China’s Terracotta Army has fascinated millions since its discovery 40 years ago, near present-day Xi’an. Built by Qin Shihuang, China’s first emperor, the Terracotta Army was massed below ground, to protect a spectacular underground palace complex that was based on Qin’s imperial capital.
To create his Terracotta Army, Qin “issued instructions that his imperial guard be replicated, down to the finest details, in red-brown terracotta clay, poised to do battle,” according to Science China Press.
When the army was uncovered in 1974, thousands of these imperial guards were initially discovered, with some containing patches of pigment that had survived 22 centuries buried underground, along with minute remnants of binding media that had aided in the creation of this polychrome Terracotta Army, the publication added.
Since then, efforts to conserve these figures from China’s First Empire have been hindered by scientists’ inability to discover the binding material used in applying pigments to Qin Shihuang’s underground army.
However, recent research has revealed “the surfaces of the terracotta warriors were initially covered with one or two layers of an East Asian lacquer … obtained from lacquer trees,” according to Hongtao Yan and Jingjing An, scientists at the College of Chemistry and Materials Science, Northwest University, in Xi’an.
“This lacquer was used as a base-coat for the polychrome layers, with one layer of polychrome being placed on top of the lacquer in the majority of cases,” according to an article co-authored by Tie Zhou, Yin Xia and Bo Rong, scholars at the Key Scientific Research Base of Ancient Polychrome Pottery Conservation, the State Administration for Cultural Heritage, which is connected with the Museum of Emperor Qin Shihuang‘s Terracotta Army.
Qin (260-210 BC) united China in 221 BC and ruled as the First Emperor of the Qin dynasty from 220 to 210 BC. The approximately 8,000 terracotta warriors found in Qin’s underground palace were to protect the emperor in the afterlife.
The United Nations Educational, Scientific and Cultural Organization described the site in glowing terms more than a quarter century ago: “Qin … is buried, surrounded by the famous terracotta warriors, at the center of a complex designed to mirror the urban plan of the capital, Xianyang. The small figures are all different; with their horses, chariots and weapons, they are masterpieces of realism and also of great historical interest.”
UNESCO described the site as one of the most fabulous archaeological reserves in the world. “The documentary value of a group of hyper realistic sculptures where no detail has been neglected – from the uniforms of the warriors, their arms, to even the horses’ halters – is enormous. Furthermore, the information to be gleaned from the statutes concerning the craft and techniques of potters and bronze-workers is immeasurable.”
The study, published in the Chinese Science Bulletin, states that polychrome layers applied to these sculpted imperial guards were composed of natural inorganic pigments and binding media. These pigments have been identified as including cinnabar, apatite, azurite and malachite, but the precise composition of binding media, which relied on proteins, used in the painting process had long eluded scientists.
“Research aimed at solving this puzzle faced an array of obstacles: extremely low levels the proteinaceous binding media in the polychrome layers of Qin Shihuang’s terracotta army have survived being submerged in almost six meters of water-saturated loess for more than two millennia,” according to Science China Press.
“Following almost 22 centuries of storage under these conditions, the remaining pieces of original polychromy that have survived on the sculptures contain extremely small amounts of the binding media,” the researchers wrote.
A substantial amount of the polychromy has already been lost through pillaging as well as damage from fire and water, they explained.
To solve the more than 2000-year-old enigma, these researchers used matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to identify the binding material. This offers high levels of sensitivity, requires only a minimal sample pretreatment process and can be used to reliably identify different types of proteinaceous material, according to Science China Press.
The researchers prepared “artificially aged” model samples by mixing different pigments with either animal glue or an adhesive concocted from free-range chicken eggs. To replicate the processes involved in the degradation of the pigments and binding media of the actual terracotta warriors, the model samples were buried in loess soil at a depth of one meter for one year.
Historical samples of the polychrome terracotta army were obtained from the Museum of Emperor Qin Shihuang’s Terracotta Army in Xi’an to facilitate a comparative analysis.
(HT: A Blog About History)