35 JEOL News Vol. 49 No. 1 (2014) Electron Microprobe Study of the Yinxu (Anyang) Bronze of Academia Sinica Collection Yoshiyuki Iizuka 1 and Junko Uchida 2 1 Institute of Earth Sciences, and 2 Institute of History and Philology, Academia Sinica To understand bronze casting technology in ancient China, a series of electron microprobe study has been carried out on bronze objects from the Yinxu (Anyang) in the Academia Sinica collection. Because oxidation parts of bronzes do not preserve the original structures and chemical compositions, non damaged bronze’s interior in polished cross-sections were carefully selected, and then their micro-structure and chemical compositions were investigated. Observed metallurgical structures of bronze are divided in two types; dendrite and granular (annealed) structures. Although the granular structured bronze is not common, it suggests that the heat treatment technique has already been applied in the Yinxu Period. Oxygen was also measured to conirm its condition of the oxidation by EPMA, and 73 samples of arms and vessels were discriminated as well-preserved samples. Most of the Yinxu bronzes are tin (Sn)-bronze with a little amount of lead (Pb). An overall result indicates that the bulk Cu/(Cu+Sn) ratios of the bronzes range from 0.79 to 0.89, and chemical compositions are rather different in type of usages. It indicates that the chemical compositions (mixture ratios of Cu:Sn) of the bronzes were already intentionally controlled for their usages in the Yinxu Period. Introduction Institute of History and Philology, Academia Sinica, which was established in 1928 for modern archaeological studies, performed excavation works for 15 times in Yinxu ( 殷墟 ) of Anyang, Henan Province, the Central Plain in China. Excavation programs were suspended in 1937 due to chaotic situations. The most of excavated materials were transferred, and a large quantity of bronze objects from Yinxu has been stored in the Institute since 1949, now at Taipei. Yinxu is the place where the oracle bone scripts were discovered and is thought to be an ancient capital in the Late Shang Dynasty (ca . 14c.BC-11c.BC), in the Bronze Age of China. The Yinxu bronzes of the Academia Sinica collection were excavated from aristocratic tombs in the Xiaotun palace area, and royal tombs in the Xibeigang area and the collection contains all kinds of bronze objects from all phases of time sequences through the Yinxu Period. Although the collection is one of the most precious and variable for study of the Bronze culture, only little amount of bronze was studied by scientific approaches. To understand technological innovation of bronze casting in the East Asia, the Yinxu's materials are extremely important because it used to be the center of bronze manufacture at early Bronze Age in the East Asia. Information from the Yinxu bronzes and further comparison study of other ages, areas and technology would indicate evolution of the Bronze culture. Since 2007, the authors have launched a series of investigation of the Yinxu bronze collection using electron microprobe techniques to reveal bronze casting technology in Anyang of the Shang Dynasty. Here we report on analytical methods of ancient bronze and implications of bronze culture in the Shang Dynasty. Ancient bronzes and sample preparations The bronze, the first alloy of human kind, is composed of two metallic elements of copper (Cu) and tin (Sn). Bronze object was manufactured by pouring molten alloy into a mold. Melting points of Cu and Sn are approx. 1085ºC and 232ºC, respectively, and melting points decrease with increasing of Sn content in bronze. Figure 1a shows the phase diagram of Cu- Sn (tin-bronze) system. Of molten bonze within 90- 80 wt.% of Cu (10-20 wt.% of Sn), the primary solid phase of bronze is α-phase when it reached the liquidus temperature. The α -phase generates segregation- solidification (dendrite: Fig. 1b-d) during temperature falling and then secondary δ-phase appears in cooling rate of normal casting. In normal casting, crystallization of Sn-enriched phases, ε and η, does not occur because temperature falls too low to react. In other words, only No. 128, Sec. 2, Academia Road, Nangang, Taipei, Taiwan E-mail: yiizuka@earth.sinica.edu.tw