 The main tool, from both a ritual and a technical point of view, is the crucible. To reproduce the state of the cosmos at its inception (hundun; see §4.3), the vessel should be hermetically sealed so that the vital “breath” (qi) is not dispersed. Under these conditions, the elixir ingredients “revert” (huan) to their original state. This refined matter is equated with the Essence (jing) that is hidden within the Dao and gives birth to the world (“Vague and indistinct! Within it there is something. Dim and obscure! Within it there is an essence”; Daode jing, sec. 21). The elixir therefore is a tangible sign of the seed that generates the cosmos.