This bottle has been fired with a copper turquoise glaze. You can see the distinctive crackle patterning that happens with the Raku process. These pieces are truly individual as the crackle patterning is unique on each and every pot. As the glaze suffers thermal shock when it is plunged into cold sawdust the resulting carbon penetrates that crackled surface. It is sealed in as the pot shrinks as it rapidly cools leaving distinctive black crackle patterning within the glaze surface.