Raku firing, an ancient Japanese firing method. One method with glazed pieces involves removing it from the kiln where its glowing hot, setting it in a can full of combustible material, setting it on fire then starving it of oxygen.
Another raku style is the horsehair method. It also is removed from the kiln. While it is still hot, thick horse hairs, sugar, and feathers are placed on the pot so they burn in various directions. 
Raku pots will only hold dried foliage, it cannot hold water.