ABSTRACT
This paper refers to the conservation work in progress in Florence, at the Opificio delle Pietre Dure, on the bronze elements from the Baptismal Font of Siena (1417-1430). In the bronze conservation community, it is well known that the laser cleaning of gilded bronzes was developed during the restoration of the Gates of Paradise by Lorenzo Ghiberti and it was subsequently adopted for the restoration of the other doors of the Florentine Baptistery. Since then, laser ablation has been used for various cases and materials, whether involving or not surface gilding. In this new case study, the focus of the cleaning of large amalgam gilded surfaces was on indoor stored artworks that underwent various maintenance procedures with different materials. The consequent conservation issue concerns the interaction of metal substrates with altered organic coatings (such as waxes, oils and varnishes) and the effects of some drastic cleaning methods operated in the past. The method selected by the conservation team was based on a combined approach to remove altered materials from the surface. Particularly effective was a preliminary step based on the treatment with steam and the use of “oil in water” emulsions, which allowed to partially remove the organic layers and to proceed with lower fluence laser cleaning. The selection of the laser type and the optimization of the operating parameters, along with scientific investigations aimed at the characterization of surface materials and monitoring of ablation, have led to a deeper awareness of some operating solutions.
