Advancing preservation: a chemometric approach for monitoring the degradation of protective coatings for bronze statues

Bronze outdoor statues are often covered by a corrosion patina that forms due to environmental exposure, providing both aesthetic value and, partly, a surface passivation. However, this patina does not prevent from decay by external factors such as pollution, UV radiation, and humidity. To mitigate these decay processes, protective coatings are commonly used, but existing solutions often have drawbacks related to health, durability, and the need for frequent reapplication. The development of reliable, long-term conservation methods is essential. This work focuses on evaluating coatings formulated with Paraloid (R) B44, incorporating non-toxic corrosion inhibitors and light stabilizers. A total of twenty-one coatings were subjected to accelerated aging with artificial sunlight, and their decay was monitored using a multi-analytical approach involving Fourier Transform Infrared Spectroscopy (FT-IR) and UV-Vis spectroscopy, both with benchtop and portable spectrometers. The aim is to propose a method that combines spectroscopic data with chemometrics, specifically Principal Component Analysis (PCA), to objectively assess coating decay over time. The results demonstrate that PCA provides a simple yet powerful tool to distinguish between different formulations, track their aging, and rationalize decay processes. This approach not only facilitates the comparative analysis of coatings but also holds potential for field applications using portable instruments. By integrating spectroscopy with chemometrics, this method aligns with the principles of green analytical chemistry, offering a non-invasive, efficient means to monitor the effectiveness of protective coatings for cultural heritage preservation.