YUYAN SHUWU FOUR-CHARACTER HALL MARK IN BLACK ENAMEL, QIANLONG/JIAQING PERIOD (1736-1820)

Yuyan Shuwu, 'The Library of Washing Inkstone', is a hall mark used in the Yongzheng and Qianlong periods. A set of four blue and white and copper-red wine cups with this mark but written in underglaze-blue were sold at Christie's New York, 15-16 September 2011, lot 1529.