A hard, vitreous, translucent, resonant material, contrasting with opaque, more porous pottery. It contains china clay (kaolin) and chinastone (petuntse), and is fired at a temperature of c.12001350°C, whereas pottery does not contain chinastone, and is fired at a lower temperature. Porcelain was first manufactured by the Chinese in the Tang dynasty (7th10th-c), when production of the famous jade-green celadon ware began. At least nine major variants were produced under the Song (10th13th-c). It found its way to W Europe from c.1300, and was prized as a semi-precious material, often mounted in gold or silver. The first European attempts to make it were at the Medici factory in Florence in the 1570s, but real success was only achieved at Meissen in the early 18th-c.
According to the Combined Nomenclature of the European Communities, porcelain is "completely vitrified, hard, impermeable (even before glazing), white or artificially coloured, translucent (except when of considerable thickness) and resonant." Raw materials for porcelain, when mixed with water, form a plastic paste that can be worked to a required shape before firing in a kiln at temperatures between about 1200 and 1400 degrees Celsius. The toughness, strength, and translucence of porcelain arise mainly from the formation at high temperatures of glass and the mineral mullite.Porcelain was named after its resemblance to the white, shiny Venus-shell, called in old Italian porcella. (Latin porcella, a little pig, a pig)
Properties associated with porcelain include low permeability, high strength, hardness, glassiness, durability, whiteness, translucence, resonance, brittleness, high resistance to the passage of electricity, chemical attack, and thermal shock, and high elasticity.
Porcelain is used to make table, kitchen, sanitary, and decorative wares, objects of fine art, and tile.
Scope, materials and methods
Scope
Porcelain has many uses but this article is concerned mainly with its employment as a material used to make objects of craft and fine art, including decorative and utilitarian household wares.
Materials
The material used to form the body of porcelain wares is often referred to as clay, even though clay minerals might account for only a small proportion of its whole. The porcelain clay body, unfired or fired, is sometimes spoken of as the paste and porcelain clay is itself sometimes described as the body (for example, when buying materials a potter might order such an amount of porcelain body from a vendor).
The composition of porcelain is highly variable, but china clay, comprising mainly or in part the platey clay mineral kaolinite is often a significant component. Other materials mixed with china clay to make porcelain clay have included feldspar, ball-clay, glass, bone ash, steatite, quartz, petuntse and alabaster. Porcelain clays are of lower plasticity (shorter) than many other clays used for making pottery and wet very quickly, which is to say that small changes in the content of water can produce large changes in workability. Thus, the range of water contents within which porcelain clays can be worked is very narrow and the loss or gain of water during storage and throwing or forming must be carefully controlled to keep the clay from becoming too wet or too dry to manipulate
Methods
The Wikipedia article on Pottery provides much useful background information on methods used for forming, decorating, finishing, glazing and firing ceramic wares.
Forming. Porcelain wares can be formed by any of the shaping methods listed in the Pottery article.
The relatively low plasticity of the clays used for making porcelain can cause difficulties for the potter, particularly in the case of wheel-thrown wares. 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. Great detail is given in the glaze article.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 wares may be decorated under the glaze, using pigments that include cobalt and copper, or over the glaze using coloured enamels. In common with many earlier wares, modern porcelain wares are often bisque-fired at around 1000 degrees Celsius, coated with glaze and then sent for a second glaze-firing at a temperature of about 1300 degrees Celsius, or greater. In an alternative method of glazing particularly associated with Chinese and early European porcelains the glaze was applied to the unfired body and the two fired together in a single operation.
Categories of porcelain
Western porcelain is generally divided into the three main categories of hard-paste, soft-paste and bone china, depending on the composition of the paste (the paste is the material used to form the body of a piece of porcelain).
Hard paste
One of the earliest European porcelains was produced at the Meissen factory and was componded from china clay kaolin, quartz and alabaster and was fired at temperatures in excess of 1350-degrees Celsius to produce a porcelain of great hardness and strength. China clay, feldspar and quartz (or other forms of silica) continue to this day to provide the basic ingredients for most continental European hard paste porcelains.
Soft paste
Its history dates from the early attempts by European potters to replicate Chinese porcelain by using mixtures of china clay and ground-up glass or frit;
Bone china
Although originally developed in England to compete with imported porcelain Bone china is now made worldwide. It has been suggested that a misunderstanding of an account of porcelain manufacture in China given by a Jesuit missionary was responsible for the first attempts to use bone-ash as an ingredient of Western porcelain (in China, china clay was sometimes described as forming the bones of the paste, while the flesh was provided by refined porcelain stone). For what ever reason, when it was first tried it was found that adding bone-ash to the paste produced a white, strong, translucent porcelain. Traditionally English bone china was made from two parts of bone-ash, one part of china clay kaolin and one part of Cornish china stone (a feldspathic rock), although this has largely been replaced by feldspars from non-UK sources
History
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The earliest porcelains originated in China possibly during the Eastern Han dynasty (25-220 AD). Chinese experts emphasise the presence of a significant proportion of porcelain-building minerals (china clay, porcelain stone or a combination of both) as an important factor in defining porcelain and shards recovered from Eastern Han kiln sites in Zhejiang, estimated to have been fired at a temperature of between 1260 to 1300 degrees Celsius, were found that met this condition (He Li 1996).
East Asian ceramics
Korean pottery Chinese porcelain Yixing clay Imari porcelain Japanese potteryEuropean porcelain
Porcelain was first made in China, and it is a measure of the esteem in which the exported Chinese porcelains of the seventeenth and eighteenth centuries were held in Europe that in English China became a commonly used synonym for the Franco-Italian term porcelain. After a number of false starts, such as the so-called Medici porcelain, the European search for the secret of porcelain manufacture achieved success in 1708 with the discovery by Ehrenfried Walther von Tschirnhaus assisted by Johann Friedrich Böttger of a combination of ingredients, including Colditz clay (a type of kaolin), calcined alabaster and quartz, that proved to be suitable for making a hard, white, translucent porcelain, first produced at Meissen. It appears that in this discovery technology transfer from the Orient played no part: Chinese porcelain itself provided the mute stimulus. Tschirnhaus had a wide knowledge of European science and had also worked on the search for porcelain for more than a decade. Imprisoned by Augustus as an incentive to hasten research, Böttger was obliged to work with other alchemists in the futile search for transmutation, but his work in this area ended in 1705, when he was appointed to assist Tschirnhaus in the search for the secret of making porcelain.
A workshop note records that the first specimen of hard, white European porcelain was produced in January, 1708. It was left to Böttger to report to Augustus in March, 1709 that he could make good, white porcelain and for this reason credit for the European discovery of porcelain is traditionally given to him, but unjustly, in the view of many of those who point to the essential role played by Tschirnhaus.
The Meissen factory was established in 1710, following the development of a kiln and a glaze suitable for use with Böttger's porcelain, which required firing at very high temperatures to achieve translucence (greater than 1350 degrees Celsius). Schmidt was the creative force behind KT&K's famed Lotus Ware, commonly acknowledged to be the finest porcelain ever produced in the United States.
In unusual modern cases porcelain has also been used as a building material for exterior surfaces. An older example is the Gulf Building, Houston, Texas, built in 1929, which had a seventy-foot long logo of porcelain
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