Page 25 - Decorative Arts, Part II: Far Eastern Ceramics and Paintings, Persian and Indian Rugs and Carpets

temperature lead glazes produce the brighter colors, although a wide color range is characteristic of these glazes.
An oxidizing atmosphere is always indicated, since lead oxide readily reduces to metallic lead.
In alkaline glazes sodium, potassium, or lithium acts as a flux. Depending on certain ingredients, they
may be opaque or transparent. Particularly intense colors can be produced in an alkaline matrix; cobalt oxide
yields the familiar deep blue, and copper oxide produces shades of turquoise, blue, and red.
The lower temperature glazes are represented in the collection by the copper lead-silicate enamel on the
apple-green pieces. This enamel was applied over an already high-fired glazed body, and refired at a much lower
temperature. Low-fired enamel color, used here to create a continuous monochrome effect, is more often used
for overglaze painting on polychrome porcelain.
High-fired glazes, with maturation temperatures above 1,200 degrees C., are compatible with stoneware
and porcelain. Often more subtle in color and texture, these glazes tend to be less complicated in formulation
than those used for low-fired ware. High-fired glazes have the advantage of great durability and chemical resis-
tance. In cross-section, there is little differentiation between glaze layer and body.
While many high-fired glazes are formulated around feldspar, recent scholarship has shown that the min-
eral was not the major component in Chinese glazes. Rather, there appear to be two main types of high-fired glazes:
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lime and lime-alkali glazes. Certain colorants, such as copper, iron, and cobalt, can withstand high temperatures,
though more subdued colors generally result, as in the example of the celadon green produced by iron oxide.

METHODS OF PORCELAIN DECORATION
By the Ming (1368-1644) and Qing (1644-1911) dynasties (the periods most strongly represented in the National
Gallery collection) there were three primary methods used for porcelain decoration. The first involved covering
the entire surface of an unfired vessel (with the exception of the foot-ring) with a monochrome glaze. A combi-
nation of alkali, alumina, and silica was often used, and was usually applied by dipping. The glazed vessel was
then subjected to a single firing. This technique, seemingly simple, was in actuality remarkably complex because
of the demands of producing the ingredients for the brilliantly colored glazes. The period of technical perfection
in this method of decoration came in the Qing dynasty, during the reigns of the Kangxi (1662-1722), Yongzheng
(1723-1735), and Qianlong (1736-1795) emperors. The National Gallery's Widener collection includes superb
groups of apple-green, celadon, oxblood, pale blue, peachbloom, and white vessels.
The second method of decoration involved applying underglaze colors directly onto the surface of the
unfired porcelain body. Cobalt, iron, and copper oxide pigments could withstand the high-firing temperatures
and were fritted with glaze materials to discourage the color from migrating. When first painted on the leather-
hard porcelain body, the cobalt oxide was dark brown. When the pigment dried, the vessel was covered with a
clear glaze and subjected to a single high-firing; only in the heat of the kiln did the brilliant blue color appear. 10
The use of cobalt oxide as an underglaze colorant is first seen on earthenware during the Tang dynasty
(618-907). Its application is evident on a series of tenth-century bowls with underglaze blue flowers discovered
at a Yangzhou excavation, as well as on sherds of blue-and-white ware excavated from twelfth- and thirteenth-
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century pagodas in Zhejiang Province. There was a surge in production of blue-and-white porcelains during
the Yuan dynasty (1271-1368). During this time the kilns at Jingdezhen, the great porcelain kiln center in Jiangxi
Province, were placed under imperial patronage by Kublai Khan (r. 1280-1294) for the purpose of creating tens
of thousands of such porcelains to be used as imperial tributes, particularly to West Asia where blue-and-whites
were favored. The early Ming porcelain stem bowl in the Steele collection (1972.43.5) represents a classical phase
of blue-and-white porcelain production in the reign of the emperor Xuande (1426-1435). 12
Underglaze painting in copper oxide pigment was found occasionally in the fourteenth century, but less
often than the popular underglaze blue decoration. The red that resulted from reduction firing was often grayish,

C E R A M I C T E C H N I Q U E S Q