Recipe of the terracotta warriors decrypted

Craftsmen used various clay mixtures and manufacturing techniques

The terracotta army impressed by the enormous number and skill of their figures. But their production was surprisingly complex and advanced. © YasmineV / thinkstock
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Surprisingly complex: Researchers have discovered the recipes for which the famous Terracotta Army was produced. The craftsmen therefore used a uniform clay mixture, but depending on the purpose, various ingredients were added. A tight organization and a firm division of labor ensured uniform standards. Contrary to previous assumptions, the clay figurines must also have been fired in solid furnaces, as material analyzes suggest.

Generals, Archers, Infantry, Officers, Charioteers: The Terracotta Army of Chinese Emperor Qin Shihuangdi is unique and world famous. The Emperor had more than 7, 000 life-like figures made for his tomb and put into war formations. A large part of these soldiers was assembled from prefabricated parts and then individually decorated and equipped with amazing lifelike facial expressions. Analyzes also show that the figures were once painted colorful.

How were they made?

However, it has remained mysterious how and where the countless figures were produced. "Because of their size and weight, it is believed that the clay figures were made in or near the mausoleum, but so far, neither workshops nor production waste has been discovered in its surroundings, " Patrick Sean Quinn of University College London and his colleagues say Colleagues.

The technique with which the Tonkrieger were made is as unclear as it is contentious. Some researchers suggest that the craftsmen used mostly unfired clay. But there are also analyzes that point to a burning of the material. In order to gain more insight into the clay warrior's manufacturing process, Quinn and his colleagues have analyzed samples of 14 terracotta figures and compared them to samples of five clay tiles from the soil and remnants of the clay filling of three bronze statues from the grave.

Three different recipes

The analysis revealed that although the raw material for all buildings and figures was the same, it was refined and supplemented in three different ways depending on the purpose. The base was a lime-free clay containing numerous grains of quartz and biotite. This probably came from the extensive loess layers in the immediate vicinity of the tomb, as the researchers report. display

Set up in a battle formation: view over the largest pit of the mausoleum. Richard Chambers / CC-by-sa 3.0

For the bricks of the walls and the soil in the burial chambers, the imperial craftsmen used the clay largely untreated. The clay mixture was only pressed into shape and dried as their microstructure shows. The analysis also suggests that these bricks were not fired.

Special mixtures for the figures

The figures are different, however: for the statue of the dead warriors, the artisans mixed the raw clay with fine river sand, as microscopic photographs revealed. "This sand improved the stickiness of the fine clay, making it easier to sculpt the artful warrior and artist figures, " Quinn and his colleagues explain. "In addition, the sand produced pores in the clay, which allowed the water to evaporate better during drying."

The analyzes also suggest that the clay figures were fired after drying at around 750 degrees about 150 degrees less than previously thought. "That's why there must have been closed, permanent firings, " explain the researchers. "It was only in them that the clay could be heated so slowly that the chemically bound water escaped from the thick walls of the statuary without cracking." At the same time, only these holes ensured a steady and even high temperature,

Why, however, hardly any remains of such bisfen were found until today, remains open. Quinn and his colleagues suspect that most of the workshops were dismantled after the tomb was completed in 210 BC.

The molds for the bronze figures, here a horse team, were made of a special clay mixture. Maros Mraz / CC-by-sa 3.0

Pore ​​builder for the bronze statues

For the bronze figures, the craftsmen mixed the sand-clay mixture with shredded plant material. "This charred and partially burned while burning and left behind characteristic hollows, " the researchers said. The emperor's workers could have used this technique to reduce the weight of the clay filling. At the same time, however, the many air holes made it easier after firing to knock the filling out of the hollow bronze figure.

"Contrary to previous assumptions, a surprisingly complex process was used to obtain a suitable paste for the production of the figures from the raw material, " the scientists report. This suggests that the various clay products were also made by different groups of workers - each was specially trained for the process.

A central "material issue"

The uniform composition of the loam base in all recipes, however, suggests that there was a central "factory" for the preparation of the basic clay at the mausoleum. The individual workshops then received their raw material and processed it further. "This ensured that the standardized basic recipe was used everywhere, " the researchers said.

The division of labor and efficient material flows could explain why the huge mausoleum could be finished in a comparatively short time. A tight organization apparently made sure that each of the approximately 700, 000 workers and craftsmen knew exactly what he had to do and for which sub-process he and his group were responsible. (Antiquity, 2017; doi: 10.15184 / aqy.2017.126)

(Antiquity, 30.08.2017 - NPO)