Rb-Sr whole-rock and mineral isochron ages of the Otagiri granites from the Ina district, Ryoke belt, Southwest Japan Arc.

Abstract

The St. Xavier Chapel built in 1890, Kyoto, Japan, was moved to the Museum Meiji-Mura in 1965. In the Chapel, there are fourteen oil paintings called “Via Crucis” painted on metal plate. Among them, ten works have been restored since 1989. During restoration, paint fragments were sampled and researched by mineralogical methods: observation of cross-sections by an optical microscope, and identification of pigments by EPMA. Main materials of the white ground layer are barite (Ba0.96Sr0.04) SO4 and hyrdocerrusite. In the painting layer, hydrocerrucite was also used as a white pigment. For the other colors, hematite, goethite, illite, ultramarine blue (lazurite), vermillion (cinnabar) and carbon and ivory black were found. The hydrocerrusite, ultramarine, vermillion and carbon and ivory black are considered as synthetic pigments. Between the white ground layer and the metal plate, a green transparent oil layer containing copper and zinc was observed. This layer may be formed as a result of a chemical reaction between the oil and the metal plate. Based on the ratio of copper and zinc, the metal plate is considered as of a brass. Before the restoration, the surface of the works appeared pale green to the naked eye. There are two possibilities for the reason: one is the migration of green oil to the surface and the other is the glazing effect of the yellowing varnish and the black pigments having alittle blue color.