China:The Glorious Tang And Song Dynasties - Asian Art Museum ...

THE PORCELAIN INDUSTRY
As with the industries of printing and paper making, the Tang and Song dynasties supported important
industrial advances in pottery manufacture. The origin of porcelain pottery-making technology
dates back 6000 years to the Neolithic period, and the related technologies and skills were continuously
developed throughout early Chinese history. During the Tang, a systematic approach to the
industry of pottery making marked a spectacular increase in quantity and quality of work. Porcelain
kilns were constructed all over the country and improvements were instituted in nearly every aspect
of production. By the time the industry had matured during the Song, porcelain was an indispensable
item for daily use in all sectors of society and was exported by land and sea. By the eleventh century,
it was being shipped to Japan, India, Arabia, Turkey, and Africa. The Portuguese began
exporting porcelain directly to Western Europe in the sixteenth century, and by the late seventeenth
century Europeans had developed a passion for porcelain “china.” Chinese artisans succeeded in
keeping the technology for porcelain production secret from Europeans for two hundred years.
Even after successful industrial espionage led to the rise of a European porcelain industry in the
early eighteenth century, Chinese porcelain remained a popular import item.
PORCELAIN MANUFACTURE
Porcelain base is made from a combination of porcelain clay, orthoclase, and quartz. The external
surface of a porcelain base is coated with vitreous glaze and the base is baked in a porcelain kiln at
1200°C. The finished porcelain, after the baking process, has a very low water absorption coefficient
(below 0.004) and is extremely hard. In addition to these practical strengths, porcelain is
highly valued because of its beautiful glaze. Glazing is divided into two groups: underglaze and
overglaze. Underglaze is applied to the porcelain base before it is baked. Overglaze is applied after
the porcelain base is baked, when it is then rebaked with the glaze.
Glaze created from a combination of mineral substances was originally invented in the Shang
and Zhou dynasties (eleventh to tenth centuries BCE). The glazes produced in ancient China were
generally green in color, until the Sui dynasty (581–618) when white glaze was first created.
Manipulation of minerals to produce various colors can be observed in the use of iron in glaze production.
Iron has two oxides: ferrous oxide (green color) and ferric oxide (dark brown or terracotta
color). Iron in the glaze transforms into ferrous oxide when the baking process is a reduction reaction,
and into ferric oxide when the baking process is an oxidization reaction. The final color of finished
porcelain is determined by the percentage of iron in the glaze. The finished glaze is light green
if the content of iron in the glaze is below 0.8%, and dark green if the iron is over 0.8%. When iron
content exceeds 5%, the glaze will be dark brown or nearly black. The same principle applies similarly
to other color agents. In the Tang dynasty, the porcelain industry was classified into green
porcelains, mainly in north China, and white porcelains, mainly in south China.
During the Song dynasty, comprehensive improvements were achieved in almost every aspect of
the porcelain production cycle. The whole manufacturing process was standardized into several
working procedures including base-making, glazing, ingredient control, and temperature maintenance.
Each procedure was supervised by a specialist. In addition the industry was divided into five
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