法隆寺金堂壁画の顔料及びその火災による変化について

The walls of the Main Hall consist of four large units (each 10 x 8.5 feet) and eight smaller ones (each 10 x 5 feet). The walls are made of mixture of clay, sand and straw bits as binders. The surface of the wall is coated with thin layer of clay upon which are painted the figures of Buddhas and Bodhi-sattvas with so-called “mineral pigments.” The pigments were studied chemically before and after the fire of January 1949. They are listed in Table 1. * Calcium carbonate which was used at the time of repair on the edges of the walls changed by the fire to calcium oxide and then to calcium hydroxide by absorbing water. The surface layer of the walls made of clay showed the same change as that of earthen wares by the fire. It lost water and changed to a kind of biscuit. The changes of the pigments caused by the fire are summarized in Table 1. The predominant green and red colours of the paintings were lost and they changed nearly to black and white, that is, black colour of cupric oxide remained on the white ground of clay. Only the red colour of iron oxide red is observed in several places of the walls. The left half of the large wall of the north-east corner of the Main Hall (the wall no. 10) showed a different aspect from other walls. It was covered with the reducing flame during the fire as shown in the Photograph. The reduction of the pigments occurred. Red lead and litharge were reduced to grey metallic lead, and green malachite and blue azurite changed to reddish brown cuprous oxide. Carbon also deposited in this reduction zone. By the fire litharge used as the pigment melted, while the copper wire used in the Main Hall remained unchanged. From these facts the temperature of the walls during the fire is supposed to have been between the melting temperature of copper and litharge, that is, 1083° and 880° respectively.