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Water-grinding
水飞 〔水飛〕shuǐ fēi
Fine grinding of medicinal materials in water.
Method: The materials are first roughly crushed. They are then placed in a porcelain mortar, covered with water, and ground until the grating sound of rough lumps ceases. At this point, more water is mixed in, and the water that contains suspended particles is poured off and reserved. More water and materials are added to the mortar, and the process is repeated. The reserved suspension is allowed to stand until the particles have settled, and the excess water is poured off. The remaining sludge is sun-dried, after which it is ready for use. This method is used for minerals and shells. Its advantage over dry grinding is that fine particles do not blow away or get lost, and that impurities dissolved in the water are (at least partly) removed. The much finer power it produces makes for greater assimilation of orally taken medicinals and reduces irritation in topical applications. Cinnabar (Cinnabaris,