This domestic ware was in such demand that a class of professional potters came into being--inevitably leading to a gradual falling off of the individualistic character of the pots, as craftsmen began to mass- produce what had previously been a personal art form. The Korean Buddhist culture which reached Japan in the fifth and sixth centuries brought the Japanese new techniques for high-firing their stoneware pots, introducing a process whereby ashes from the kiln were allowed to adhere to the surface of a piece to produce a natural glaze. These new high-temperature pots had a hard surface texture and an ashen- gray color, while the existing native wares of low-fired porous clays retained their natural brown hues. Typically the average Japanese preferred the natural-colored, soft clay vessels, and so the two types of pottery continued to be produced side by side for several hundred years, with the aristocracy choosing the hard-surfaced mainland-style gray works and the common people continuing to use the simpler, underrated brown vessels, which were often fashioned by hand. The importance of this instinctive Japanese reaction for the later acceptance of Zen-inspired ceramic art cannot be over-stressed. Not only did the Japanese love of natural clay make them reject glazes for centuries after they had learned the necessary techniques, they also seem to have had little spontaneous interest in decorating their pots or using high-firing or mechanized techniques for their production, perhaps because the technology came between man and object, distancing the potter too far from his handiwork. Japanese potters cherished their regional individuality, and they continued to express their personal sensibilities in their work, so there were a multiplicity of rural kilns and a wide variety of styles.