Republication from  sciencedaily.com

Photo credit: New York Times

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Source: University College London

The chrome plating on the Terracotta Army bronze weapons — once thought to be the earliest form of anti-rust technology — derives from a decorative varnish rather than a preservation technique, finds a new study co-led by UCL and Terracotta Army Museum researchers.

The study, published today in Scientific Reports, reveals that the chemical composition and characteristics of the surrounding soil, rather than chromium, may be responsible for the weapons’ famous preservation power.

Lead author Professor Marcos Martinón-Torres (University of Cambridge and formerly of UCL Institute of Archaeology), commented: “The terracotta warriors and most organic materials of the mausoleum were coated with protective layers of lacquer before being painted with pigments — but interestingly, not the bronze weapons.”

“We found a substantial chromium content in the lacquer, but only a trace of chromium in the nearby pigments and soil — possibly contamination. The highest traces of chromium found on bronzes are always on weapon parts directly associated to now-decayed organic elements, such as lance shafts and sword grips made of wood and bamboo, which would also have had a lacquer coating. Clearly, the lacquer is the unintended source of the chromium on the bronzes — and not an ancient anti-rust treatment.”

The world-famous Terracotta Army of Xi’an consists of thousands of life-sized ceramic figures representing warriors, stationed in three large pits within the mausoleum of Qin Shihuang (259-210 BC), the first emperor of a unified China.

These warriors were armed with fully functional bronze weapons; dozens of spears, lances, hooks, swords, crossbow triggers and as many as 40,000 arrow heads have all been recovered. Although the original organic components of the weapons such as the wooden shafts, quivers and scabbards have mostly decayed over the past 2,000 years, the bronze components remain in remarkably good condition.

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