PVA–Borax Double-Network Gels for Sustainable and Selective Cleaning of Highly Textured Street and Urban Murals

The removal of spray paint vandalism from contemporary mural paintings and Street and Urban Art represents one of the most challenging operations in conservation practice, particularly when the unwanted layers are chemically similar to the original pictorial materials. Conventional cleaning methodologies often show limitations on rough and heterogeneous surfaces, where the risk of irreversible alteration of the original paint film increases. This study proposes tunable cleaning systems based on polyvinyl alcohol (PVA)–borax double-network hydrogels modified with biopolymers and loaded with nanostructured fluids for controlled and sustainable removal of spray-paint vandalism. Laboratory investigations, including solubility tests, qualitative assessment of mechanical properties and cleaning trials on representative mock-ups, were carried out to evaluate the stability, adaptability and cleaning performance of the most promising systems, including laboratory-prepared PVA-based formulations and commercial Peggy Nanorestore gels©. The optimized cleaning systems were successfully applied in situ on the mural Nido di Vespe in Rome, achieving a controlled reduction of the vandalism layer while preserving the integrity of the original surface and confirming the applicability of these systems under real conservation conditions.