Page 22 - Decorative Arts, Part II: Far Eastern Ceramics and Paintings, Persian and Indian Rugs and Carpets

CHINESE CERAMIC TECHNIQUES

ANY VARIABLES DETERMINE the appearance of a ceramic vessel. Of these the most important are the
chemical structure of the clay body and glaze, the firing temperature, and the atmosphere of the kiln.
M Chinese potters were early masters of these variables: In prehistory they developed the wheel used
for throwing clay; they used a high-fired, hard glaze as early as the fifteenth century B.C.; and they were the first
to use colorants in their glazes. Owing to the demands of the court, aristocrats, and literati for greater perfection
in ceramics, by the Song dynasty (A.D. 960-1279) Chinese potters had mastered the manipulation of clays, glazes,
and kiln atmospheres to create an astonishing variety of visual effects.

TYPES OF CERAMIC BODIES AND METHODS OF FORMATION
The Chinese ceramics in the National Gallery include examples of the three main categories of clay body: earthen-
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ware, proto-porcelain or stoneware, and porcelain. Of these, earthenware has the longest history in China, extend-
ing back well into the Neolithic period (5000-2000 B.C.). Earthenware can be made from a variety of common clays.
The versatile clay body has good plasticity and is suitable for handbuilt, molded, and wheel-thrown ware. Generally
fired at temperatures between 800 and 1,100 degrees C, it is porous unless glazed. A clear demarcation results
between glaze layer and clay body because low firing temperatures hinder their physical integration. Although the
fired body is weaker than ware fired at higher temperatures, it is also less brittle. A high iron content allows a low fir-
ing temperature and contributes to a range of warm colors of earthenware from buff to brown and black. A good
example of an earthenware vessel with a green lead glaze is one from the Liao dynasty (916-1125) (1972.43.2).
Stoneware is considerably harder than earthenware. When fired it becomes partially vitrified, or
glasslike, and so is impermeable to water. The body is composed of a variety of plastic clays whose colors range
from brown to gray. The malleability of the clay body makes it especially suitable for wheel-thrown ware. A high-
er firing temperature, between 1,200 and 1,300 degrees C., encourages a strong chemical and physical bond
between the glaze and the body.
The collection includes several stoneware vessels, including the Yaozhou celadon bowl (1972.43.3) and
the Jian-ware tea bowl (1972.43.4), which date to the twelfth and thirteenth centuries. The celadon bowl, from
Shaanxi Province in northwest China, has a gray stoneware body over which a transparent green glaze contain-
ing a small amount of iron oxide has been applied. The Jian-ware tea bowl, from south-coastal China, has a dark
brown, iron-rich body that typically contains approximately eight percent iron oxide, and a glaze that contains
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about five to eight percent iron oxide. Some very fine high-fired Chinese stoneware so closely approaches porce-
lain in characteristics that Western writers often classify it as "porcellanous."
Most of the Chinese ceramics in the National Gallery are of porcelain, the basic materials of which first
appeared in China as early as the Eastern Han dynasty (A.D. 25-220). The porcelain body is often a combination
of kaolin, feldspar, and flint or quartz. Kaolin is a naturally white clay (resulting from a low iron content) whose
high alumina content gives it a high melting point (above 1,800 degrees C.). The addition of the mineral feldspar
acts as a flux to lower the melting point. Flint or quartz is added to minimize warpage and to add strength. A
mixture derived solely from these ingredients lacks elasticity and is difficult to manipulate, but the addition of a
more plastic, iron-rich clay creates a workable body, although some concession must be made to whiteness. 3
Porcelain is the least tolerant of the ceramic bodies—it shrinks very little so tends to warp more readily.

6 D E C O R A T I V E A R T S