Intervention criteria and scientific analysis in conservation of a set of Emiral silver coins from the archaeological site La Ermita del Sacedal, el Rebollar de El Boalo (Madrid)

Abstract

Instrumental analysis techniques are used to identify corrosion products of metal pieces and evaluate their state of conservation: that is, if they are stable or not, and therefore if they are harmful for the future conservation of the piece that we are taking care of. This knowledge, along with other factors that we will describe in our work, allows us to carry out a less interventionist conservation process, close to the principle of minimal intervention. It also moves away from general criteria in cleaning of silver coins, determined in part by Chemical treatments very used in these interventions, which tend to recover the metallic shine hidden under the patinas of the archaeological coins. This is the case at hand: the scientific examination and conservation of a set of silver coins from the Emiral period (9th century) from the archaeological site La Ermita del Sacedal, in El Rebollar de El Boalo (Madrid). The scanning electron microscopy and X-ray energy dispersive analysis confirmed the clay-like deposits adhering to the surface and the composition of the coins and their patina. These analyses revealed a great stability of the patinas, which led us to choose a gentle surface cleaning that would allow a better identification of the inscriptions and the details of the stamp, without altering the patinas of the coins.