Comparison study between new green coating and benchmark products for the protection of frescoed surfaces

This study reports the assessment of a new green coating for the protection of frescoes exposed outdoor, combining the antimicrobial and antifungal activities of chitosan biopolymer with the bacteriostatic and hydrophobic features of silver nanoparticles (Ag+ NPs) [1,2]. The protective surface properties of the new formulation were compared with those of commercial products (i.e. Paraloid B72 ® and Proconsol ®) used by restorers for consolidation and protection interventions on wall paintings and stone materials. The coatings have been tested on ad hoc prepared mock-ups, investigating chemical and colorimetric stability, hydrophobicity, water vapor permeability and surface morphological variations, before and after artificial ageing. Since the conservation environment is closely related to the conservation conditions of frescoes, the multi-analytical methodology and the ageing protocol (i.e. temperature, light irradiation and rainfall simulation) of this study were developed specifically, starting from the conservation conditions of the archaeological site of Aquileia, considered as a case study. The results of this comparative work demonstrated that the new green coating gives the frescoed surface a good hydrophobicity and permeability to water vapor. These are important characteristics for guaranteeing the breathing of the wall and for avoiding stagnant water, and thus trigger further forms of degradation [3]. Furthermore, compared to the commonly used Paraloid B72 ® and Proconsol ®, the new formulation showed a limited variation of color, it did not make the surface glossy, and a good chemical stability after artificial ageing, as demonstrated by the lack of chemical modifications in the FTIR-ATR spectrum. The developed formulation is promising for the protection of frescoes exposed outdoor and for minimizing the progression of surface degradation. The antimicrobial and antifungal properties of the excipients will be tested in future studies, in order to provide a complete overview on the new formulation.