The Kuan kilns were operated by the Sung imperial court in present day Kaifeng and Hangchou. At the beginning, their limited output was intended exclusively for the court. With its high iron content, Kuan clay is dark while its thick translucent glaze is a subtle pale blue-gray. A distinguishing feature of this refined ware is the crackle pattern of its glaze, which was purposely induced during the cooling process. The crackled glazes undoubtedly appealed to the refined antiquarian taste of the scholar class as well as the Sung court. Kuan ware was grouped by later connoisseurs as one of the five so-called "official court wares" of the Sung dynasty. Like Lung-ch'uan celadon, Kuan ware was greatly admired by the Ch'ing court during the eighteenth century and it was imitated in porcelain at the imperial workshops at Ching-te-chen.