Stoneware and Porcelain, A Great Tradition
High-fired ceramics are of great antiquity, dating back to about 500 B.C. in China. Prior to this time, all pottery the world over was earthenware, that is, porous, nonvitrified ware. The origins of the early stonewares of China are lost in the obscurity of time, and we can only conjecture as to how they came to be made and as to the techniques employed.
At the time of the appearance of the first hard and vitrified pottery in China, the Chinese potters were technically far behind the potters of the ancient Near East, and it is surprising that hard stonewares were not made first in Persia. Glazed ware had been made in the Near East for hundreds of years, and the control of color and texture was far in advance of that achieved by the Chinese. It is hard for us now to realize what a difficult thing it must have been to achieve a range of glaze colors which included green from copper, yellows and browns from iron, blue from cobalt, and purple from manganese. All these colors had to be refined from natural minerals and mixed and blended with the glaze ingredients without the benefit of any exact knowledge of mineralogy or chemistry. It is no wonder that the old potters guarded their secrets jealously, and passed them down from one generation to the next. Firing, too, was a technique which could only have been worked out over a long period of trial and error, and some of the achievements of the potters of the Near East in the pre-Christian era, such as the massive architectural reliefs in glazed the of the Assyrians, are evidence of a high degree of control over firing temperature and atmosphere.
Several factors may have prevented the development of higher temperature wares in the Near East. One factor is that the design and construction of kilns remained at a relatively primitive level. The typical kiln throughout the Near East was a simple updraft chamber, fed through one or more fire mouths around the base and vented through a short chimney at the top. The flames from the wood or brush fires traveled upward through the ware, which was protected by saggers. Judging from present-day kilns still in use in the area, the walls of the kilns were made of a clay similar to that from which the pottery was fashioned, and were insulated with mud or dirt on the outside.
Although such kilns were adequate for the firing of low-temperature earthenwares and lead and alkaline glazes, they were not well designed for the full utilization of the heat from the fuel, and the higher temperatures could not be obtained in them. Moreover, the materials used in constructing the kilns were not very refractory, and even if temperatures in excess of 1100°C could have been