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The stone which made possible the 8th Wonder of the world

каолинит
© Форпост Северо-Запад / Горный музей

Kaolinite was first discovered in the Chinese province of Gaolin, near the town of Jingdezhen, several centuries before Christ. The stone was part of the white clay that was given the same name as kaolin. Chinese craftsmen mastered the technique of working this material, and in the 2nd century B.C. one of the main attractions of the Celestial Empire, included in the UNESCO World Heritage List, the Terracotta Army, was created from it.

This is more than eight thousand ceramic figures of soldiers, horses and chariots, made in real scale. They were buried underground in a tomb with the first emperor of the Qin Dynasty, Shi Huangdi, who unified China and joined all the links of the Great Wall. A year after ascending the throne, as a thirteen-year-old teenager, the emperor began construction of his future tomb, which lasted almost forty years. According to ancient Chinese tradition, the ruler had to bury with himself 4,000 young soldiers, who would protect him in the afterlife. Shi Huangdi, however, understood that such mass executions would definitely cause people to ask uncomfortable questions; and decided to take with him the clay statues of the soldiers. The number of statues was doubled for extra protection.

каолинит
© Форпост Северо-Запад / Горный музей

All the sculptures were executed with jewel-like precision: not a single expression or hairstyle couldn’t be found among the faces, and the details of clothing and ammunition were created with incredible fidelity. Scientists speculate that the body with a monolithic and solid lower part and a hollow upper part was first molded from kaolin. The body was then kiln-fired for several days at about 800 degrees Celsius, after which the arms and legs were attached and an additional layer of clay was applied to the face to personalize it. Artists painted the resulting figures in their natural colors. The clay soldiers were destined to remain in the ground for more than 2,000 years since the death of Shi Huangdi, before they were accidentally discovered in 1974 by a Chinese peasant who decided to dig a well on his property. It’s only natural to imagine the level of awe in the expression of the peasant.

каолинит
© Форпост Северо-Запад / Горный музей

Another use for kaolinite was found by Chinese artisans in the manufacture of porcelain. Constant experimentation with clay and techniques of its processing led to a flowering of porcelain industry in China. Workshops existed in almost every town, and the "porcelain capital" of the world was Tszindechen. The entire population here worked exclusively in the production of ceramics. It was possible to enter the city only with a password, and at night its streets were guarded by armed patrols. That’s how Chinese authorities took care to keep the recipe for porcelain a secret. For a long time, in other countries, this kind of pottery was literally worth its weight in gold: a cup was paid for as much precious metal as it weighed. Even broken pieces were kept and passed down. Ornaments made of shards of porcelain were the fashionable trend of the 18th century. The recipe for pottery remained an unsolved mystery to Europeans for four centuries.

каолинит
© Форпост Северо-Запад / Горный музей

There were many nuances in the making of classic Chinese porcelain. The molding mass consisted of kaolin clay mined only in a few areas of the country and the finest mineral powder. But to make it malleable, the mixture was aged for 10 years before use. The firing temperature was 1,300 degrees Celsius and kept in the kiln for four days.

Kaolinite was valued not only as a material to create products, but also as an antiseptic. The useful properties of white clay were first described by Hippocrates. The ancient Greek scientist found that kaolin was able to stop inflammatory processes in tissues and disinfect wounds. In everyday life, it was used to store food: food was stored in clay containers, previously wrapped in cloth moistened with cold water. With this system the food did not spoil for a long time and retained its properties. Today, masks based on white clay, which has antimicrobial action, are recommended by cosmetologists for cleansing the skin of dead cells, whitening, improving blood circulation, strengthening capillaries, smoothing wrinkles and fighting acne.

каолинит
© Форпост Северо-Запад / Горный музей

The main consumer of this mineral remains the porcelain and ceramic industry, just as it was two thousand years ago. In such an industry as mining, kaolinite, being a component of kaolin clays; is used for drilling in difficult mining and geological conditions. Scientists at St. Petersburg Mining University are conducting research into the use of kaolin clays to strengthen wells under abnormally low reservoir pressures.

"When drilling for oil and gas, one of the main and most difficult tasks is to provide high-quality interlayer isolation in the annulus. The efficiency of well operation, tightness, "life" length and the cost of the produced material depend on the quality of wellbore isolation. This is indeed a current problem for the majority of Western and Eastern Siberia fields, which are characterized by permafrost rocks and low-pressure formations. When cementing with plugging solution in such conditions, it is often absorbed and the formation is contaminated, as a result the ability to contain and pass fluids is reduced. Scientific experiments conducted by Mining University scientists prove that kaolin clays have serious potential for use as a facilitating additive to plugging solutions. This material, which has a lower density, makes it possible to improve the quality of well cementing by creating a strong and impermeable layer and thus improve the quality of interbedded formation isolation," explained Maria Nutskova, assistant professor of the Well Drilling Department at the St. Petersburg Mining University.

буровая
© gazprom-neft.ru

Translated by Diego Monterrey, for Northwest Forpost.