Estimation of the Alkaline Reserve of Calcite-Based Nanoparticles over Time Using Machine Learning for Benchmark Recognition on Historical Substrates

Over the last few decades, colloid and materials science has provided a range of tools for the cleaning, consolidation, and pH control of artistic and historical substrates. Nanostructured materials, such as microemulsions, micellar solutions, dispersions of alkaline nanoparticles, and chemical gels, are used to effectively counteract degradation processes without altering the physicochemical properties of the treated artworks, while minimizing or completely avoiding potential drawbacks. Here, a methodology to estimate the long-term stability of nanoparticles (NPs) is presented as a function of pH stability control and treatment durability over time. Specifically, the effects of Ca(OH)₂ nanoparticle deposition are estimated by extracting spectroscopic benchmarks attributed to the successive formation of CaCO₃ (vaterite), which is monitored using the kernel density estimation (KDE) algorithm and absorbance ratio. Different application methodologies are tested as deacidification procedures. The alkaline reserve of the formulated nanoparticles (NPs) is tested on a theatrical manuscript (dated back to the 15th century). The results explore the current challenges and potential breakthroughs in developing procedures to establish the durability of calcite-based NPs for conservative applications. They provide a reference procedure for researchers working on applied treatments in field applications. These findings demonstrate that nanoparticle behavior is both material- and method-dependent, with the adhesive application ensuring greater long-term uniformity and buffering stability compared with the spray method, which introduces higher variability. The data indicate that nanoparticle deposition becomes more homogeneous over time, particularly in more acidic regions, suggesting enhanced reactivity. Furthermore, the shift toward higher pH values over time supports the effectiveness of the applied treatments in achieving consistent pH neutralization. These results underscore the importance of optimized application techniques for the reliable, long-term preservation of historical libraries and archives.