Porcelain


Porcelain is a ceramic material made by heating materials, generally including a material like kaolin, in a kiln to temperatures between. The toughness, strength, and translucence of porcelain, relative to other types of pottery, arises mainly from vitrification and the formation of the mineral mullite within the body at these high temperatures. Though definitions vary, porcelain can be divided into three main categories: hard-paste, soft-paste and bone china. The category that an object belongs to depends on the composition of the paste used to make the body of the porcelain object and the firing conditions.
Porcelain slowly evolved in China and was finally achieved at some point about 2,000 to 1,200 years ago, then slowly spread to other East Asian countries, and finally Europe and the rest of the world. Its manufacturing process is more demanding than that for earthenware and stoneware, the two other main types of pottery, and it has usually been regarded as the most prestigious type of pottery for its delicacy, strength, and its white colour. It combines well with both glazes and paint, and can be modelled very well, allowing a huge range of decorative treatments in tablewares, vessels and figurines. It also has many uses in technology and industry.
The European name, porcelain in English, comes from the old Italian porcellana because of its resemblance to the surface of the shell. Porcelain is also referred to as china or fine china in some English-speaking countries, as it was first seen in imports from China. Properties associated with porcelain include low permeability and elasticity; considerable strength, hardness, toughness, whiteness, translucency and resonance; and a high resistance to chemical attack and thermal shock.
swan tureen, 1752–1756, Chelsea porcelain
Porcelain has been described as being "completely vitrified, hard, impermeable, white or artificially coloured, translucent, and resonant". However, the term "porcelain" lacks a universal definition and has "been applied in an unsystematic fashion to substances of diverse kinds which have only certain surface-qualities in common".
Traditionally, East Asia only classifies pottery into low-fired wares and high-fired wares, the latter also including what Europeans call stoneware, which is high-fired but not generally white or translucent. Terms such as "proto-porcelain", "porcellaneous" or "near-porcelain" may be used in cases where the ceramic body approaches whiteness and translucency.

Types

Hard paste

Hard-paste porcelain was invented in China, and also used in Japanese porcelain, and most of the finest quality porcelain wares are in this material. The earliest European porcelains were produced at the Meissen factory in the early 18th century; they were formed from a paste composed of kaolin and alabaster and fired at temperatures up to in a wood-fired kiln, producing a porcelain of great hardness, translucency, and strength. Later, the composition of the Meissen hard paste was changed and the alabaster was replaced by feldspar and quartz, allowing the pieces to be fired at lower temperatures. Kaolinite, feldspar and quartz continue to constitute the basic ingredients for most continental European hard-paste porcelains.

Soft paste

Soft-paste porcelains date back from the early attempts by European potters to replicate Chinese porcelain by using mixtures of clay and frit. Soapstone and lime were known to have been included in these compositions. These wares were not yet actual porcelain wares as they were not hard nor vitrified by firing kaolin clay at high temperatures. As these early formulations suffered from high pyroplastic deformation, or slumping in the kiln at high temperatures, they were uneconomic to produce and of low quality.
Formulations were later developed based on kaolin with quartz, feldspars, nepheline syenite or other feldspathic rocks. These were technically superior, and continue to be produced. Soft-paste porcelains are fired at lower temperatures than hard-paste porcelain, therefore these wares are generally less hard than hard-paste porcelains.

Bone china

Although originally developed in England in 1748 to compete with imported porcelain, bone china is now made worldwide, including China. The English had read the letters of Jesuit missionary François Xavier d'Entrecolles, which described Chinese porcelain manufacturing secrets in detail. One writer has speculated that a misunderstanding of the text could possibly have been responsible for the first attempts to use bone-ash as an ingredient of English porcelain, although this is not supported by researchers and historians.
Traditionally, English bone china was made from two parts of bone ash, one part of kaolin and one part china stone, although this has largely been replaced by feldspars from non-UK sources. But for example Royal Crown Derby still uses 50% bone ash in the 21st century.

Materials

is the primary material from which porcelain is made, even though clay minerals might account for only a small proportion of the whole. The word paste is an old term for both the unfired and fired materials. A more common terminology for the unfired material is "body"; for example, when buying materials a potter might order an amount of porcelain body from a vendor.
The composition of porcelain is highly variable, but the clay mineral kaolinite is often a raw material. Other raw materials can include feldspar, ball clay, glass, bone ash, steatite, quartz, petuntse and alabaster.
The clays used are often described as being long or short, depending on their plasticity. Long clays are cohesive and have high plasticity; short clays are less cohesive and have lower plasticity. In soil mechanics, plasticity is determined by measuring the increase in content of water required to change a clay from a solid state bordering on the plastic, to a plastic state bordering on the liquid, though the term is also used less formally to describe the ease with which a clay may be worked.
Clays used for porcelain are generally of lower plasticity and are shorter than many other pottery clays. They wet very quickly, meaning that small changes in the content of water can produce large changes in workability. Thus, the range of water content within which these clays can be worked is very narrow and consequently must be carefully controlled.

Production

Forming

Porcelain can be made using all the shaping techniques for pottery. It was originally typically made on the potter's wheel, though moulds were also used from early on. Slipcasting has been the most common commercial method in recent times.

Glazing

is unglazed porcelain treated as a finished product, mostly for figures and sculpture. Unlike their lower-fired counterparts, porcelain wares do not need glazing to render them impermeable to liquids and for the most part are glazed for decorative purposes and to make them resistant to dirt and staining. Many types of glaze, such as the iron-containing glaze used on the celadon wares of Longquan, were designed specifically for their striking effects on porcelain.

Decoration

Porcelain often receives underglaze decoration using pigments that include cobalt oxide and copper, or overglaze enamels, allowing a wider range of colours. Like many earlier wares, modern porcelains are often biscuit-fired at around, coated with glaze and then sent for a second glaze-firing at a temperature of about or greater. Another early method is "once-fired", where the glaze is applied to the unfired body and the two fired together in a single operation.

Firing

In this process, "green" ceramic wares are heated to high temperatures in a kiln to permanently set their shapes, vitrify the body and the glaze. Porcelain is fired at a higher temperature than earthenware so that the body can vitrify and become non-porous. Many types of porcelain in the past have been fired twice or even three times, to allow decoration using less robust pigments in overglaze enamel.

History

Chinese porcelain

Porcelain was invented in China over a centuries-long development period beginning with "proto-porcelain" wares dating from the Shang dynasty. By the time of the Eastern Han dynasty these early glazed ceramic wares had developed into porcelain, which Chinese defined as high-fired ware. By the late Sui dynasty and early Tang dynasty, the now-standard requirements of whiteness and translucency had been achieved, in types such as Ding ware. The wares were already exported to the Islamic world, where they were highly prized.
Eventually, porcelain and the expertise required to create it began to spread into other areas of East Asia. During the Song dynasty, artistry and production had reached new heights. The manufacture of porcelain became highly organised, and the dragon kilns excavated from this period could fire as many as 25,000 pieces at a time, and over 100,000 by the end of the period. While Xing ware is regarded as among the greatest of the Tang dynasty porcelain, Ding ware became the premier porcelain of the Song dynasty. By the Ming dynasty, production of the finest wares for the court was concentrated in a single city, and Jingdezhen porcelain, originally owned by the imperial government, remains the centre of Chinese porcelain production.
By the time of the Ming dynasty, porcelain wares were being exported to Asia and Europe. Some of the most well-known Chinese porcelain art styles arrived in Europe during this era, such as the coveted "blue-and-white" wares. The Ming dynasty controlled much of the porcelain trade, which was expanded to Asia, Africa and Europe via the Silk Road. In 1517, Portuguese merchants began direct trade by sea with the Ming dynasty, and in 1598, Dutch merchants followed.
Some porcelains were more highly valued than others in imperial China. The most valued types can be identified by their association with the court, either as tribute offerings, or as products of kilns under imperial supervision. Since the Yuan dynasty, the largest and best centre of production has made Jingdezhen porcelain. During the Ming dynasty, Jingdezhen porcelain become a source of imperial pride. The Yongle emperor erected a white porcelain brick-faced pagoda at Nanjing, and an exceptionally smoothly glazed type of white porcelain is peculiar to his reign. Jingdezhen porcelain's fame came to a peak during the Qing dynasty.

Japanese porcelain

Although the Japanese elite were keen importers of Chinese porcelain from early on, they were not able to make their own until the arrival of Korean potters that were taken captive during the Japanese invasions of Korea. They brought an improved type of kiln, and one of them spotted a source of porcelain clay near Arita, and before long several kilns had started in the region. At first their wares were similar to the cheaper and cruder Chinese porcelains with underglaze blue decoration that were already widely sold in Japan; this style was to continue for cheaper everyday wares until the 20th century.
Exports to Europe began around 1660, through the Chinese and the Dutch East India Company, the only Europeans allowed a trading presence. Chinese exports had been seriously disrupted by civil wars as the Ming dynasty fell apart, and the Japanese exports increased rapidly to fill the gap. At first the wares used European shapes and mostly Chinese decoration, as the Chinese had done, but gradually original Japanese styles developed.
Nabeshima ware was produced in kilns owned by the families of feudal lords, and were decorated in the Japanese tradition, much of it related to textile design. This was not initially exported, but used for gifts to other aristocratic families. Imari ware and Kakiemon are broad terms for styles of export porcelain with overglaze "enamelled" decoration begun in the early period, both with many sub-types.
A great range of styles and manufacturing centres were in use by the start of the 19th century, and as Japan opened to trade in the second half, exports expanded hugely and quality generally declined. Much traditional porcelain continues to replicate older methods of production and styles, and there are several modern industrial manufacturers. By the early 1900's, Filipino porcelain artisans working in Japanese porcelain centres for much of their lives, later on introduced the craft into the native population in the Philippines.

European porcelain

These exported Chinese porcelains were held in such great esteem in Europe that in English became a commonly–used synonym for the Italian term porcelain. The first mention of porcelain in Europe is in Il Milione by Marco Polo in the 13th century. Apart from copying Chinese porcelain in faience, the soft-paste Medici porcelain in 16th-century Florence was the first real European attempt to reproduce it, with little success.
Early in the 16th century, Portuguese traders returned home with samples of kaolin, which they discovered in China to be essential in the production of porcelain wares. However, the Chinese techniques and composition used to manufacture porcelain were not yet fully understood. Countless experiments to produce porcelain had unpredictable results and met with failure. In the German state of Saxony, the search concluded in 1708 when Ehrenfried Walther von Tschirnhaus produced a hard, white, translucent type of porcelain specimen with a combination of ingredients, including kaolin and alabaster, mined from a Saxon mine in Colditz. It was a closely guarded trade secret of the Saxon enterprise.
In 1712, many of the elaborate Chinese porcelain manufacturing secrets were revealed throughout Europe by the French Jesuit father Francois Xavier d'Entrecolles and soon published in the Lettres édifiantes et curieuses de Chine par des missionnaires jésuites. The secrets, which d'Entrecolles read about and witnessed in China, were now known and began seeing use in Europe.

Meissen

Von Tschirnhaus and Johann Friedrich Böttger were employed by Augustus II the Strong and worked at Dresden and Meissen in the German state of Saxony. Tschirnhaus had a wide knowledge of science and had been involved in the European quest to perfect porcelain manufacture when, in 1705, Böttger was appointed to assist him in this task. Böttger had originally been trained as a pharmacist; after he turned to alchemical research, he claimed to have known the secret of transmuting dross into gold, which attracted the attention of Augustus. Imprisoned by Augustus as an incentive to hasten his research, Böttger was obliged to work with other alchemists in the futile search for transmutation and was eventually assigned to assist Tschirnhaus. One of the first results of the collaboration between the two was the development of a red stoneware that resembled that of Yixing.
A workshop note records that the first specimen of hard, white and European porcelain was produced in 1708. At the time, the research was still being supervised by Tschirnhaus; however, he died in October of that year. It was left to Böttger to report to Augustus in March 1709 that he could make porcelain. For this reason, credit for the European discovery of porcelain is traditionally ascribed to him rather than Tschirnhaus.
The Meissen factory was established in 1710 after the development of a kiln and a glaze suitable for use with Böttger's porcelain, which required firing at temperatures of up to to achieve translucence. Meissen porcelain was once-fired, or green-fired. It was noted for its great resistance to thermal shock; a visitor to the factory in Böttger's time reported having seen a white-hot teapot being removed from the kiln and dropped into cold water without damage. Although widely disbelieved this has been replicated in modern times.

Soft paste porcelain

The pastes produced by combining clay and powdered glass were called Frittenporzellan in Germany and frita in Spain. In France they were known as pâte tendre and in England as "soft-paste". They appear to have been given this name because they do not easily retain their shape in the wet state, or because they tend to slump in the kiln under high temperature, or because the body and the glaze can be easily scratched.
;France
Experiments at Rouen produced the earliest soft-paste in France, but the first important French soft-paste porcelain was made at the Saint-Cloud factory before 1702. Soft-paste factories were established with the Chantilly manufactory in 1730 and at Mennecy in 1750. The Vincennes porcelain factory was established in 1740, moving to larger premises at Sèvres in 1756. Vincennes soft-paste was whiter and freer of imperfections than any of its French rivals, which put Vincennes/Sèvres porcelain in the leading position in France and throughout the whole of Europe in the second half of the 18th century.
;Italy
Doccia porcelain of Florence was founded in 1735 and remains in production, unlike Capodimonte porcelain which was moved from Naples to Madrid by its royal owner, after producing from 1743 to 1759. After a gap of 15 years Naples porcelain was produced from 1771 to 1806, specializing in Neoclassical styles. All these were very successful, with large outputs of high-quality wares. In and around Venice, Francesco Vezzi was producing hard-paste from around 1720 to 1735; survivals of Vezzi porcelain are very rare, but less so than from the Hewelke factory, which only lasted from 1758 to 1763. The soft-paste Cozzi factory fared better, lasting from 1764 to 1812. The Le Nove factory produced from about 1752 to 1773, then was revived from 1781 to 1802.
; England
The first soft-paste in England was demonstrated by Thomas Briand to the Royal Society in 1742 and is believed to have been based on the Saint-Cloud formula. In 1749, Thomas Frye took out a patent on a porcelain containing bone ash. This was the first bone china, subsequently perfected by Josiah Spode.
In the twenty-five years after Briand's demonstration, a number of factories were founded in England to make soft-paste tableware and figures:
discovered deposits of kaolin in Cornwall, making a considerable contribution to the development of porcelain and other whiteware ceramics in the United Kingdom. Cookworthy's factory at Plymouth, established in 1768, used kaolin and china stone to make porcelain with a body composition similar to that of the Chinese porcelains of the early 18th century.

Other uses

Electric insulating material

Porcelain and other ceramic materials have many applications in engineering, especially ceramic engineering. Porcelain is an excellent insulator for use with high voltages, especially in outdoor applications. Examples include: terminals for high-voltage cables, bushings of power transformers, and insulation of high-frequency antennas.

Building material

Porcelain can be used as a building material, usually in the form of tiles or large rectangular panels. Modern porcelain tiles are generally produced by a number of recognised international standards and definitions. Manufacturers are found across the world with Italy being the global leader, producing over 380 million square metres in 2006. Historic examples of rooms decorated entirely in porcelain tiles can be found in several European palaces including ones at Galleria Sabauda in Turin, Museo di Doccia in Sesto Fiorentino, Museo di Capodimonte in Naples, the Royal Palace of Madrid and the nearby Royal Palace of Aranjuez. and the Porcelain Tower of Nanjing.
More recent noteworthy examples include the Dakin Building in Brisbane, California, and the Gulf Building in Houston, Texas, which when constructed in 1929 had a porcelain logo on its exterior. A more detailed description of the history, manufacture and properties of porcelain tiles is given in the article “Porcelain Tile: The Revolution Is Only Beginning.”

Bathroom fittings

Because of its durability, inability to rust and impermeability, glazed porcelain has been in use for personal hygiene since at least the third quarter of the 17th century. During this period, porcelain chamber pots were commonly found in higher-class European households, and the term "bourdaloue" was used as the name for the pot.
However bath tubs are not made of porcelain, but of porcelain enamel on a metal base, usually of cast iron. Porcelain enamel is a marketing term used in the US, and is not porcelain but vitreous enamel.

Dental porcelain

is used for crowns, bridges and veneers.

Manufacturers