The Bizantine door in the basilica of St. Paul Out of the Walls in Rome: compositional study of the alloys and interpretation of the results in view of its restoration

This work concerns the bizantine door in the Basilica of St. Paul out of the Walls, in Rome. Made in Constantinople in 1070, it was given to the Basilica by Pantaleo de Maurone Comite. The door was seriously damaged in 1823 by the fire, which reduced it in pieces and caused irreversible changes in both the structure and the aspect of metals; in 1965 it was reassembled and the missing parts were reconstructed. The door is made of copper alloys containing zinc and is decorated by silver agemina. In the context of scientific investigations planned for the restoration of this important monument, a compositional study on both the original and the added parts was carried out. A portable XRF (X-Ray Fluorescence) spectrometer was used for an in situ non-destructive campaign. Three main groups of alloys were identified: the original parts, the added parts and the parts reconstructed in 1965; differences were also found between the original and non-original ageminae. The main outcome of this investigation was the choice of a cleaning procedure that gave a homogeneous aspect to different parts of the door. Following this preliminary work, 34 samples were analyzed by ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy), in order to measure the concentration of major, minor and trace elements. Among other significant results, it was observed that the compositional pattern, characterised by arsenic, nichel and antimony, is typical of polimetallic minerals common in Anatolia.