Six-and-One Mud ( 六一泥 Liuyi Ni ), also called Divine Mud or Medical Mud, and also Divine Glue for Consolidation and Strengthening ( 固濟神膠藥泥 Guji Shen Jiao Yaonu ), is the mud used in outer alchemy to consolidate and strengthen the containers. The so-called Six-and-One comes from the numerology of Book of Changes. According to the River Chart ( 河圖 Hetu ) numerology of the Book of Changes ( 《周易》 Zhouyi ), the numbers from 1 to 10 lie respectively in different directions. 1 and 6 lie in the north with 1 as the Heavenly Number ( 天數 Tianshu) and 6 as the Earthly Number ( 地數 Dishu ). The idea "The Heavenly 1 originates Water and the Earthly 6 completes it" is the explanation of matching in this type of numerology. Daoist alchemists, absorbing the numerology of the Book of Changes and holding that the outer alchemist process must correspond with the heavenly and earthly numbers, select the mud of the "6 and 1" kinds of components. According to the Yellow Emperor's Book of the Divine Elixir of the Nine Cauldrons ( 《黃帝九鼎神丹經》 Huangdi Jiuding Shendan Jing ), the composition of Six-and-One Mud is: alum, salt, alkali, oyster, steatite, etc. the manufacturing process is: first burn the former four kinds of components for 20 days, pound the latter with a pestle thirty thousand times, mix them with bitter wine of brewed for 100 days. The mud thus obtained can be used for consolidating the cinnabar containers with a thickness of 3cm to 5cm. The container consolidated with the mud is usable after only 100 days of drying under the sun.
Originally used in outer alchemy, the mud was also adopted in inner alchemy. The Explanation of the Medicine Mirror of Master Cui in the Great Compilation of the Golden Elixir ( 《金丹大成集•解注崔公入藥鏡》 Jindan Dacheng Ji Jie Cuigong Ruyao Jing ) of Xiao Tingzhi in the Yuan Dynasty contains the idea of "consolidating with Six-and-One Mud". In inner alchemy, Six-and-One Mud symbolizes the consolidation of the Divine Chamber ( 神室 Shenshi ) and keeping essence and vital breath from leaking.