One of the characteristic excavated items from the Sui to Tang dynasty is the circular inkstones. There are two types of circular inkstones: one with ring under the legs supporting the inkstone surface, and one without. Tokiwayama Bunko has three white porcelain circular inkstones and one copper-green glazed inkstone, but all of those are the former type.　
According to the excavated materials so far, the excavated areas are different for those without ring and those with ring, the former being in Anyang in Henan province and the latter in Xi’an in Shaanxi province and Guyuan in Ningxia Hui Autonomous Region. Around the end of the 6th century, those without ring first appeared in Anyang, Henan Province, and later in the 7th century during the Sui dynasty, those with ring began to appear in Shaanxi Province. Concerning the copper-green glazed miniature circular inkstone, there is an example excavated from the tomb in Nigxia in the late 7th century.

Publications
*The Bulletin of the Chinese Ceramic Study Association of Tokiwayama Bunko Foundation vol.7 Early White Porcelain, Tokiwayama Bunko Foundation, 2018 (see commentary by Sarah Sato)