For decades, scientists have been perplexed by the marvelous preservation of bronze weapons associated with China’s famed Terracotta Warriors, retaining shiny, almost pristine surfaces and sharp blades after being buried for more than two millennia. Research by an international team of scientists published on April 4 may solve the mystery while putting to rest an intriguing hypothesis: that ancient Chinese artisans employed an unexpectedly advanced preservation method using the metal chromium.
The fine preservation of weapons including swords, lances and halberds was due to serendipity — factors such as the bronze’s high tin content and favorable soil composition — the scientists decided after examining 464 bronze weapons and parts. Chromium found on the bronze surfaces, they determined, was simply contamination from chromium-rich lacquer applied by the artisans to the terracotta figures and weapons parts. Chromium played no role in their preservation.
The Terracotta Army consists of thousands of life-sized ceramic warriors and horses alongside bronze chariots and weapons, part of the vast 3rd century BC mausoleum near the city of Xian for Qin Shi Huang, first emperor of a unified China. Found in 1974, it represents one of the 20th century’s greatest archaeological discoveries. Scientific analyses almost four decades ago detected chromium on the surface of some of the weapons, spurring the hypothesis that the weapon-makers used a chromium-based treatment to prevent corrosion.
Photo: REUTERS
照片：路透
Chromium-conversion coating, a technology discovered in the early 20th century, is used to treat metals to render them more corrosion resistant. It involves dipping metal in a solution containing chromium salts. A chromium oxide layer is deposited on the metal’s surface, providing a barrier against rust.
“The lacquer was applied to the Terracotta Army as a primer before they were painted with colors, and we think it’s quite likely it was also applied to the now-decayed wooden parts such as handles and shafts,” said University of Cambridge archaeological scientist Marcos Martinon-Torres, who led the study published in the journal Scientific Reports.
Ancient bronzes often have poor states of preservation, with porous, pitted surfaces showing green or dark colors. “In essence, we show that, yes, the Terracotta Army weapons generally show a very good state of preservation, but there is currently no indication that this is anything other than the result of chance,” added Martinon-Torres, who participated in the research while at University College London and in collaboration with the Terracotta Army Museum.
(Reuters)
數十年來，科學家一直對於中國著名的兵馬俑深感困惑，難以解釋其青銅兵器不可思議的良好保存狀況，竟然在深埋地底超過兩千年後，表面仍然近似全新、閃閃發光，還保有銳利的刀鋒。一組國際科學家團隊於四月四日發表的研究或能解開這個謎團，並且讓一項吸引人的假說安心入土──該假說認為，古代中國工匠藉由運用鉻金屬，進行某種出人意料的先進保存方式。
在檢驗四百六十四件青銅器武器和部分物件後，科學家做出結論，指出包括劍、矛和戟等兵器保存狀態良好，其實是因為「一場美麗的意外」──例如青銅的高度錫含量，以及有利的土壤成份都是保存的要素。至於在青銅表面上發現的鉻，科學家則認定單純是富含鉻的亮光漆，因為工匠塗抹在赤陶人俑和武器上所造成的污染。對保存而言，鉻未起任何作用。
兵馬俑由數千個真人大小的陶瓷兵士和戰馬組成，配有青銅製的戰車和武器，是西安市近郊一處西元前三世紀大型陵墓的一部分，屬於首位統一中國的皇帝秦始皇。兵馬俑在一九七四年被發現，成為二十世紀最重大的考古發現之一。將近四十年前，科學分析在其中一些兵器的表面上偵測到鉻，引發假設，認為製造武器的工匠使用一種鉻為基底的保護膜來防止腐蝕。
鉻酸鹽轉化塗層是一項二十世紀早期發現的技術，被運用在金屬製品上，使其更能夠抗腐蝕。在製程中，會把金屬浸泡在內含鉻酸鹽的溶劑中，金屬表面就會附著一層氧化鉻，形成一道防止生鏽的護網。
這篇研究發表於期刊《科學報告》，由劍橋大學的考古科學家馬可斯‧馬提儂-托瑞主持，他表示：「亮光漆被塗在兵馬俑上作為底漆，之後再漆上不同顏色，而我們認為，亮光漆很有可能也被塗在今已腐朽的木造部位，例如握把或是箭桿上。」
遠古青銅器經常會有保存狀態不佳的情況，表面會變得多孔且凹凸不平，呈現綠色或其他暗色。馬提儂-托瑞目前於倫敦大學學院參與這項和秦始皇帝陵博物院合作的研究計畫，他補充表示：「總歸而言，我們證明出，沒錯，兵馬俑的兵器基本上呈現非常好的保存狀態，但目前沒有任何徵兆顯示這個現象可歸因於機運以外的其他可能性」。
（台北時報章厚明譯）
1. preservation n.
保存 (bao3 cun2)
2. bronze n.
青銅 (qing1 tong2)
3. serendipity n.
意外發現；機緣湊巧 (yi4 wai4 fa1 xian4; ji1 yuan2 cou4 qiao3)
4. Terracotta Army phr.
兵馬俑 (bing1 ma2 yong3)
5. coating n.
塗層；鍍膜 (tu2 ceng2; du4 mo2)
6. lacquer n.
亮光漆 (liang4 guang1 qi1)
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