The passion for Chinese culture during the Nara period of the eighth century led to a brief fling with Tang Chinese-style three-color glazed wares among the imitative Japanese aristocracy; but these seem to have been too much at odds with native instincts, for they were soon forgotten. After the government moved to Kyoto and launched the Heian era, both the indigenous pottery techniques--the low-fired, brown, porous pots for the common people and the high-fired, gray, polished bowls for the aristocracy--continued to thrive side by side. However, technical advances in the high-firing kilns brought about subtle changes in the mock-glazes of the aristocratic wares. It was discovered that if they were fired in an atmosphere where there was abundant oxygen, the fused particles of fueled ash on the surface would turn amber, whereas if oxygen was excluded from the kiln, the surface ash would fuse to a pastel green. Thus by varying the baking process, Heian potters could produce a variety of light colors, creating a pottery considerably more delicate than had been possible before. Aside from this refined technique for firing, however, the Japanese steadfastly refused to change their traditional methods of making pots. For this reason, Japanese ceramics were deliberately kept at a technically primitive stage until the early part of the thirteenth century while the Chinese were making considerable advances in the art. During the years from the ninth to the thirteenth century, while the Japanese isolated themselves from the mainland, the Sung Chinese were learning of new glazes far more subtle and refined than those employed during the T'ang. In the early years of the thirteenth century, when Japanese monks journeyed to China to study the new faith of Zen, they were dazzled by the sophisticated new Chinese wares they encountered. Through the offices of Zen a second revolution in Japanese ceramics occurred. The instrument for this second revolution (according to tradition) was the priest Dogen, founder of Japanese Soto Zen, who on one of his trips to China was accompanied by a Japanese potter known as Toshiro. Toshiro stayed in China for six years, studying the Sung techniques of glazing, and on his return he opened a kiln at Seto, where he began copying Sung glazed wares. Although he has been called the father of modem Japanese ceramics, his attempts to duplicate the highly praised Sung products were not entirely successful. Furthermore, the wares he did produce, decorative and thick-glazed, found no acceptance except among the aristocracy and priesthood, both of whom favored Seto wares for the new pastime of drinking Chinese tea. But while the Zen aesthetes and tea drinkers amused themselves with Seto's fake Sung celadons, the commoners continued to use unglazed stoneware.