Photopolymerizable golden-varnish in the ancient East-Asian countries, and KOSHIABURA of Japan

Abstract

Regarding the Koshiabura tree in ancient painting technology, many people have investigated its history but its material have not been made clear. KOSHIABURA was a mysterious problem among Japanese art technologists. In ancient times, it was significant that Japanese people usually thought that Koshiabura, Takanotsume and Kakuremino trees were the same, and these three were exactly the trees to make KOSHIABURA varnish for a tribute. We first reported on the chemical constituents of the KOSHIABURA varnishes made from resinous saps of Takanotsume, Japanese and Korean Kakuremino and Koshiabura trees, and found that they principally contained conjugated diyne compounds as the photopolymerizable monomers. These monomers easily polymerized under sunshine to form golden-colored, hardcoating films in a short time, and the films were waterproof and anticorrosive. In ancient times KOSHIABURA varnish in Japan was usually applied to paint armor suits, helmets, and arrowheads. The content of the diynes as the principal components were ca. 25% in Kakuremino, 30% in Takanotsume, and 2.8% in Koshiabura saps, respectively. In addition, we have found that the acetylenes of the Kakuremino tree have strong inhibitory activities against fungi. Therefore they are phytoalexins. As already known, these kinds of conjugated diynes are in the newest field of materials science. This paper contains general comments on the ancient photopolymerizable golden varnishes (KOSHIABURA varnishes in Japan) and their chemistry.