Raku is an ancient technique of firing clay, the roots of which go back to 16th century Japan. Unlike other glaze firings where the kiln is slowly brought up to temperature and then allowed to cool slowly, raku is fired very quickly--from room temperature to 1850 and back to room temperature in about an hour. When the kiln has reached the correct temperature, it is opened, the pieces are removed using long tongs, placed in a pit lined with sawdust, and quickly covered with a metal pot or container that is lined with straw. The combustibles use up the oxygen in the container, producing beautiful metallic colors. The unglazed areas of the pot absorb carbon from the burning organic matter and become black. In the close up, you can see something that only exists (to my knowledge) in raku--preserved fire. The pattern of colors is not the result of different glazes. It is the result of the pattern of the flames interacting with the glaze. This process DOES NOT create a waterproof vessel. It is decorative only.