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(Credit: lapas77 / Shutterstock)
To protect the Chinese emperor Qin Shihuang in the afterlife, thousands of clay soldiers joined him underground about 2,200 years ago. The discovery of this terracotta army in the 1970s was a great gift for archaeologists – and fans of "old lost technology" stories. The trope, which actually has a basis, suggests that our ancestors were aware of certain knowledge or technologies that would still be useful, but have since been lost.
When the researchers discovered that this ancient buried clay army possessed remarkably preserved weapons, it was reasonable to wonder if the craftsmen of the time had treated them to prevent rust. Chemical analyzes showed that the arms contained traces of the chromium element, an ingredient in stainless steel, and for decades it has been thought that the Qin population has developed a chrome-based cold rust-free coating for arm them.
Well, a new search appearing today in Scientific reports shows that … maybe not so much. The international team of authors writes that "the theory of rustproofing chromium treatment should be abandoned". The reasoning is simple: chromium appeared only in a few weapons, had little to do with actual conservation and was probably related to a different and explainable process. Instead, the authors suggest some possible reasons for preserving the weapon that have real evidence behind them.
Terracotta techniques
The authors certainly did not lack artifacts from which to choose. Archaeologists have recovered dozens of bronze spears, spears, swords, hooks and thousands of arrowheads of life-size terracotta warriors. And early research suggested that a "chromate conversion coating" (CCC) applied by Qin craftsmen could indeed explain the remarkable preservation of weapons. But previous studies had already begun to question the idea, even if the results were not conclusive, and the current conclusions are based on the CCC hypothesis by carefully examining the distribution of chromium between and in the old arms. .
Detail of the handle and blade of one of the Terracotta army swords. In most of the swords analyzed, the highest concentrations of chromium are detected in the guard and other accessories that would have been in contact with the lacquered organic parts. (Credit: Zhao Zhen)
First of all, it turned out that chromium was not even so prevalent. It only appears in 37 of the 464 weapon samples the team has studied – this is not the type of widespread use you expect from deliberate reinforcement treatment. And the analysis also revealed an even greater reason to be wary of the CCC theory: the best-preserved weapons were not even those with the most chromium, and vice versa. "There is no correlation between the presence of chromium and the state of conservation of a given weapon," write the authors.
So why is there chrome on the terracotta warrior's weapons? After ruling out possible sources such as the metal ores used to make the weapons, the pigments used to decorate them and the soil contamination itself, the researchers turned to the distribution of the element in the weapons they -Same. They found that it was generally limited to areas near the knobs, handles and triggers, usually made of wood and lacquered. At the time, the treatment was used in China and the team showed that it would contain chromium in sufficient quantity to explain the quantities still detectable on the weapons – but only the parts close to the application of the lacquer.
All answers
We know now why the weapons contained chromium, but what about the other big question: why are they so well preserved? The authors also have an answer to this, suggesting that it is a combination of the higher tin content of bronze (which avoids corrosion) and the special soil in which the Terracotta army was buried. showed that its slightly alkaline chemical composition and relatively small particle size would prevent natural acids and organic matter from gnawing metals.
"In conclusion," the authors boast, "the bewildering suggestion that Qin weapon manufacturers have used arcane chrome-based technology to prevent rust from weapons has been refuted." Efforts should be made to put day information from museum sites and popular literature on the site. "
Of course, it's a little disappointing that the Terracotta Army is not a good example of the lost technology of an ancient civilization. However, the team's exemplary analysis and reasoning demonstrate how the scientific method can effectively solve mysteries and answer long-standing questions, which in some respects is even colder.
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