Hi-tech restoration by two-steps biocleaning process of Triumph of Death fresco at the Camposanto Monumental Cemetery (Pisa, Italy)

Aims: In this work, the ‘hi-tech’ complex biocleaning and restoration of the 14th-century fresco Triumph of Death (5·6 × 15·0 m) at the Camposanto Monumental Cemetery (Pisa, Italy) is reported. Since 2000, the restoration based on the biological cleaning of noble medieval frescoes, has been successfully utilized in this site. Methods and Results: The novelty of this study is the two-steps biocleaning process using Pseudomonas stutzeri A29 viable cells, previously applied for recovering other valuable frescoes. In this case, after the fresco detachment from the asbestos-cement support (eternity), both the animal glue and the residues of calcium caseinate were biologically removed respectively from the front and from the back of the fresco in 3 h as indicated by GC-MS and PY/GC-MS analyses. The data obtained during the monitoring of the biorestoration process confirmed that the adopted procedure does not leave residual cells on the fresco surfaces as showed by plate count method, ATP determination and also SEM observation. In addition, to avoid the risk of condensation phenomena after the relocation of the restored fresco sections onto the original walls, the use of a new support has been set up together with the design of a control system that allows a continuous monitoring of environmental parameters for prevention and conservation purposes. Conclusions: This large-scale biorestoration work clearly shows and confirms that this biotechnology is highly efficient, safe, noninvasive, risk-free and very competitive compared to the traditional cleaning methods, offering an unusual ‘resurrection’ of the degraded artworks also in very complicated and delicate conditions such as the Triumph of Death fresco, defined for its dimension and artistic importance the ‘Pisa's Sistina frescoes’. Significance and Impact of the Study: These findings can be of significant importance for other future new restoration activities and they are crucial for determining preservation strategies in this field.