Porcelain
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Wikipedia-Article "Porcelain"
Porcelain is a hard ceramic material. It is fired at a higher temperature than that used to fire glazed earthenware and stoneware pottery. It is white or off-white in colour, translucent and can be decorated to provide additional colour. Porcelain is made by firing a mixture of materials including China clay and China stone in a kiln at temperatures in the region of 1200 to 1350 degrees Celsius. The resulting material is hard, strong, glassy and durable, but also brittle. The main components of porcelain, China clay (kaolinite) and crushed China stone (a form of feldspar) are found in nature and result from the weathering and decomposition of igneous rocks such as granite and basalt.
Clays used for the manufacture of porcelain can be specially formulated to provide high-strength and high-durability. It is also possible to blend clays to obtain a clay body that is ideal for throwing on a potter's wheel. A wide range of porcelain clays is readily available from many specialist suppliers of materials for ceramics.
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Techniques
Porcelain wares may be formed by moulding, by hand-building and in the case of round-wares, by throwing on a potter's wheel. Porcelain ware was produced on the potter's wheel in many historic cultures, including China and Japan. Porcelain has many industrial uses and is also employed to form wares ranging from everyday household crockery to objects of fine art. Many categories of glazes, e.g. celadons, were formulated specifically for their striking effects on porcelain. Modern potters also produce porcelain ware, and generally believe these clay bodies challenge production, firing and glazing skills.
From the perspective of the potter the most noticeable difference between porcelain clay and other pottery clays is that it wets very quickly (small changes in its moisture content can produce large changes in its plasticity) and that it tends to continue to 'move' for longer than other clays, requiring experience in handling to attain optimum results.
Porcelain wares are usually coated with a layer of glaze and are often decorated with coloured enamels. As a rule porcelain ware of all types is typically bisque-fired at around 1000 degrees Celsius (1800 degrees Fahrenheit), and then glaze-fired (the final firing) at 1300°C (2300°F) or higher, though it should be noted that Chinese porcelain is an exception to this rule.
Chinese porcelain
Chinese ceramic wares are often classified as being either northern or southern. Present day China comprises two separate, and from the geological point of view, distinctly different, land masses: the northern and the southern. The two land masses were brought together by the action of continental drift, forming a junction that lies very approximately along the line of the present-day Yangtze river. Geological differences between the northern and the southern land masses have influenced the nature of the ceramic wares made in the two areas and, for example, in the north ceramic wares tend to have bodies made using mainly China clay, in the south ceramic wares tend to have bodies made using mainly China stone. In turn, this led to the development of coal-fuelled kilns suitable for the high-temperature firing of clay-rich wares in the north and wood-fuelled kilns more suitable for the lower-temperature firing of the stone-rich southern wares.
Chinese porcelain is made from kaolin and a form of feldspar called petuntse. In the Western tradition ceramics are primarily divided into the categories of earthenware, stoneware or porcelain, depending upon the composition of the body material and the temperature at which the ware matures into a stable crystaline matrix. The Chinese tradition recognises only two primary categories of ceramic, high-fired (ci) and low-fired (tao). This can lead to confusion because, for example, in China no distinction is drawn between high-fired stonewares and porcelain. One important result of this is that the property of translucence carries no weight in the traditional Chinese classification of ceramics. An unusual characteristic of Chinese porcelain is that in the main it is green-fired or once-fired, which is to say that the body and the glaze are fired together. After the body of a piece is formed and finished it is air-dried, coated with a glaze, dried again and fired. In the high temperature of the kiln the body and the glaze are fused together to become one unit. Chinese enamelled wares are also produced in this way, but the enamels are added after the first, high-temperature, firing and the pieces are sent for a second firing in a smaller, lower-temperature kiln.
The city of Jingdezhen has been an important centre for the production of ceramics in southern China since at least the early Han Dynasty. The early wares were low-fired but by the time of the Southern and Northern Dynasties (420 to 589) locally available raw materials were being used to produce a form of porcelain. In the year 1004, under the Song emperor Jingde, the newly re-named city of Jingdezhen was established as a centre for the production of imperial porcelain.
Detailed descriptions of the manufacture of porcelain at Jingdezhen during the Qing dynasty exist, including, from the European perspective, the letters of Père d'Entrecolles and from the Chinese perspective, a memoir written by Tang Ying. Two letters written by Père Francois Xavier d'Entrecolles, a Jesuit missionary (and industrial spy) who lived and worked in Jingdezhen described in detail the methods and materials used in the manufacture of porcelain wares in the later years of the reign of the Kangxi emperor; an important period in the history of Chinese ceramics. In his first letter, dated 1712, d'Entrecolles describes the way in which China stone was crushed, refined and formed into little white bricks known in Chinese as petuntse or baidunzi. He then goes on to describe the refining of China clay, kaolin or Gaoling, the preparation of glazes, the stages of forming porcelain wares, glazing and firing. Père d'Entrecolles, explaining his motives for describing what he had seen at Jingdezhen, states that "Nothing but my curiosity could ever have prompted me to such researches, but it appears to me that a minute description of all that concerns this kind of work might, somehow, be useful in Europe" but in the event his first letter came too late to be of much help in the European search for the secret of making porcelain. In 1743, during the reign of the Qianlong emperor, Tang Ying, the imperial supervisor at Jingdezhen produced a memoir entitled "Twenty illustrations of the manufacture of porcelain." Unfortunately, the original illustrations have been lost but the text of the memoir may be found here, together with photographs replacing the missing illustrations and an additional commentary.
History
In the context of Chinese ceramics the term porcelain lacks a universally accepted definition. This in turn has led to confusion about when the first Chinese porcelain was made. Claims have been made for the late Eastern Han period (100 to 200 AD) the Three Kingdoms period (220 to 280 AD) the Six Dynasties period (220 to 589 AD) and the Tang dynasty (618 to 906 AD). A strong body of Chinese scholarly opinion is currently of the view that the first true porcelain was made in the Chinese province of Zhejiang during the Eastern Han period, but this opinion is controversial. However, Chinese experts emphasise the presence of a significant proportion of feldspathic minerals 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 to meet this condition.
During the Sui and Tang periods (581 to 906) a wide range of ceramics, low-fired and high-fired, were produced. These included the well-known Tang lead-glazed sancai (three-colour) wares, the high-firing, lime-glazed Yue celadon wares and low-fired wares from Changsha. In northern China, high-fired, translucent porcelains were made at kilns in the provinces of Henan and Hebei.
During the Song and Yuan dynasties porcelain was made at Jingdezhen and other kiln sites in southern China using crushed and refined China stone alone, but by the early eighteenth century China clay was being added to the China stone, in about equal proportions. Porcelain bodies made from China stone fire at a lower temperature, in the region of 1200 degrees Celsius, than those made with a mixture of China clay and China stone, which require firing in the region of 1350 degrees Celsius. China clay when added to the body material produced a porcelain of great whiteness and of great strength. Whiteness, in particular, was a much sought after property of porcelain, especially that used for blue and white wares.
Some notable Chinese porcelain wares
Qingbai wares. Qingbai wares were made at Jingdezhen and at many other southern kilns from the time of the Northern Song until their almost complete eclipse, starting early in the fourteenth century, by underglaze-decorated blue and white wares. The qingbai glaze is a porcelain glaze, so-called because it was made using China stone, an important constituent of the porcelain body. The qingbai glaze is clear, but contains iron in small amounts. When applied over a white porcelain body the glaze produces a greenish-blue colour that gives the glaze its name (qingbai in Chinese means greenish-blue). Bowls, some with incised or moulded decoration and varying from the everyday to more finely made pieces represent the overwhelming bulk of surviving qingbai wares.
The Song dynasty qingbai bowl illustrated was probably made at the Jingdezhen village of Hutian, which was also the site of the Imperial kilns established in the year 1004. The bowl has incised decoration, probably representing clouds or the reflection of clouds in the water. The body is white, translucent and has the texture of very fine sugar, indicating that it was made using crushed and refined China stone, rather than a mixture of China stone and China clay. The glaze and the body of the bowl would have been fired together, in a sagger, in a large, wood-burning dragon-kiln or climbing-kiln typical of southern kilns of the period. Though not the case with the bowl illustrated, many Song and Yuan qingbai bowls were fired upside down in special segmented saggers, a technique first developed at the Ding kilns in Hebei province. The rims of such wares were left unglazed but were often bound with bands of silver, copper or lead.
Blue and white wares. Following in the tradition of earlier qingbai porcelains, blue and white wares are glazed using a transparent porcelain glaze. The blue decoration is painted onto the body of the porcelain before glazing, using very finely ground cobalt oxide mixed with water. After the decoration has been applied the pieces are glazed and fired.
It is believed that underglaze blue and white porcelain was first made in the Tang dynasty. No complete piece of Tang blue and white is known to exist, but shards dating to the eighth or ninth century have been unearthed at Yangzhou in Jiangsu province. It has been suggested that the shards originated from a kiln in the province of Henan. In 1957 excavations at the site of a pagoda in the province Zhejiang uncovered a Northern Song bowl decorated with underglaze blue and further fragments have since been discovered at the same site. In 1970 a small fragment of a blue and white bowl, also dated to the eleventh century, was also excavated in the province of Zhejiang. In 1975 shards decorated with underglaze blue were excavated at a kiln site in Jiangxi and, in the same year, an underglaze blue and white urn was excavated from a tomb dated to the year 1319, in the province of Jiangsu. It is of interest to note that a Yuan funerary urn decorated with underglaze blue and underglaze red and dated 1338 is still in the Chinese taste, even though by this time the large-scale production of blue and white porcelain in the Yuan, Mongol, taste had started at Jingdezhen.
Starting early in the fourteenth century, blue and white wares rapidly became the main product of Jingdezhen, reaching the height of its technical excellence during the later years of the reign of the Kangxi emperor and continuing in present times to be an important product of the city.
The tea caddy illustrated shows many of the characteristics of blue and white porcelain produced during the Kangxi period. The translucent body showing through the clear glaze is of great whiteness and the cobalt decoration, applied in many layers, is of a fine blue hue. The decoration, a sage in a landscape of lakes and mountains with blazed rocks is typical of the period. The potting is good and the porcelain body is finely textured, indicating the presence of a significant proportion of China clay in the paste. The piece would have been fired in a sagger (a lidded ceramic box intended to protect the piece from kiln debris, smoke and cinders during firing) in a reducing atmosphere in a wood-burning egg-shaped kiln, at a temperature approaching 1350 degrees Celsius.
Fakes and reproductions
Chinese potters have a long tradition of borrowing design and decorative features from earlier wares. Whilst ceramics with features thus borrowed might sometimes pose problems of provenance, they would not generally be regarded as either reproductions or fakes. However, fakes and reproductions have also been made at many times during the long history of Chinese ceramics and continue to be made today in ever-increasing numbers. A few examples of fakes and reproductions are given below
- Reproductions of Song dynasty Lonquan celadon wares were made Jingdezhen in the early eighteenth century, but outright fakes were also made there, using special clay and artificially aged by boiling in meat broth, refiring and storage in sewers. Père d'Entrecolles records that by this means the wares could be passed off as being hundreds of years old.
- At Jingdezhen the two remaining wood fired, egg-shaped kilns produce convincing reproductions of earlier wares and at Zhejiang province good reproductions of Song Longquan celedon wares continue to be made in large, side-stoked dragon kilns.
- Before World War II, the English potter Bernard Leach found what he took to be genuine Song dynasty cizhou rice-bowls being sold very cheaply on the dock of a Chinese port and was suprised to learn that they were in fact freshly made.
- In modern times the market for Song dynasty Jian tea-bowls has been severely depressed by the appearence in large numbers of modern fakes good enough to deceive even expert collectors. It is reported that some of these fakes show evidence of having had genuine Song dynasty iron-foot bases grafted onto newly made bodies.
- In the late nineteenth century fakes of Kangxi period famille noire wares were made that were convincing enough to deceive the experts of the day. Many of these pieces may still be seen in museums today, as may pieces of genuine Kangxi porcelain decorated in the late nineteenth century with famille noire enamels. A body of modern expert opinion holds that porcelain decorated with famille noire enamels was not made at all during the Kangxi period, though this view is disputed.
- A fashion for Kangxi period blue and white wares grew to large proportions in Europe during the later years of the nineteenth century and triggered the production at Jingdezhen of large quantities of porcelain wares that looked back to the ceramics of the earlier period. These blue and white wares were not fakes, or even convincing reproductions, even though some pieces carried four-character Kangxi reign marks that continue to cause confusion to this day.
The value of testing in the authentication of Chinese porcelain is disputed. The most widely-known test, the thermoluminescence test (TL-test) can be used to provide an estimate, within very wide limits, of the date of last firing. The test is carried out on small samples of porcelain drilled or cut from the body of a piece, which can be risky and disfiguring and for this reason the test is rarely used for dating finely-potted, high-fired ceramics. Spectroscopy can be used to determine the composition of glazes, for comparison with the results of analyses carried out on reference specimens of known provenance.
See also
- Tangshan, Hebei province
- Canton porcelain
- Chinese export porcelain
- Dehua porcelain factories
- Blanc-de-Chine
- Famille jaune, noire, rose, verte
- Swatow ware
- Yixing clay
- Kraak porcelain
Japanese porcelain
European porcelain
Porcelain was first made in China and it is a measure of the esteem in which the Chinese export porcelains of the seventeenth and eighteenth centuries were held in Europe that china became a commonly used synonym for the term porcelain. After a number of false starts the European search for the secret of porcelain manufacture ended in 1708 with the discovery by Johann Friedrich Böttger (1682 to 1719) of a combination of ingredients, including kaolin, suitable for making a hard, white, translucent porcelain. It appears that this discovery was one in which technology transfer from the Orient played little if any part.
Böttger worked at Dresden and at Meissen, in the German state of Saxony, for the highly eccentric Elector, Augustus the Strong (1670 to 1733). After training, as an apprentice pharmacist, he turned to alchemy and it was his claim that he knew the secret of transmuting dross into gold that attracted the attention of Augustus, whose own talent for performing the exact opposite of this operation was very well developed. Imprisoned by Augustus as an incentive to hasten research, Böttger was obliged to work with other alchemists in the futile search for transmutation. Fortunately for Böttger, Augustus was an enthusiastic collector of Oriental porcelain and at some point during Böttger's fruitless endeavours ordered that a switch be made from the search for gold to a method of making white gold, or porcelain. In this, at least, Böttger was sucessful.
The Europeans used a soft paste, which makes for weaker porcelain than the Chinese method. To compensate, around 1750 the English began to use calcined bone ash to strengthen their porcelain, with the resulting material (typically comprising 25% to 50% bone ash) becoming known as bone china.
Key people and places
- Gzhel, Russia
- Oranienbaum, Russia
- Dmitry Ivanovich Vinogradov
- Josiah Wedgwood
- Limoges, France
- Lladro, Spain
- Meißen, Germany
- Herend, Hungary
- Pécs, Hungary
- Porsgrunn, Norway
- Sèvres, France
- Worcester, England
- Delft, Netherlands
References
- Hamer, Frank and Janet (Third Edition, 1991). The Potter's Dictionary of Materials and Techniques., A & C Black Publishers, Limited, London, England. ISBN 0-8122-3112-0.
External links
Chinese Porcelain:
- Chinese porcelain at the Lady Lever Art Gallery
- Jingdezhen attractions
- Jingdezhen: Ceramics Metropolis of China
- Jingdezhen Special Folk Arts Porcelain Research Institute
Porcelain - general