Porcelain has been in use for over 4000 years and is a hard, white translucent ceramic which has been baked to the ultimate degree of compactness. When sounded acoustically it generates an even ring.
Porcelain was first recognised in China at the time of the Tang dynasty (618-907) and is formed from the fusion of Kaolin, a brilliant white unmeltable alumnium hydrosilicate, and soft feldspar from petuntse -white quartz-, at a temperature of between 1300-1400 degrees Celsius. Porcelain exists in two forms known as hard paste and soft paste porcelain respectively. The European hard paste variety was discovered by the alchemist Johann Bottger and closely resembles Chinese porcelain. As a consequence of Bottger's discovery, Augustus II of Poland founded the Meissen factory in 1710.
There are a couple different ways in which porcelain items are decorated. The most common today is molded, decorated, and glazed. Others are molded and enameled then fired again. The third type is under glaze in blue and red. The Chinese have always been extremely proficient at porcelain work, and have produced numerous pieces that look like coral, glass, stone, and many other materials.
What's it worth? Take a look at this Porcelain price guide: sold listings for a value indication.