Yixing teapots are fired from Yixing clay. The clay for the pots comes from the city of Yixing in the eastern Chinese province of Jiangsu. The traditional use of Yixing teapots dates back to the the Song Dynasty (960 - 1279). Yixing wares were commonly exported to Europe from the 17th century on. They are known as Zisha ware. The color of Zisha ware is red, brown or purple and is unglazed.
The term "yixing clay" is often used as an umbrella term to describe several distinct types of clay used to make stoneware:
- Zhusha or Zhu Ni (朱砂 or 朱泥; literally, "cinnabar sand/clay"): reddish brown stoneware with a very high iron content. The name only refers to the sometimes bright red hue of cinnabar (朱砂; pinyin: zhūshā). There are currently 10 mines still producing Zhu Ni. However, due to the increasing demand for Yixing stoneware, Zhu Ni is now in very limited quantities. Zhu Ni clay is not to be confused with Hong Ni (红泥, literally, "red clay"), another red clay.
- Duan Ni (鍛泥; literally, "fortified clay"): stoneware that was formulated using various stones and minerals in addition to Zi Ni or Zhu Ni clay. This results in various textures and colours, ranging from beige, blue, and green (绿泥), to black.
The raw materials for yixing clay are buried deep underground, sometimes under heavy sedimentary rock formations. When excavated, it is usually located within stratified layers of other clays. The seam of yixing zisha can be as thick as a several decimeters, up to a meter. Yixing clays consist of fine iron-containing silt, with mica, kaolinite and varying quantities of quartz and iron ores as its main mineral constituents.
Processing of raw zisha yixing clay involves removing the clay from the underlying strata, drying it under the sun in open stalls, and then pulverizing the dried clay pieces into fine particles. The clay powder then undergoes air screening to isolate clay particles of the finest grit size. The screened clay is then mixed with water in a cement mixer to a thick paste, piled into heaps, and vacuum processed to remove air bubbles, in addition to some moisture from the clay mixture. The quality and quantity of water in yixing clay is critical in that it determines the quality of the stoneware products produced. After this processing, the resulting clay is then ready to be used.
The appearance of yixing products, such as its colour or texture, can be enriched and altered through the addition of various metal oxides into the yixing clay, through the manipulation of firing temperatures, and also from regulating the kiln atmosphere (oxidative versus reductive).
Yixing teapots are meant for use with black, oolong teas or puer tea. The teapots absorb a tiny amount of tea and will develop a coating. This why only hot water and no soap should be used to clean the teapots. Yixing teapot are usually used only for one type of tea because it could influence the flavor. They are smaller than typical teapots and usually, a bigger amount of tea leaves is used which are infused several times.
Early pots were designed for travel use hence you will see the simple classical look of the pots produced during the Ming Dynasty. Most tea drinking enthusiast will have one teapot for travel use, these tend to be less expensive and compact in design. It was not until during the mid-Qing Dynasty (18th century) that tea connoisseurs started to use the pot at home and the artisan begin to form them into different shape and sizes. Many exotic forms were conceived. Vessels were decorated with poetic inscriptions, calligraphy, paintings and seals were incised onto the surface of the teapots.