In 1974, a farmer in Xian, China, stumbled onto one of the most important archaeological finds in history. While digging a well, he uncovered a 2,200-year-old clay sculpture of a soldier.
The worker had discovered the tomb of China’s first emperor, Qin Shihuang, who unified the country in the third century BCE. Archaeologists have since excavated more than 8,000 life-sized soldiers, 130 chariots and 670 horses. Each of them is uniquely and individually created in terracotta, an earthenware clay. Historians estimate that 700,000 laborers spent 30 years working on the memorial.
China has been working for decades to restore the memorial site. One challenge is that these fragile sculptures were immersed in water-soaked soil for more than two millennia, compromising their original appearance. Experts know that the army was originally painted in bright colors, thanks to traces of pigmentation still present. But they didn’t know what materials were used to bind the pigmentation to the terracotta.
A few years ago, a team of European researchers employed a technique normally used in proteomics – matrix-assisted laser desorption/ionization time-of-flight mass spectrometry – to study the sculptures. This technique provides high levels of sensitivity using very small samples. Their equipment included an Agilent gas chromatograph, mass spectrometer and columns.
The researchers determined that the polychrome pigments included cinnabar, apatite, azurite and malachite. Egg and animal glue was used to bind the pigment to the clay. Finally, the finished sculptures were covered with several layers of lacquer from East Asian lacquer trees.
As the researchers wrote, their analysis “represents one of the first steps towards an understanding of the painting technique used on ancient sculptures in China, of which – despite their fame – nothing is yet known.”
Thanks to Agilent Applications Chemist Andy Coffey for suggesting today’s blog topic!
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