With lines of silver breaking through a black laquer surface, the tenmoku pottery of Koji Kamada conjures images of the unknown universe. Visitors to an exhibition at Akasaka Yu Gallery celebrating Kamada's 30-year career have a rare opportunity to see masterpieces made by Japan's leading tenmoku potter.

Kamada's works give an impression of depth that's like being swallowed up in space. Colored dark blue, black and silver, they resemble stars exploding in the night sky or reflections of sunlight on a deep-blue sea.

"This is what fascinates me about tenmoku pottery," says Kamada. "When I look at these pieces, I see the sky, beautiful with sparkling stars, or a deep, mysterious galaxy."

This kind of pottery can be traced back to the Sung Dynasty (960-1279) in China, and the technique is thought to have reached Japan in the Muromachi Period (1338-1573) when Japanese Zen priests brought back a shiny chawan teabowl from a temple on China's Mount Tienmu. The Japanese reading of Tienmu -- Tenmoku -- gave the style its name.

Tenmoku's distinctive appearance comes from its glaze of yuyaku, a lacquerlike substance containing 5-7 percent iron. "The iron in yuyaku gives the pottery its unique metallic shine," says Kamada. "In the kiln, it melts and bubbles, and when the bubbles burst, the yuyaku crystallizes into all sorts of patterns."

There are various types of tenmoku, with the two leading styles being yohen tenmoku and yuteki tenmoku, both patterned with those crystallized bubbles (yuteki) that create external patterns. On yuteki tenmoku ware, individual bubbles are discernible. Yohen tenmoku, the rarer form, has larger markings formed from clusters of yuteki, with each cluster shining with rainbowlike brilliance.

"It is extremely difficult to get the exact pattern you want," says Kamada. "Even the slightest change in the temperature of the kiln or the amount of iron could transform the pattern and sometimes even change the color of the piece."

Historically, tenmoku pottery has been used to make only chawan. Just four early examples exist, dating from the 12th-13th centuries, and three of these are designated national treasures.

The paucity of early examples, and the technical difficulties of the process, made it famously hard for potters to create tenmoku pieces. Kamada, however, has taken both the traditional form and the techniques one step further. Aside from chawan, he makes vases, tableware, incense burners and even tokkuri (sake bottles).

Not only that, but he has also created his own genres of tenmoku, one of which he has dubbed ginsho (silver-crystal) tenmoku. In this process, the piece is so thickly coated with silver yuteki that the bubbles can hardly be discerned, making the pottery appear metallic.

"The challenge is not to make a copy," says Kamada. "It is to express your originality. Innovating provides a great opportunity to be original, because there are no prior examples. With my work I have challenged the art world, and I shall continue to do so as long as I am an artist."