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An extremely rare early Ming copper-red glazed shallow dish. Xuande six-character mark within double-circles and of the period (1426-1435). Photo: Christie's Images Ltd., 2010

The rounded sides rising from a slightly tapering ring foot to a slightly flared rim, covered inside and out with a bubble-suffused glaze of even vibrant cherry-red tone below the white rim, the base covered with a transparent glaze; 8 in. (20.2 cm.) diam., box  Estimate HK$2,500,000 - HK$3,500,000  Price Realized HK$7,220,000 ($933,548)

Notes: One of the most widely admired glazes in the history of Chinese porcelain production is the rich copper-red glaze seen on this Xuande dish. Successfully fired copper-red-glazed porcelains from the early 15th century, like the current example, are especially favored by connoisseurs, due to the combination of colour and texture of the glaze. Not only is this a particularly beautiful glaze, it is also rare, since successful firing of this copper-red glaze was extremely difficult. This is demonstrated by two dishes excavated from the Xuande strata at the site of the Imperial kiln in 1982 illustrated in Xuande Imperial Porcelain excavated at Jingdezhen, Chang Foundation, Taipei, 1998, pp. 93-4 and 265-6, nos. 95-1 and 95-2. On the larger of these excavated dishes the glaze has fired a different colour in different parts of the dish, and on the smaller excavated dish the glaze over the whole dish, except for its white base, has an unattractive greyish-tone. The aim would have been to produce dishes with a rich cherry-red glaze, such as the current example.

Monochrome copper-red glazes on Jingdezhen porcelain appear to have first appeared in extremely small numbers during the Yuan dynasty, but a clear, brilliant red does not appear to have been achieved. Even in the Hongwu reign (1368-1398) of the Ming dynasty, when renewed efforts appear to have been made by the potters to improve copper red, the glazes tended to be semi-opaque and to have a somewhat waxy sheen to their surface. They also failed to reach a good colour, and instead varied from an orangey-red to a muddy brownish-pink

In the early 15th century, however, renewed efforts were made at the Imperial kilns to produce a fine copper-red glaze, such as that seen on the current dish. They appear to have made significant changes to the base glaze, which improved the colour of the red. There seem to have been three changes made to the base glazes previously used. The potters slightly increased the calcium content, so that the glaze was nearer to the normal lime-alkali glaze used for underglaze blue porcelains. This made the glaze a little more fluid at high temperatures, allowing more bubbles to escape and also allowing more of the batch material in the glaze to dissolve. Both techniques added to clarity of the glaze, although there were still enough bubbles left to create the wonderful curdled texture characteristic of these glazes, which can clearly be seen on the current dish.

The potters also found that if they reduced the amount of copper in the glaze it created a purer red colour, since too much copper tends to make the glazes look rather muddy, and they changed from using oxidized copper metal to using oxidized bronze. The tiny traces of tin, lead and antimony present in the oxidized bronze seem to have encouraged the reduction of the copper (Cu+) ions to colloidal copper metal during the cooling process, which helped to enhance the red colour. In addition, the Xuande potters at the imperial kilns discovered that the red glazes were most successful when fired to a slightly higher temperature - about 1300oC - slightly over the normal 1250-1280. Thus the potters of the early 15th century managed, at last, to produce rich cherry-red glazes, that are often called xianhong or 'fresh red', on porcelains, such as the current example, which remain the most sought-after of all copper-red wares.

It is also noteworthy that following the Hongwu Emperors edict of 1369, requiring that porcelain vessels should be used on the Imperial Altars, red-glazed porcelains came to be used on the Chaoritan, the Altar of the Sun, and hence the glaze on some of these copper-red vessels is called jihong, sacrificial red. Of course, as well as its use in ritual, the colour red is associated in China with happiness and celebration. A small number of Xuande copper-red dishes are preserved in the Chinese palace collections. One such dish in the collection of the Palace Museum, Beijing, which has no reign mark on the base, but retains very faint traces of gilded designs on both exterior and interior is illustrated in Monochrome Porcelain, The Complete Collection of Treasures of the Palace Museum, vol. 37 Hong Kong, 1999, p. 11, no. 9. Two dishes very similar to the current example were included in an exhibition of Xuande porcelains at the National Palace Museum, Taipei, and are illustrated in Catalogue of the Special Exhibition of Selected Hsuan-te Imperial Porcelains of the Ming Dynasty, Taipei, 1998, pp. 390-1, no. 168 and pp. 394-5, no. 170. The first of these Taipei dishes bears a six-character underglaze blue Xuande mark on its white-glazed base, while the second bears an incised six-character Xuande mark. Another similar copper-red dish in the collection of the Percival David Foundation bears a six-character underglaze-blue reign mark on its base. Other larger copper-red-glazed dishes with blue and white Xuande marks, one illustrated in Porcelains from the Tianjin Municipal Museum, Hong Kong, 1993, pl. 80; one in the Shanghai Museum, illustrated in Chugoku Rekidai Toji Ten, Tokyo, 1984, pl. 75; one in the Metropolitan Museum of Art, New York, illustrated in Oriental Ceramics, Kodansha Series, vol. 11, Tokyo, 1982, no. 70; and another recovered from the site of the imperial kilns was included in the exhibition Imperial Porcelain of the Yongle and Xuande Periods Excavated from the Site of the Ming Imperial Factory at Jingdezhen, Hong Kong Museum of Art, 1989, illustrated in the Catalogue, no. 70.

Further examples with incised Xuande marks include one from the Edward T. Chow Collection, sold at Sotheby's Hong Kong, 25 November 1980, lot 52; and another from the Winkworth Collection is illustrated by A. Joseph, Ming Porcelain: The Origins and Development, London, 1971, pl. 99.

Christie's. Important Chinese Ceramics and Works of Art, 1 December 2010, Hong Kong www.christies.com