 As a type of hard ceramic material, Porcelain 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.
Chinese porcelain is made from kaolin and a form of feldspar called petuntse. The Chinese tradition recognises only two primary categories of ceramic, high-fired ( ci 瓷 ) and low-fired ( tao 陶 ). 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 is 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 ( 景德镇 ) has been an important centre for the production of ceramics in southern China since at least the early Han Dynasty ( 汉朝 ). The early wares were low-fired but by the time of the Southern and Northern Dynasties ( 南北朝 )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.
 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 ( 浙江 ) 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 ( 河南 ) and Hebei ( 河北 ) .
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.
Following in the tradition of earlier qingbai porcelains ( 青白瓷 ) , blue and white wares are glazed using a transparent porcelain glaze, so called because it is made using highly-refined China stone fluxed with lime to reduce its melting point. 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. |
