Multi-technique approach to evaluate the effect and durability of biocides treatments on Peperino stone in the “Basilica San Francesco alla Rocca” (Viterbo, Italy)

Consolidation and biopatinas control represent two main concerns in outdoor stone cultural heritage conservation. The work was developed in the framework of the COLLINE project (https://www.enea.it/it/fusione-e-sicurezza-nucleare/progetto-colline) whose aim is to develop, test and evaluate in real conditions and on the monuments being restored, a recovery protocol for degraded stone surfaces thanks to the synergistic use of innovative materials for conservative restoration, modern and innovative diagnostics and techniques and sensors and computerization of data,, updated in real time, for remote monitoring and management. Three low-impact products for biopatinas removal have been applied on Peperino stone, an Italian volcanic tuff, used for the construction of several architectural and sculpture elements in Viterbo and Central Italy. The hexagonal pulpit of the “Basilica San Francesco alla Rocca” was selected to perform the investigations. This study aimed to investigate and test the efficiency and stability of the treatment with DMSO-based gel, essential oils (BioTersus) and enzymes (Nasier) in removing the biological patinas. Color measurements, VIS-NIR-SWIR reflectance spectra (400-2500 nm) and hypercolorimetric multispectral imaging data were acquired before and after the cleaning process to characterize the distribution and concentration of the biological patina on the designed areas and to develop a monitoring model that simultaneously detects the biological activity and the efficiency of the considered low-impact products. In this study, the results show that combining different analytical approaches with chemometric modelling can lead to develop a fast, reliable and robust quality control approach that can be used to characterize and monitor in situ coating products in a non-destructive method.