TONGZHI-GUANGXU PERIOD (1862-1908), CHUXIUGONG ZHI FOUR-CHARACTER SEAL MARK IN UNDERGLAZE BLUE

See a nearly identical example in the collection of Nanjing Museum, published in Imperial Kiln Porcelain of Qing Dynasty- Gems of Collections in Nanjing Museum, Shenzhen, 1998, p. 51, no. 49.