InCare project: narrowing the gap between laboratory studies and conservation practice

The PRIN 2022-InCARE project aims to establish a comprehensive methodology for protecting metal artefacts from corrosion using a chemometric approach. Initially, two non-toxic corrosion inhibitors and two light stabilizers were added to Paraloid B44 and the best-performing formulations for testing were identified after artificial solar ageing. Following this, a detailed non-destructive multi-analytical characterization of 161 bronze “Verde Messina” patinated mock-ups was conducted. This included colorimetry, thickness measurements, electrochemical impedance spectroscopy (EIS), and Fourier Transform Infrared Spectroscopy (FTIR). The patina primarily consisted of rouaite (Cu2(NO3)(OH)3) and did not possess protective properties. Using principal component analysis (PCA) mock-up outliers were identified and the distribution of surface properties on the samples was characterised. Different application methods of the selected acrylic formulations on the bronze specimens were evaluated. Two layers were applied by brush one week apart, both at 10 percent w/w of Paraloid B44 in 1-methoxypropan-2-ol or with a more diluted first layer (5 percent w/w). These were characterized before and after thermo-hygrometric artificial ageing. The results indicated that the most effective application method involved using a Paraloid concentration of 5 percent w/w for the first layer and 10 percent w/w for the second layer. This approach provided enhanced protection, as evidenced by higher polarization resistance (Rp) values, while keeping the same thickness and colour changes. Additionally, the formulations containing the inhibitor 5-ethyl-1,3,4-thiadiazol-2-amine (AEDTA) offered increased protection. PCA of the FTIR data confirmed that the most effective coatings were those with the lowest concentration of acrylic resin as a first layer. This application method was adopted for mock-ups to compare the effectiveness of the selected formulations with additive free Paraloid B44 and Incralac, which are currently undergoing weathering in a marine-industrial environment.