We've had some questions from customers lately about different categories of ceramics as they relate to teaware, and thought it might be useful to post a few guidelines. The history of Chinese ceramics and tea are closely intertwined, as many ceramic forms evolved to facilitate brewing tea. Porcelain was invented in China and Western scientists and artisans labored for centuries to duplicate it. They didn't start to get the knack until the 18th century.
A fair amount of present-day confusion occurs because (as often happens) Western and Chinese categories of ceramics don't match up. Chinese think of tao (陶), often translated "pottery" and generally comprising what in English would be called either stoneware or earthenware; and ci (瓷), usually translated "porcelain." Tao are less vitreous ceramics fired at lower temperatures, while ci signifies high-fired, more vitreous products that make a distinctive ringing tone when struck. Adding to the complexity, Chinese like to modify these generic nouns to add clarity, so they speak, for example, of bai ci (white porcelain), qing ci (celadon porcelain), and tao qi (tao ware). A general term for ceramics in Chinese is tao ci.
As usual, our Western definitions are more precise, with three broad categories. Here "porcelain" is high-fired and vitreous, with a white body. In addition, what's sometimes known as "true porcelain" is thin-bodied and translucent. True porcelain is contrasted with what's called simply "china," which also has a white body but is softer and heavier than true porcelain and, unlike it, can be cut with a file (not that this is a test you'd typically want to try on your favorite porcelain!).
Porcelain's impermeability means it's airtight, so it can be used to store loose tea. It won't absorb the essence of liquids it contains, therefore it's ideal for gaiwans, pitchers, teacups, and other teaware you may wish to use with multiple varieties of tea. Also, the thin body means it loses heat quickly, a desireable trait when you're brewing temperature-sensitive tea. Like other ceramics, porcelain may be glazed to decorate or strengthen the object, or left unglazed (bisque). When porcelain is glazed, the glaze is often clear to highlight its unique translucent character.
The second Western category, stoneware, is also high-fired and very hard, but only semi-vitreous with a heavier, opaque, colored body (often brown or gray). Yi xing teapots are an example of unglazed stoneware, whose slightly porous nature allows those pots to absorb the essence of tea that's brewed within. Stoneware's thicker body also helps to retain heat.
Finally, there's earthenware, which is fired at lower temperatures and is non-vitreous. Earthenware is made from clay with less silica, the substance that vitrifies during firing, so it's relatively soft and absorbent unless glazed. It has an opaque body that's easy to scratch, chip, or break. An inexpensive terracotta flowerpot is an example of unglazed earthenware, which generally isn't used for teaware.
Like tea, ceramics reward a lifetime of study. There are many fabrication techniques (molding, sculpting, throwing on a wheel); glazing, firing, and decoration options; clay additives; and other characteristics that skilled artisans can manipulate. Writing from the tea perspective, we can only say that ceramics and tea complement one another superbly, and knowledge and appreciation of one is sure to motivate interest in the other.