Although Celadon is the term for a translucent crackle glaze applied to porcelain and stoneware, it has come to mean wares that are specifically greenish blue or gray in color, particularly those from China and Korea. The trademark greenish hues of celadon wares were achieved through the use of clays and glazes that contained small amounts of iron, which turns green in a reduction firing atmosphere. (When there is insufficient oxygen in the air in a kiln, oxygen molecules are pulled from the ceramics themselves; it is this change in chemical composition that changes the color of the ware.) The thickness of the glaze and type of clay determine the color after firing, and getting the “right” effect is extremely difficult. The thin watery glaze runs off high points in the design and pools in impressions, creating dazzling gradations in color, especially in incised and molded designs.
Jade was prized in East Asia, and the ability to imitate its color in porcelain was highly valued. In the Goryeo Period (918-1392) in Korea, a celadon ewer or teacup was more precious than gold or silver. The high estimation of celadon was not limited to Korea, but extended to discerning connoisseurs at the court of the Northern Song dynasty (960–1127) in China. Celadon was quite popular in Japan as well, where it was both imported and manufactured in a native version. Celadon is considered by many to have reached its height during the Goryeo period, and these wares continue to be prized by collectors today.