ADVANCED MATERIALS & PROCESSES | JULY 2026 34 silicone coating could be applied to its surface. This treatment made it possible to display the object outdoors under severe environmental conditions, such as snowfall, rainwater exposure, freezethaw cycles, and significant temperature fluctuations, while preserving the original texture and color tone of the stone surface. The effectiveness of silicone-based inorganic coatings in such applications is closely related to their unique molecular structure and to their interaction with porous mineral materials. Welded tuff contains numerous microscopic pores and pathways that allow water to penetrate into the interior of the stone. Once moisture enters these porous structures, repeated freezing and thawing may generate internal stress. As a result, cracking, surface exfoliation, and gradual deterioration may occur. Alkoxysilane-based materials can penetrate deeply into these fine pore structures because of their low viscosity before curing. After penetration, hydrolysis and condensation reactions take place within the stone. They form a siloxane (Si–O–Si) network both inside the porous structure and on the surface. As a result, the treated stone shows enhanced water repellency while still allowing trapped moisture to escape gradually. This combination of properties is collectively known as breathability. It is a fundamental difference from conventional acrylic and urethane coatings, which tend to form dense, near-impermeable organic films. From the practical viewpoint, this balance is particularly important in cultural heritage conservation. This is because the excessive sealing of stone surfaces may accelerate internal deterioration through freeze-thaw cycles or salt crystallization. Another advantage of silicone- derived inorganic coatings is that they generally preserve the natural appearance of stone materials. Unlike thick organic paint films, these treatments form extremely thin protective layers. Therefore, they do not significantly alter surface texture, gloss, or color. As a result, the visual and tactile characteristics of historical stone objects can be maintained while improving environmental durability. OUTLOOK Looking to the future, there are further studies to be carried out. The authors plan to continue investigating the long-term behavior of alkoxysilane-derived coatings on heritage stone. For example, accelerated weathering tests, spectroscopic monitoring of the siloxane network, and depth-resolved analysis of resin penetration into porous lithologies are important issues in the next stage. Through these projects, the authors hope that conservators can choose the most suitable formulation for each heritage site, considering its specific mineralogy and microclimate. In this way, the application of materials science to cultural heritage will continue to develop further. These examples show how silicone- based inorganic coatings can contribute not only to modern industrial materials protection but also to the long-term preservation of cultural heritage and archaeological monuments exposed to harsh natural environments. ~AM&P For more information: Hideyuki Kanematsu, Specially Appointed Professor of Osaka University, Japan, and President & CEO of BEL (Biofilm Engineering Laboratory) Inc., +81.90.8499.6124, h.kanematsu@mat. eng.osaka-u.ac.jp. Fig. 2 — The Kitazawa Sekibō and the application of silicone coating to the monument: (a) overall appearance; and (b) the coating shop. Courtesy of D&D K.K. (b) (a)
RkJQdWJsaXNoZXIy MTYyMzk3NQ==