The Cauldron

It may "represent the fifth element of Spirit and the Mystic Center."

An iron pot, a receptacle in which poisons, ointments and philtres were brewed.

Also;

linked to fertility, abundance and revival of the dead by ancient Celts.   

Human sacrifice - throats of victims slit, blood drained into bowl (Babylon, Mayan, Inca, Aztec...)    

Norse God, Odin, drank magic blood from a cauldron of wisdom to obtain divine power.    

Greek myth tells of witch goddess, Medea, who used it to restore a person's youth. 

Contemporary Witches use them for burning fires and incense.

In rituals, they would be placed 'on the witches' altar inside the magic circle.

As a vessel, it is feminine symbol and is associated with the womb of the "Mother goddess."