2018 Volume 82 Issue 8 Pages 319-325
The Takamatsuzuka tumulus was constructed in the 7-8th centuries at Asuka in the current Nara Prefecture. The mural is painted on the stucco plastered over the tuff wall. The stucco is apparently rough due to degradation, and therefore, the mural surface is also rough. The purpose of this research is to clarify the causative factor of the degradation observed in the stucco materials scientifically. Surface and inner morphology of the stucco are observed using a computerized X-ray tomograph (CT), a scanning electron microscope, and a transmission electron microscope. Impurity elements are analyzed by means of energy dispersive X-ray spectroscopy. Many tunnel-like voids are observed in the stucco. Two-dimensional macroscopic-void areas observed by CT account for approximately 15 percent of the total area. Furthermore, a great many voids in micrometer-size are observed. Numerous small CaCO3 crystals grow from the tunnel wall, and impurity content of the grown crystal is lower than that of the stucco matrix. This shows that the grown crystal is purified in the process of recrystallization. It is thought that the tunnel is formed by the dissolution of stucco constituents into water during the wet season. Then the small crystals grow by recrystallization from water containing stucco constituents during the dry season.
