The study of change in chemical conpositious of ancient glasses found in Eastern Asia.

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The study of the change in chemical compositions of ancient glasses found in Japan as well as the comparison of the obtained results with that of China and Korea is one of the important subjects to understand the influence of these foreign countries on Japanese glass-producing technique.The glass samples (mainly glass beads) were collected from about fifty archaeological sites in Japan, covering periods from 2nd century B.C.to the end of the 8th century A.D.The quantitative analysis of more than eight hundred glass samples were mainly performed by using a micro-focused energy dispersive X-ray fluorescence spectrometry with FP method. Besides, the inductive coupled plasma emission spectrometry and the atomic absorption spectrometry were also used for some samples.The corrosion products and the weathering surface layrs of glass samples were preliminary removed from the small examining area for the analysis.The lead isotope ratio of some glasses found in Japan were also measured. The data have been cross-checked with that of glasses or lead ores in China and Korea, known to have been produced in the past.Our results clarified the following facts :1) The distinctive glass systems at periods from ca.2nd century B.C.to the 3rd century A.D.were K_2O-SiO_2, PbO-BaO-SiO_2 and PbO-SiO_2. Two systems of soda-lime glass (Na_2-CaO-SiO_2 and Na_2O-Al_2O_3-CaO-SiO_2) appeared after the late 3rd century A.D., whereas two systems of before-mentioned lead glass disappeared. The PbO-SiO_2 system reappeared since the late 6th century, and produced in Japan for the first time.2) Many glass producing relics (dated as the end of 7th century) were excavated at the lead-glass producing site found for the first time in Japan. The results of our analysis showed that these glasses were the first lead-glass produced in Japan.