Scientists solve the mystery of the pristine weapons of China's terracotta warriors

(Reuters) – For decades, scientists have been puzzled by the wonderful conservation of the bronze weapons associated with the famous Terracotta Warriors, retaining almost intact glossy surfaces and sharp blades after being buried for more than two millennia.

Research conducted Thursday by an international team of scientists could solve the mystery while concealing an intriguing assumption: ancient Chinese artisans used an unexpected method of conservation, using metallic chromium.

The good conservation of weapons, including swords, spears and halberds, was due to chance reasons – factors such as the bronze's high bronze content and favorable soil composition, scientists decided after examining 464 weapons and bronze coins.

They determined that the chromium on the bronze surfaces was simply a contamination by a lacquer rich in chrome applied by the artisans to the terracotta figurines and the pieces of arms. Chromium has no role in their preservation.

The Terracotta Army is made up of thousands of ceramic warriors and horses, bronze tanks and weapons, and is part of the vast mausoleum of the 3rd century BC. AD located near the city of Xi'an for Qin Shi Huang, first emperor of a unified China. Founded in 1974, it represents one of the greatest archaeological discoveries of the twentieth century.

Nearly forty years of scientific analysis detected the presence of chromium on the surface of certain weapons, which led to the hypothesis that the arms manufacturers applied a treatment to chrome base to prevent corrosion.

The chrome conversion coating technology, discovered in the early 20th century, is used to treat metals to make them more resistant to corrosion. It involves soaking metal in a solution containing chromium salts. A layer of chromium oxide is deposited on the surface of the metal, providing a barrier against rust.

"The lacquer was applied to the Terracotta Army as a primer before being painted with colors. We think it's probably applied equally to wooden pieces, such as handles and drums, that have broken down, "said Marcos, a scientist in archeology at the University of Cambridge. Martinón-Torres, who led the study published in the journal Scientific Reports.

Ancient bronzes often have mediocre states of preservation, with porous, pricked surfaces with green or dark colors.

"In essence, we show that, yes, the weapons of the Terracotta Army generally show a very good state of preservation, but nothing indicates for the moment that this is anything other than the result of". a chance, "added Martinón-Torres, who has been involved in research at University College London and in collaboration with the Terracotta Army Museum.