A “double” EIS study: Early corrosion diagnosis and testing of a new waste-polystyrene-based coating against the bronze disease

In the conservation of Cultural Heritage, bronze disease — an aggressive and destructive form of copper alloy corrosion induced by chlorides — remains a major challenge, as it is often detected only at an advanced stage, when intervention becomes difficult. This study employed potentiostatic Electrochemical Impedance Spectroscopy (EIS) measurements on two sets of bronze samples to assess the feasibility of early detection of bronze disease (which is invisible to the naked eye and undetectable with most portable instruments) and to evaluate a novel coating based on upcycled polystyrene (PS-MA). Since bronze artworks often require in situ characterization, and given the delicate nature of their surfaces, minimizing contact between the bronze and electrolyte during EIS measurements is essential. To simulate outdoor conditions, coated bronze mockups were analyzed using a gel polymer electrolyte (G-PE). EIS analysis yielded valuable insights into the electrochemical behavior of the system and assessed the protective efficacy of the synthesized coatings. Additionally, Spectral-Domain Optical Coherence Tomography (SD-OCT) was employed to examine coating adhesion and thickness on the bronze surface.