These tiles get their irridescent effect from an ancient Japanese firing process called Raku. During the process, the artist places the glazed piece into a very hot kiln. It remains in the kiln for anywhere from twenty minutes to one hour or until the glazed surface appears melted. While still red hot, the piece is removed from the kiln and put in a bed of sawdust which then bursts into flame. After it cools a bit, it is immersed in cool water.
When cooled, the piece is washed with steel wool to bring out the full brilliance of the surface color.
It is the unique nature of this process that results in flashes of copper luster for which the raku method is known. Because of the random nature of this technique each piece will be special and one of a kind.