The Santi Quattro Coronati by Nanni di Banco: Cleaning of the Gilded Decorations

An optimised laser methodology was devised to clean gilded decorations found on hair and robes of the Santi Quattro Coronati, marble sculptures by Nanni di Banco. The optimisation of laser parameters was achieved through comparative cleaning tests by employing Nd:YAG (1064nm) and Nd:YAP (1340 nm) lasers systems. The different cleaning results were characterised by microscopy, spectral reflectometry, and FT-IR analyses. In particular, high removal control was achieved by short free running (SFR) Nd:YAP and Nd:YAG lasers that allowed gradual cleaning levels. Conversely, a single cleaning level was possible by Q-switching Nd:YAG laser, which also induced an undesired yellowish-orange appearance of the cleaned surface. Following the analysis of these results the whole cleaning treatment of gilded areas was performed using SFR Nd:YAG laser.