Salt weathering of antique Dutch ceramic tiles

Salt crystallization poses a significant threat to cultural heritage. We focus on understanding salt weathering in antique Dutch tiles, a composite layered material composed of a clay body and a ceramic glaze. Physico-mechanical properties of those tiles were quantified. The role of salt nature and glaze configuration (intact and crazed) in the weathering process were visualized and compared during several wetting-drying cycles by using different techniques such as X-ray tomography, SEM imaging, and confocal profilometry. Physico-mechanical properties are found to be mostly alike for intact and crazed tiles. Both sodium chloride and sodium sulfate contamination lead to the accumulation of salt, but with different accumulation patterns. While sodium chloride precipitation can be found throughout the entire clay body, sodium sulfate precipitation accumulates near the interface between the glaze and the clay body at the corners where the evaporation is the highest. Subsequently, damage in the form of cracks crossing the clay body and the glaze leads to material detachment. Sodium sulfate is particularly damaging during the rewetting cycles prior to drying due to the formation of the hydrated phase mirabilite. Conservation treatments based on the use of liquid water should thus be avoided on sodium sulfate contaminated tiles.