Advanced ultrasonic diagnostics for restoration: effectiveness of natural consolidants on painted surfaces

This study presents the first application of an automatic ultrasonic mapping system for the assessment of natural consolidants applied to replicas of painted wall surfaces. In Cultural Heritage conservation, evaluating consolidation efficiency remains a critical issue, particularly for substrates characterized by high porosity, heterogeneity, and mechanical fragility. Ultrasonic testing offers a fully non-contact diagnostic approach capable of detecting variations in cohesion, stiffness, and internal discontinuities, thus overcoming the limitations of semi-invasive mechanical procedures. Three polysaccharide-based consolidants—Arabic gum, Funori, and Opuntia ficus-indica mucilage—were applied to wall-painting replicas prepared according to historically documented techniques. Their performance was investigated through a comparative methodology combining a peeling test with non-contact air-coupled ultrasonic probes. Results indicate that Opuntia mucilage, although still at an experimental stage, provides significant improvements in cohesion, confirming its potential as a sustainable and substrate-compatible alternative to conventional consolidants. By demonstrating the complementary nature of ultrasonic mapping and peeling tests, this work contributes to the development of reproducible, non-invasive diagnostic strategies for evaluating consolidation treatments, particularly on fragile surfaces where conventional mechanical testing is unsuitable.