One of the “Five Great Kilns,” Jun stonewares with their thick, lavender-blue glaze and areas of purple and violet were formerly known in the West as “Clair de Lune” and came from the Henan province. As of today, over a hundred kiln sites have been discovered. Some specialised in producing porcelain ware for the Imperial courts, with a history dating back to the Tang Dynasty. According to tradition they were mainly manufactured under the Northern Song Dynasty at Yangzhe which under the Jin Dynasty was renamed Junzhou. The name “Junuao” only appears in Chinese texts in the Ming period; for this reason some experts have reservations about the dating. However, the excavations at Jungzhou in 1964 have established that Jun ware appeared in the Song period with increased manufacture during the Jin period.
The signature look of Jun ware are the grey or buff-coloured stonewares with their turbid glaze. They were first biscuit fired at a low temperature, then covered with a ferruginous slip and several layers of glaze containing rice stalk ash, which is rich in silica. After a second firing at a higher temperature, the surface of the piece becomes rough, pitted with little “v” or “y” – shaped cracks. Through the microscope, little bubbles of silica suspended in the glaze are visible. The opalescent effect of the surface is created by light playing on these imperfectly vitrified particles and the irregular surface through the thickness of the glaze.
By using copper oxide as pigment, the Jun kilns successfully produced copper-red glaze in reducing conditions. This was a breakthrough in ceramic technology. Use of copper oxide as colouring agent was technically difficult, as the chemical components in the basic glaze, the temperature, and the atmosphere were all very sensitive factors. Even the slightest deviations from the method resulted in an undesirable shade of red.
There are also some Jun ware pieces, with the glazing varying from lavender on the inside to violet purple on the outside. The outside is sometimes streaked like fur. The base is glazed in brown; a carved number varying from 1 to 10 is visible on the bottom. It is not known exactly what the numbers signify – either a serial number or indication of size. Round the bottom there are also numerous spur marks from the kiln. The numbered pieces seem to be from the Jin period. However, some numbered pieces have been found in the Song kilns in the course of recent excavations. Other Jun ware, with heavy, less highly fired body called ma-jun in Japan, belong to the Yuan period,
Jun ware vessels such as flower pots, cauldrons, and writing-brush basins were all modelled after ancient bronze vessels used for rituals. There were similarities between Jun ware and those of Guan, Ru and other kilns of the same time period, because they were all intended for serving the courts. Flowers and floral patterns were the fashionable form of decoration for porcelain at the time. However, Jun ware did not use decorative patterns, but the vessels themselves came in the shapes of flowers. Common shapes were flowerpots, flat bowls, and writing-brush washbasins in the shape of Chinese crab-apple flowers, lotus flowers and pot bases made to resemble sunflowers. The latter are a truly unique feature of Jun ware.
Of the Five Great Kilns of the Song Dynasty, aside from Ding ware which had engraved or imprinted patterns as decorations, the kilns all produced undecorated porcelain. Of course this absence of ornamentation did not result in bland wares; rather it was a reliance on natural forms. The Ge, Guan and Ru kilns all produced celadon, and all three utilized crackle glaze as a form of decoration. The crackle glaze was caused by different degrees of contraction in different parts of the glaze. Thus when fired, the surface of the glaze would begin to crack. This may originally been an imperfection of the firing technology. However, porcelain artisans were able to take advantage of this defect and make it a decorative element.