From this description, Wang Kuo-tsai learned that yangnao paper was made by applying a coating to ciqing paper, and required the use of sheep's brain and "flue-top soot," which is carbon black taken from the very top of the flue, where the soot particles are the finest.
從這段敘述，王國財得知羊腦箋是用磁青紙作為塗佈原紙，另外還需要羊腦和頂煙墨，也就是煙道（排煙管）最頂端收集的碳黑，其粒子最細。