Photo: the north transept of the Papal Basilica of Saint Peter in the Vatican, pilot site for the restoration of the stuccoes © Fabbrica di San Pietro

The gilded stucco decoration of the vault of the Papal Basilica of Saint Peter in the Vatican is the result of a complex historical stratification that began in the second half of the sixteenth century and continued, through rebuilding and maintenance campaigns, into the twentieth century. The extent of the surfaces and the variety of execution techniques make this decorative ensemble one of the most complex in the entire building. The pilot site carried out in 2024 in the north transept made it possible to define an intervention methodology based on the integration of historical analysis, direct observation, and scientific investigation. The observations and analyses revealed the presence of metal armatures composed of large-headed nails and brick fragments fastened with copper wire, the use of traditional lime-based mortars with local pozzolans for the core layer, finished with marmorino and followed by the application of mordant gilding. The deterioration phenomena vary according to the construction phases, with predominantly structural problems in the metal armatures of the older stuccoes and greater surface and gilding deterioration in the eighteenth-century ones.

On the basis of the data collected, the project was developed according to the principles of minimal intervention and reversibility, providing for operations of stabilization, selective cleaning, consolidation, re-adhesion of layers, and formal integration of losses.

All phases of research and restoration will make use of digital technologies (H-BIM) capable of integrating, within a single virtual environment, metric data, images, work and laboratory reports, monitoring outputs, and archival historical documentation.

Although no evident structural failures are currently visible, a proposal has been developed for the adoption of an optoelectronic structural monitoring system with FBG (Fiber Bragg Grating) fiber-optic sensors for the stuccoes of the north and south transepts, in order to detect early warning signs of possible detachments. The system is particularly well suited to monitoring the deformation of wrought-iron nails caused by oxidation phenomena, allowing continuous data acquisition, the activation of alarm thresholds, and support for predictive maintenance strategies.

The conference in Italian Gli stucchi dorati della volta della Basilica Papale di San Pietro. Studi preliminari per la progettazione degli interventi conservativi (The gilded stuccoes of the vault of the Papal Basilica of Saint Peter: preliminary studies for the planning of conservation interventions) will bring together four speakers: Giovanni Nicoli, Giovanni Cavallo, Alberto Capitanucci, and Valerio Vezzari. It will take place on Monday, March 16, 2026, at 16:00 in room A2.14, on the second floor of the SUPSI Campus of the Department of Environment Constructions and Design (via Flora Ruchat-Roncati 15, Mendrisio). Admission is free.

The event is part of the series of public cultural lectures promoted by the Conservation and Restoration area of SUPSI within the Department of Environment Constructions and Design – an area represented by the Bachelor of Arts in Conservation, the Master of Arts in Conservation-Restoration, and the Institute of materials and constructions, with its research field dedicated to conservation and restoration. These conferences, addressed to students as well as to all interested members of the public, are intended as an opportunity to reflect on our heritage, art, and culture.