臺灣東部鐵器時代遺址出土玻璃珠之科學檢測

臺灣大約在2500-2000年前開始進入所謂的鐵器時代，部分日常使用的石器逐漸為金屬材料製品所取代，此外玻璃製品也廣泛出現在遺址的出土文物中。除了火山玻璃外，大部分的玻璃都是人造製品，古人利用助熔劑在1000度以上的高溫將石英質材料熔融後製成，因此從出土玻璃文物的化學組成分析可以了解玻璃的製造過程，甚至可以了解玻璃原料的來源地，對於解釋古人的工藝技術或是貿易/交換體系可以提供必要的科學證據。本文將就國立臺灣史前文化博物館受委託或自行研究發掘的4個臺灣東部鐵器時代遺址（分別位於花蓮縣壽豐鄉之平林遺址，臺東縣卑南遺址、舊香蘭遺址及多良遺址）出土之玻璃珠進行之初步科學分析。四個遺址的文化層年代都屬於鐵器時代早期，除舊香蘭遺址曾有多彩玻璃珠的出土，大部分玻璃珠都是臺灣鐵器時代遺址常見的單色印度-太平洋珠，常見的有藍珠、綠珠、黃珠、紅珠、橘色珠等顏色，平林遺址出現少見的紫色珠。不同遺址出土的玻璃珠數量差距頗大，有些遺址出土數千顆甚至上萬顆的玻璃珠，有些遺址可能只發現幾顆玻璃珠，基於出土玻璃珠的稀有性，本研究以非破壞性的掃描式電子顯微鏡配合能量光譜分析方法進行初步研究。分析結果顯示，位於縱谷及臺東平原的平林遺址及卑南遺址，出土的玻璃珠屬於鉀玻璃系統，而伴隨有龜山式陶片出土的舊香蘭及多良遺址的玻璃珠，卻屬於印度-太平洋珠中最常見的鈉玻璃系統。從兩種玻璃系統中氧化鋁含量的差別，可以了解兩種玻璃珠的石英砂原料應該來自不同的地質環境，製作舊香蘭及多良遺址玻璃珠的石英砂應該含有相當程度的黏土或長石礦物，而製作鉀玻璃的石英砂則相對純淨，其組成接近於地中海或中國南方製作的玻璃。在目前對南島語族社會的了解，玻璃珠有很長一段時間是珍貴而重要的交易物品，雖然現今對於玻璃珠的製造地和交換流通的管道並不甚清楚，但藉由出土玻璃珠科學分析資料的逐步累積，希望最終可以建構出一、二千年來，從史前到現代，玻璃珠在臺灣的交換與流動。

關鍵字

玻璃珠；鐵器時代；考古遺址；南島語族

並列摘要

The uses of metallic artifacts began 2500-2000 years ago in Taiwan; in the meanwhile glass beads have also been as a common ornament by the prehistoric people. Glass, as the earliest artificial ornament, is made by a mixture of quartz sands and flux which were heated to more than one thousand Celsius degrees. Therefore, the production processes, raw material provenance and exchange systems could be revealed by the chemical compositions of glass artifacts. The chemical composition of glass beads studies from four archaeological sites (Pinglin (PL) , Peinan (PN) , Chiuhsianlan (CHL) and Towlian (TL) site) in early Iron Age are reported in this study. Except 3 pieces of polychrome glass beads having been found in the Chiuhisanlan site, all the studied glass beads should be classified as Indo-Pacific glass beads which are produced by drawn methods and made in a limited range of colors with various hues: blue, green, yellow, red, violet and orange. The amounts of unearthed glass beads are greatly various from different site, such as glass beads from Chiuhsianlan site are tens of thousands but no more than sixty pieces of glass beads have been found in Pinglin site. As these ancient glass beads are unique and precious, a non-destructive analytical method is always considered at the initial stage. Therefore, we use the best known and most widely-used of the surface analytical techniques SEM/EDX (Image Scanning electron microscopy with energy dispersive X-ray spectroscopy) to get the surface and quantitative elemental information of glass beads. According to the SEM/EDX analytical results, glass beads excavated from the PL and PN sites all belong to potassium silica glass and those coexisting with so-called Kueishan sherds excavated from CHL and TL sites should be classified as sodium-calcium glass which is the most general composition of Indo-Pacific glass beads. Not only the different flux using between potassium and sodium glass, the variation in the aluminum contents between potassium and sodium glass also exhibits different provenances of glass-making raw materials. Glass beads had been widely used by many Austronesian indigenous groups from long time ago. Since glass-making technology was not developed locally, the ancient glass beads were considered as a precious and trading artifact to Taiwan from overseas and introduced into prehistoric societies via various sources and paths. Although the trading/exchange routes of ancient glass beads are still debatable, we find that compositional analyses can help answer such questions as what types of glass were used for their manufacture and with separate traditions and hope the results can give us some insight into the potential bead-making sites and in addition to establish the exchange networks of prehistoric people.