Sol–gel coatings in the ZrO2–SiO2 system for protection of historical works of glass

Different kinds of protective treatments based on sol–gel coatings have been designed and prepared. Final application of these coatings would be used for protection and preventive conservation of a wide variety of historical glasses from several times and provenance. Historical glasses show a superficial deterioration depending on the exhibition conditions submitted by the ancient objects since their origin. The coatings effectiveness was confirmed by means of accelerated ageing tests under simulated atmospheric polluted conditions by using SO2 as a pollutant and different kind of glasses as reference substrates. Coatings with compositions 100SiO2 and 10ZrO2·90SiO2 (mol%) proved to be highly protective when they were densified up to 250 and 400 °C for 1 h. Those coatings densified at lower temperature (for instance, 60 °C for 3 days) appeared partially cracked and detached after the ageing tests. For compositions 50ZrO2·50SiO2 and 100ZrO2 the major problem was concerned to the high surface reflectance provided by the zirconium oxide, which modifies very much the appearance of the substrate glasses.