Deterioration Phenomena And Conservation Methods of Stone Buddha Images In Japan

A word of stone cultural heritages recalls a stone Buddha image and/or a structure made of stone to our minds. Stone Buddha images, which were carved in rock mass, are one of the stone cultural heritages whose conservation and restoration works are difficult. Because stone Buddha images are usually in contact with the ground, they are affected by the underground water. Many stone Buddha images are seen in various parts of Japan, especially in Oita prefecture in Kyushu Island. There are about 400 stone Buddha images at 83 points in Oita prefecture (Oita City Board of Education 1996), and the Usuki Stone Buddha images (Photo I), which are distributed in the southeast of Oita prefecture, are the most famous among them (figure I). A group of the Usuki Buddha Stone Images was designated as a national important cultural property in 1962. Subsequently, it was also designated as a national treasure in 1995. The Usuki Stone Buddha Images have therefore two faces, i.e. cultural properties and arts. The Usuki Stone Buddha Images, which were sculptured in the later Heian period (in the 12th century), are mainly made of melted tuff formed by an ancient explosion of Mt. Aso. The degree of cementation of melted tuff is relatively small, and it is therefore not enough to strengthen the surface of rock mass, but necessary to reinforce from the side of structural mechanics of rock mass when melted tuff is weathered and deteriorated. Moreover, in case of conservation works, conservation methods should be investigated from every point of view as for the deteriorated stone Buddha images.

What is a stone Buddha image? First of all, we have to make clear as to what is a stone Buddha image. Nevertheless, it is difficult to define a stone Buddha image. A dictionary defines a stone Buddha image as a Buddha carved in stone, or a Buddha made of stone. Talking about stone, some stone Buddha images are sculptured in rock faces, and others are scraped in individual stones. In Japan, the first Buddha image was made in Nara period (in the 8th century). Consequently, the oldest stone Buddha images can be seen in Nara prefecture (Koushin Gathering for Friendly Discussion 1998). When the Heian period (between the late 8th and the late 12th century) came, many stone Buddha images were made all over the country. Excepting Shiga prefecture, there are few stone Buddha images in the former term of the Heian period. As Usuki, Kumano and so on were made numerously in Oita prefecture, and present grand sights. There are also some other stone Buddha images in Toyama and Tochigi prefecture.