I recently acquired this oribe bowl by Japanese potter, Tetsuya Kowari. Isn't it wonderful? The glaze combines so beautifully with the rough texture of the clay, and inside the dark glaze has pooled, creating these amazing crystals and rainbow-like colour effects. I had no idea that crystals could form like this in a copper glaze. I'm guessing it requires very slow cooling to create them.
Kowari-san also produces fabulous anagama-fired, ash-glazed pieces. More of his work can be seen here at the Naganawa Gallery: http://shop.yumetenpo.jp/goods/goodsList.jsp?st=naganawa.jp&category=11:5&action=category