Porcelain

• 1. Introduction

  ›

  Porcelain takes its English name from an old Italian word, porcellana, meaning cowrie shell. Early Europeans thought its smooth surface resembled the shell, so the name stuck. To make it, raw materials including kaolinite are heated in a kiln to temperatures between 1200 and 1400 degrees Celsius. At that heat, the body vitrifies and a mineral called mullite forms inside it. Those two changes give porcelain its strength and its faint translucence. For centuries it has been regarded as the most prestigious type of pottery. The reasons given are its delicacy, its strength, and its high degree of whiteness. Yet the word itself resists definition. It has been applied in an unsystematic fashion to substances of diverse kinds that share only certain surface qualities. So what exactly counts as porcelain, and what does not? Who first managed to make it, and who spent generations trying to copy them? And how did a material first valued for teacups end up holding back electricity on power lines and forming the crowns inside human mouths?

• 2. The Three Pastes

  ›

  Hard-paste porcelain was invented in China and later used in Japanese porcelain too. Most of the finest quality wares are made from this material. The earliest European versions came from the Meissen factory in the early 18th century. They used a paste of kaolin and alabaster, fired in a wood-fired kiln at up to 1400 degrees Celsius. Later the alabaster was swapped for feldspar and quartz, which allowed firing at lower temperatures. Kaolinite, feldspar, and quartz remain the basic ingredients for most continental European hard-paste porcelains.

  Soft-paste porcelains began as European attempts to replicate Chinese porcelain using mixtures of clay and frit. Soapstone and lime were included in some of these early compositions. They were not true porcelain, since they were neither hard nor vitrified by firing kaolin clay at high heat. These first formulations slumped in the kiln at high temperatures, which made them uneconomic and low in quality. Later versions based on kaolin with quartz, feldspars, or nepheline syenite proved technically superior and are still produced.

  Bone china was developed in England in 1748 to compete with imported porcelain, and is now made worldwide, including in China. Traditional English bone china used two parts bone ash, one part kaolin, and one part china stone. The china stone has since been replaced by feldspars from sources outside the United Kingdom. The categories differ in the composition of the body and in the firing conditions. One writer speculated that a misreading of a Jesuit account of Chinese methods led to the first use of bone ash in English porcelain.

• 3. Clay That Wets Too Fast

  ›

  Kaolin is the primary material from which porcelain is made, even though clay minerals may account for only a small proportion of the whole. Potters call the unfired material the body, while paste is an older term for both fired and unfired states. Beyond kaolinite, raw materials can include feldspar, ball clay, glass, bone ash, steatite, quartz, petuntse, and alabaster.

  Clays used for porcelain are generally of lower plasticity than many other pottery clays. They are often described as long or short depending on how cohesive and workable they are. Long clays are sticky and highly plastic, while short clays are less cohesive. Porcelain clays wet very quickly, so small changes in water content produce large changes in workability. The window in which they can be worked is narrow, which is why the water content must be carefully controlled.

• 4. Glaze And Fire

  ›

  Biscuit porcelain is unglazed porcelain treated as a finished product, used mostly for figures and sculpture. Unlike lower-fired pottery, porcelain does not need glaze to keep liquids out, since the body itself becomes impermeable. Glaze is applied mainly for decoration and to resist dirt and staining. Some glazes were designed for their effect on porcelain, such as the iron-containing glaze on the celadon wares of Longquan.

  Underglaze decoration often uses pigments such as cobalt oxide and copper, while overglaze enamels allow a wider range of colours. Modern porcelains are frequently biscuit-fired at around 1000 degrees Celsius, then glazed and fired again at about 1300 degrees Celsius or greater. An early alternative is the once-fired method, where glaze is applied to the unfired body and the two are fired together. During firing, green wares are heated until their shapes are permanently set and the body vitrifies into a non-porous state. Some porcelains in the past were fired twice or even three times to allow decoration with less robust overglaze pigments.

• 5. China's Long Invention

  ›

  Proto-porcelain wares date from the Shang dynasty, which ran from 1600 to 1046 BCE. By the Eastern Han dynasty, from 25 to 220 CE, these glazed wares had developed into what the Chinese defined as high-fired ware. The standard requirements of whiteness and translucency were achieved by the late Sui and early Tang dynasties, in types such as Ding ware. These wares were already exported to the Islamic world, where they were highly prized.

  During the Song dynasty, from 960 to 1279 CE, production reached new heights of organisation. Dragon kilns from this period could fire as many as 25,000 pieces at a time, and over 100,000 by the end of the era. Xing ware ranks among the greatest of the Tang dynasty, while Ding ware became the premier porcelain of the Song. Since the Yuan dynasty, the largest and best centre of production has made Jingdezhen porcelain.

  By the Ming dynasty, from 1368 to 1644 CE, porcelain was exported to Asia, Africa, and Europe along the Silk Road. The coveted blue-and-white wares reached Europe in this era. In 1517, Portuguese merchants began direct sea trade with the Ming dynasty, and Dutch merchants followed in 1598. The Yongle emperor erected a white porcelain brick-faced pagoda at Nanjing, and a smoothly glazed white porcelain peculiar to his reign survives from his court.

• 6. Japan And Korea

  ›

  Korean potters taken captive during the Japanese invasions of Korea, from 1592 to 1598, gave Japan its first porcelain. They brought an improved kiln, and one of them found a source of porcelain clay near Arita. Before long several kilns had started in the region. Their first wares resembled cheap Chinese porcelain with underglaze blue decoration, a style that continued for everyday wares into the 20th century. Exports to Europe began around 1660 through the Chinese and the Dutch East India Company, the only Europeans allowed to trade there.

  Nabeshima ware was produced in kilns owned by the families of feudal lords and decorated in the Japanese tradition, much of it related to textile design. It was not exported at first, but given as gifts to other aristocratic families. Imari ware and Kakiemon are broad terms for export styles with overglaze enamelled decoration. By the early 1900s, Filipino artisans who had worked in Japanese centres introduced the craft into the Philippines.

  Olive green glaze appeared in Korea during the late Silla dynasty, and most Silla ceramics are leaf-shaped. In the late 13th century, potters filled the hollow parts of pottery with white and red clay to make pigmented inlay patterns. The key difference from Chinese work is that many Korean specimens carry inlay decoration under the glaze. Most Korean ceramics from the Joseon dynasty show excellent decorative quality, often in an asymmetrical melon shape.

• 7. Europe's Secret War

  ›

  Marco Polo gave the first European mention of porcelain in Il Milione in the 13th century. The soft-paste Medici porcelain made in 16th-century Florence was the first real European attempt to reproduce it, with little success. Early in the 16th century, Portuguese traders brought home samples of kaolin, which they had found essential to Chinese porcelain. Still, the Chinese composition and techniques were not understood, and countless experiments failed unpredictably.

  In Saxony, the search ended in 1708 when Ehrenfried Walther von Tschirnhaus produced a hard, white, translucent specimen. His mixture included kaolin and alabaster mined from a Saxon mine in Colditz, and the result was a closely guarded trade secret. In 1712, the French Jesuit father Francois Xavier d'Entrecolles revealed many Chinese manufacturing secrets across Europe. They were published in the Lettres edifiantes et curieuses de Chine par des missionnaires jesuites.

  Von Tschirnhaus worked with Johann Friedrich Bottger under Augustus II, King of Poland and Elector of Saxony, in Dresden and the town of Meissen. Bottger had trained as a pharmacist before turning to alchemy and claiming he could turn dross into gold. Augustus imprisoned him as an incentive to hasten his research. A workshop note records the first specimen of hard, white, vitrified European porcelain in 1708. Tschirnhaus died in October of that year, so Bottger reported to Augustus in March 1709 that he could make porcelain. For that reason, credit for the European discovery is traditionally given to Bottger. The Meissen factory was established in 1710. A visitor in Bottger's time reported seeing a white-hot teapot pulled from the kiln and dropped into cold water without damage.

• 8. Beyond The Teacup

  ›

  Porcelain has insulated electrical lines since at least 1878, with one source noting earlier use on the telegraph line between Frankfurt and Berlin. Its electrical, mechanical, and thermal properties stay stable even in harsh environments. In 2018, a porcelain bushing insulator made by NGK in Handa, Aichi Prefecture, Japan, was certified as the world's largest ceramic structure by Guinness World Records. It stands 11.3 metres tall and 1.5 metres in diameter. The global high-voltage insulator market was worth 4.95 billion US dollars in 2015, with porcelain holding just over 48 percent.

  Chemical porcelain serves laboratory work, with low thermal expansion, high mechanical strength, and high chemical resistance. It is used for reaction vessels, combustion boats, evaporating dishes, and Buchner funnels, with properties set by standards such as ASTM C515. Porcelain tiles are dense, fine-grained, and usually impervious, and Italy leads the world, producing over 380 million square metres in 2006. The Gulf Building in Houston, Texas, carried a 21 metre porcelain logo when it was built in 1929.

  Glazed porcelain has served personal hygiene since at least the third quarter of the 17th century, when porcelain chamber pots known as bourdaloues appeared in higher-class European households. Modern toilets and washbasins now use vitreous china rather than porcelain. Dental porcelain forms crowns, bridges, and veneers, in a formulation that is 70 to 85 percent feldspar. From a material that once held tea for emperors, porcelain now sits inside human mouths, where roughly one percent colourants tint each crown to match a tooth.