Qing-dynasty writer Shen Chu (d. 1799) gives a very complete description in his Xi Qing Biji (" West Qing Notes "):" Yangnao paper is made using Xuande ciqing paper. Sheep's brain and flue-top soot are mixed together and stored in a cellar. After a long time the mixture is taken and smeared onto the paper, and rubbed smooth with a stone to make writing paper.
清朝沈初在《西清筆記》對此有相當完整的描述：「羊腦箋以宣德磁青紙為之，以羊腦和頂煙墨窨藏，久之取以塗紙，砑光成箋。