The Yanpu 硯史 "A history of inkslabs" is a short history of the inkslab compiled by the Song period 宋 (960-1279) painter and calligrapher Mi Fu 米芾. The book begins with a paragraph on how inkslabs are used (Yongpin 用品) and ends with a short appendix on the quality of inkslabs (Xingpin 性品) discussing the softness and hardness of the stone. The chapter "Models" (Yangpin 樣品) explains the different character of inkslabs during the Jin 晉 (265-420), Tang 唐 (618-907) and Song periods. The book lists 26 famous types of stones, from jade to the white stone of Caizhou 蔡州. The stones from the prefectures Duan (Duanyan 端硯) and She (Sheyan 歙硯) are rated as the best. The author stresses that he personally has seen all the stones described, and he does only write on those he has seen himself. He also describes two ancient inkslabs of his own collection, the Qingcui dieshi 青翠迭石 and Zhengzishi 正紫石, which are both rare antiques. His book is very reliable and can be trusted as the judgment of a real expert.
The Yanshi is included in the collectanea Baichuan xuehai 百川學海, Shuofu 說郛, Xuejin taoyuan 學津討原, Qunfang qingwan 群芳清玩, Siku quanshu 四庫全書 and Meishu congshu 美術叢書.
Source: Li Xueqin 李學勤, Lü Wenyu 呂文鬰 (1996). Siku da cidian 四庫大辭典, vol. 2, p. 1853. Changchun: Jilin daxue chubanshe.