Raku is an ancient firing method originating in early sixteenth century Japan. The first firing (bisque) is done as you would any other piece of clay.  Glaze is then applied to all the areas that are white and the dark areas are left un-glazed.  The piece is then returned to the kiln for the glaze firing.  Once the piece becomes molten (1750 degrees) it is removed from the kiln using metal tongs.  The piece is then placed in a metal container filled with combustible material such as leaves or straw which will immediately ignite.  A lid is placed on the container, trapping the smoke inside which creates the subtle grays and blacks.  The sudden and severe temperature change causes the cracks on the glazed areas.