: The maravedís Case

Abstract

The voltammetry of immobilized particles (VIMP) methodology was applied to the discrimination of Spanish maravedis produced in 10 different mints between 1661 and 1664 using characteristic signatures for the reduction of cuprite and tenorite in the patina of the coins and catalytic effects on the hydrogen evolution reaction (HER). The variation of the apparent tenorite/cuprite ratio with depth was fitted to potential laws differing from one mint to another for A Coruña, Burgos, Córdoba, Cuenca, Granada, Madrid, Trujillo, Segovia, Sevilla and Valladolid coins. Electrochemical data permitted to detect the changes in the composition (with lowering of the silver content) and manufacturing technique (from hammer to mill) occurring in this historical period.

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 .…”

“…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.…”

Estudio arqueométrico de maravedís de Felipe IV (1660-1664)

“…Cada elemento metá-lico de la muestra presenta una respuesta voltamperomé-trica característica que permite su identificación cualitativamente pero no su proporción. Este método analítico ha sido aplicado previamente a otras colecciones numismáticas y ha sido utilizado para determinar procedencias de materias primas, caracterizar técnicas de fabricación y discriminar entre diferentes series de monedas y/o cecas como se ha descrito en trabajos recientes (Doménech Carbó 2014;Doménech-Carbó et al 2017b;Di Turo et al 2017), incluyendo unos primeros resultados sobre maravedís (Doménech-Carbó et al 2017c).…”