The chrome plating of the Terracotta Army bronze weapons, once thought to be the oldest form of anti-oxidation technology, is derived from a decorative varnish instead of a preservation technique, a new study finds. led by researchers from UCL and Terracotta Army Museum.
The study, published today in. Scientific reports, reveals that the chemical composition and characteristics of the surrounding soil, instead of chromium, may be responsible for the famous power of conservation of weapons.
The main author, Professor Marcos Martinón-Torres (University of Cambridge and formerly of the Institute of Archeology of the UCL), commented: "The terracotta warriors and most of the organic materials of the mausoleum were covered with protective layers of lacquer before paint them with pigments, but curiously, no 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 chromium traces found in the bronzes are always in the parts of weapons directly badociated with organic elements now in decay, such as spear axes and wooden sword hilts and bamboo, which would also have had a coating of lacquer Clearly, lacquer is the unwanted source of chromium in bronzes, and not an old anticorrosive treatment "
The world-famous Terracotta Army of Xi & an is made up of thousands of life-size ceramic figures representing warriors, stationed in three large pits inside 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, spears, hooks, swords, crossbow triggers and up to 40,000 arrowheads have been recovered. Although the original organic components of weapons, such as wooden axles, quivers and pods, have mostly deteriorated over the past 2,000 years, the bronze components remain in very good condition.
Since the first excavations of the Terracotta Army in the 1970s, researchers have suggested that the impeccable state of conservation observed in bronze weapons should be the result of Qin's weapons manufacturers have developed a unique method for Prevent metal corrosion.
Chromium traces detected on the surface of bronze weapons gave rise to the belief that Qin artisans invented a precedent to chromate conversion coating technology, a technique patented only at the beginning of the 20th century and still use today. History has been cited in some books and media.
Now, an international team of researchers shows that the chromium found in bronze surfaces is simply a contamination of lacquer present in adjacent objects, and is not the result of an old technology. The researchers also suggest that the excellent conservation of bronze weapons may have been helped by the moderately alkaline pH, the small particle size and the low organic content of the surrounding soil.
Dr. Xiuzhen Li (Institute of Archeology of the UCL and Terracotta Army Museum), co-author of the study, said: "Some of the bronze weapons, particular swords, spears and halberds, show almost pristine bright surfaces and sharp blades after 2,000 years buried with the Terracotta Army, one hypothesis for this was that the Qin weapons manufacturers could have used some kind of anticorrosive technology due to the chromium detected on the surface of the weapons, however, the preservation of the weapons has perplexed scientists for more than forty years.
"The bronze composition of tin, the technique of extinction and the particular nature of the local soil somehow explain its remarkable conservation, but it is still possible that the Qin Dynasty has developed a mysterious technological process and this deserves more investigation."
By badyzing hundreds of artifacts, the researchers also found that many of the best-preserved bronze weapons did not have any chromium surface. To investigate the reasons for their excellent preservation, they simulated the weathering of the replicas of the bronzes in an environmental chamber. The bronzes buried in Xi'an's soil remained almost pristine after four months of extreme temperature and humidity, in contrast to the severe corrosion of buried bronzes for comparison on British soil.
"It is surprising the amount of important and detailed information that can be recovered through the evidence of both natural materials and the complex artificial recipes found in the mausoleum complex: bronze, clay, wood, lacquer and pigments, among These materials are complementary. "A larger story of craft production strategies at the dawn of China's first empire," said co-author Professor Andrew Bevan (Institute of Archeology, UCL).
Professor Thilo Rehren (Institute of Cyprus and Institute of Archeology of the UCL) stressed the importance of long-term collaboration. "We started this research more than 10 years ago between UCL and the museum, and only through persistence, trusting cooperation and the immediate thinking of colleagues in China and Great Britain could we solve this mystery of a decade."
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The chromium on the surface of the bronze weapons of the Terracotta Army is not an old anticorrosive treatment nor the reason for its good preservation. Scientific reports (2019). DOI: 10.1038 / s41598-019-40613-7, https://www.nature.com/articles/s41598-019-40613-7
Scientists shed light on the mystery of the preservation of weapons of the Terracotta Army (2019, April 4)
retrieved on April 4, 2019
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