The Ru kiln located in Linru County of Central China's Henan Province represented another major celadon school that rose in northern China in the Song Dynasty (960-1279). Ru Kiln refers to a government kiln in Linru County catering to the Northern Song rulers; the kiln's products were known as Ru ware porcelain.
Notes in an Old Scholar's Studioby Lu You, the famous Song poet, records the emergence of Ru ware: "The Northern Song rulers, considering the white porcelain vessels of Dingzhou unsuitable for use because of their rough mouth-rims, sent personnel to establish porcelain kilns in Ruzhou to manufacture celadon. In the eyes of the people of the Song Dynasty, the celadon of Ru ware ranked first in quality among all northern celadon ware."
The Ru kilns supported the vessels with studs (thin pieces of material used for supporting objects) during firing so that their mouth-rims and even their foot-rims were entirely covered with a layer of smooth vitreous (glasslike) glaze. Ru ware porcelain had a thick lustrous green glaze with a sapphire-like blue tinge. The vessels had fine crackles (decoration patterns of very small surface cracks) over the entire surface.
In making celadon at the Ru kilns, the amount of iron in the raw materials and the reduction flame were carefully controlled, demonstrating maturity in Chinese celadon manufacture.
A kiln for baking celadon and also Jun ware porcelain vessels were found in Pingliangsi of Baofeng in Henan Province. Many believed it was a site of the Song Dynasty's government-run kiln, but this is yet to confirmed as many of the products that have been found there so far are just ordinary celadon vessels and light sky-blue glaze porcelain vessels with a green tinge, of which few measure up to Ru Kiln standards.