中国後漢代青銅鏡の土中腐食層内で観察された結晶学的特異現象

Abstract

Recently, we have got a chance to collect a small piece of the ancient bronze mirror, which had been manufactured in the middle or the late Chinese Han period. To investigate it’s metallurgical properties by means of optical microstructure observation and various instrumental analyses. From these investigations, we have detected the crystalline anomalies in the corroded layer alias “bronze disease” layer in the clay for the ancient bronze mirror. Results obtained were as follows:(1) The apparent density of the mirror, measured by means of the Archimedes method, tends to decrease with the extent of the corroded layer in the clay.(2) The semi-transparent thin film formed on the mirror was the crystalline tin oxide (SnO2).(3) The corroded structural defect alias “bronze disease” layer formed just under the surface of mirror was the amorphous (like) tin oxide, which contains lower Cu and higher Pb contents.(4) Mechanisms of the formations of the semi transparent thin film on the mirror surface and the amorphous (like) layer in the attacked layer in the clay and the behavior of the copper element should be made clear hereafter.