SPring-8, the large synchrotron radiation facility

Despite it is well known Sasanian glass^*1 in the Shosoin Tresure Repository, such as Hakururi no wan , a facet cut glass bowl, Ruri no Tsuki, a blue glass goblet, there is no clear definition of Sasanian glass. Fluorescent X-ray analysis^*2, by which trace elements contained in glassware are detected, is effective in identifying the method, date and place of manufacture of the glassware. This is because most of the trace elements contained in the glassware are heavy elements such as rare-earth elements, the contents of which largely differ depending on the area where the raw materials were obtained. The highly sensitive detection of heavy elements using high-energy X-rays gives a clue to the origin, namely, the place and date of manufacture, of the glassware.

SPring-8^*3 is a high-energy synchrotron radiation source that produces high-energy X-rays and enables highly sensitive measurement of all elements including uranium. Using the high-energy X-rays of SPring-8, Ryuji Shikaku (assistant chief curator) of the Okayama Orient Museum (Director, Toshiaki Otsuka), Izumi Nakai (professor) and Yoshinari Abe (assistant professor) of the Tokyo University of Science (Chairman of the Board of Directors, Shigeru Nakane), and Naoto Yagi (coordinator), Yoshiharu Sakurai (group leader) and Masayoshi Ito (research scientist) of JASRI (President, Yoshiharu Doi) developed a technique for analyzing glassware in a nondestructive manner. This new technique enables the measurement of valuable archaeological materials and museum pieces without damaging them and will be applied to the cultural research of ancient glassware in the future.

The Okayama Orient Museum provided the materials examined in this research. The featured materials were the glassware including sherds, manufactured during the Sassanian dynasty in the period from 226 to 651 AD. The analysis at SPring-8 revealed that a large amount of heavy elements, such as rare-earth elements, is contained in the “Bowl with Pinched Decoration”, which is identified as early Sassanian glassware manufactured from the 3rd to 4th centuries on the basis of typological features. On the other hand, only a small amount of heavy elements is contained in the “Circular Facetted Bowl”, which is identified as late Sassanian glassware manufactured during the 6th to 7th centuries. Such a compositional difference reflects the difference in the raw materials of these vessels. The results of this experiment show the possibility of estimating the date of manufacture of Sassanian glassware in a nondestructive manner.

In this research, the state-of-the-art technique of synchrotron radiation analysis was used to deepen the understanding of the Shosoin Treasures, namely, to solve the mysteries of cultural assets. The results of this research make the significance and usefulness of synchrotron radiation science understandable and realistic to everyone and show that the utilization of synchrotron radiation supports a wide range of academic research. The achievements will be presented at academic conferences. In addition, many artworks and archaeological artifacts that belong to our museums will be examined and better understood using not only the fluorescent X-ray analysis but also the high-resolution X-ray imaging and high-precision X-ray diffraction at SPring-8.