Objects from the ancient site of Qalat Rabah (Calatrava la Vieja): a case study on the characterization and conservation of Islamic gilded bronzes from Spain

The recent archaeological excavations at Qalat Rabah (Calatrava la Vieja, Spain) brought to light a number of gilded pieces - harness and personal ornaments - of very high aesthetic and technological quality; these artefacts are being studied from different points of view, as they unquestionably represented the state of the art in the Mediterranean Europe of the Middle Ages. Selected pieces were investigated, mainly by scanning electron microscopy (SEM-EDXA), with regard to the corrosion structures and the gilding technique. The identification of the corrosion products and their distribution provided information for the conservation treatments, whereas the simultaneous presence of gold leaf and mercury lead to hypothesize a hybrid, little documented, gilding technique in which mercury provides the adhesion of the gold leaf to the substrate.