During the Han Dynasty, potters learned how to build increasingly efficient kilns. The tunnel kiln was developed which was capable of reaching the higher temperatures necessary to fire stoneware clays (generally considered to be above 2000° F). This higher firing temperature results in a greater fusion of the clay body, a process called vitrification (literally, to become a glass). Stoneware clays are typically gray to brown in color, and have a greater 'hardness' than earthenware, and moreover, are not porous after firing, meaning stoneware vessels do not leak.
The ash acts as a flux, lowering the melting temperature of the clay surface slightly, and producing a 'self glazing' effect in the kiln. Colors produced are very 'natural' and recall the colors of many minerals, which of course were produced in nature under similar heated conditions (volcanic or igneous rock).
Material 材質：Clay 陶土
Size 尺寸：h19 / w21 cm
Country 國家：Han Dynasty, China 中國 漢時代
Year of Issue 年份：206 B.C. - A.D. 220