All this changed dramatically around the middle of the sixteenth century with the rise of an urban middle class and the sudden popularity of the Zen tea ceremony among this new bourgeoisie. Zen, which had brought Chinese glazes to Japan in the thirteenth century, sparked the emergence of a brilliant era of glazed ceramic art in the sixteenth. No longer content with primitive stoneware or reproductions of Chinese vessels, the potters of Japan finally developed native styles at once uniquely Japanese and as sophisticated as any the world has seen. It was another triumph for Zen culture. Rural kilns with long traditions of stoneware water vessels converted to the production of tea-ceremony wares, and throughout the land the search was on for colored glazes. The craze reached such heights that the shogun generals Nobunaga and Hideyoshi rewarded their successful military commanders not with decorations but with some particularly coveted tea-ceremony utensils. Although ceramic tea caddies and water jars were required for the ceremony, the real emphasis was on the drinking bowl, for this was the piece that was handled and admired at close range. A proper bowl, in addition to being beautiful, had to be large enough and deep enough to allow sufficient tea for three or four drinkers to be whisked; it had no handle and consequently had to be of a light, porous, nonconducting clay with a thick, rough glaze to act as a further insulator and to permit safe handling between drinkers; the rim had to be thick and tilted slightly inward, to provide the participants with a pleasant sensation while drinking and to minimize dripping. In other words, these bowls were as functionally specialized in their own way as a brandy snifter or a champagne glass of today. A number of styles of tea bowl developed during the sixteenth century, reflecting the artistic visions of various regional potters and the different clays available. What these bowls had in common, beyond their essential functional characteristics, was an adherence to the specialized dictates of Zen aesthetic theory. Equally important, they were a tribute to the historic Japanese reverence for natural clay. Even though they were glazed, portions of the underlying clay texture were often allowed to show through, and the overall impression was that the glaze was used to emphasize the texture of the underlying clay, not disguise it. The colors of the glazes were natural and organic, not hard and artificial.