Construction technology and raw materials for the restoration of Gian Lorenzo Bernini's Cornaro Chapel Vault, Rome (Italy)

The scientific and multidisciplinary approach to the restoration of Bernini's Cornaro Chapel, at Santa Maria della Vittoria church in Rome, is reported as a fruitful example of the synergic cooperation between scientists and restorers for the planning and implementation of suitable conservative interventions. This study reports the cycle of scientific and diagnostic investigations carried out on the great Baroque masterpiece before the restoration started in 2020. Before the restoration, the technique of execution, the raw materials, and the state of preservation of Bernini's extraordinary sculptural cycle were scrupulously investigated with different and complementary analytical techniques on suitably selected micro-samples. Specifically, the original constituent materials were characterized, sometimes together with those resulting from decay processes or previous restoration interventions, through different techniques such as polarizing optical (OM) and fluorescence microscopy (FM), Electron Probe Microanalyses (EPMA) coupled with Energy Dispersive Spectrometry (EDX) and Fourier Transform Infrared Spectroscopy (FT-IR). Particular attention was paid to the frescoed vaulted ceiling of the chapel, enriched by scenes modeled in white stucco and gilding, to better understand the manufacturing as well as the accuracy adopted by Bernini in layering, investigating from the most superficial to the innermost layers. Scientific and diagnostic analyses were successfully performed to design the most convenient restoration intervention, to verify its correctness and ensure the use of non-invasive cleaning and conservative procedures. The results obtained from nine micro-samples, mainly composed of stucco and fragments of frescoes, contributed to dispelling the doubts raised by restorers, especially regarding the use of specific raw materials (notably the gilding, type of binder and aggregates, superficial patinas, etc.) and the presence of retouches in certain areas of the masterpiece, deriving from previous conservation interventions. The identification of these raw materials and the layering of the samples supported cleaning and restoration interventions through the use of suitable materials compatible with the originals.