Due to the wealth of different ceramics created throughout the ages, the line between pottery and porcelain is often unclear in China, as the term (Ciqi) that actually means porcelain is used indisciminately for both china porcelain and pottery items, including those that are really predecessors to real porcelain.
Below is a clear definition from a Chinese source to what should be considered pottery and what is porcelain among Chinese antique ceramics.
Glazed Ming storage jar.
Needless to say that when speaking of porcelain the border between the two is often muddled by the fact that low-fired white clay was used in antique pottery like the Tang Sancai wares, and that the clay of early Ming ceramics is often not white. In China these are usually also called porcelain, especially those having a body covered by white slip or underglaze blue decoration.
The above mentioned Tang Sancai or Sancai wares were often made of white clay, but they were fired at a lower temperature than normally porcelain would be. Therefore, it is doubtful whether it should not fall under the pottery category, according to the table below.
Some of the green/greenish glazed pottery wares (Celadon) are also frequently called porcelain (Qingci) in Chinese, when they actually should be classified as glazed pottery. On the other hand, Longquan ceramics are often categorized as porcelain. Their clay is actually light gray. Some people use a simple way of categorizing ceramics: any ceramic body of high density with a high ringing tone is categorized as porcelain.
Differences between pottery and porcelain
Pottery
Porcelain
Material
normal clay
Kaolin (china clay)
Color
red, brown, gray
white
Firing temperature
600-800°
1200° or more
Properties
relatively porous & soft
non-porous, hard & strong
Tapping sound
dull sound
clear ring
Water absorbtion
high
very low or none
Body
non-transparent
semi-transparent
Characteristics
low chemical & mechanical resistance
high chemical & mechanical resistance
* This definition may differ in Europe due to the existence of "soft paste" porcelain, bone china and different clays prior to the discovery of Kaolin.
Ceramic separation by age, in China Worth mentioning here is a separation of ceramics according to age, as used in China. Many collectors in China make a difference between so-called "ancient" ceramics and "antique" or old ceramics. Normally, ancient ceramics are those before the Song dynasty, but most collectors will include Song and Yuan ceramics in this category, whether they are porcelain or pottery. The latter means mainly Ming and Qing dynasty ceramics, but occasionally includes Song and Yuan dynasty decorated porcelain as well.
The actual time of discovery/development of real porcelain is not quite clear, but Kaolin seems to have been in use at least since the Tang dynasty. However, Chinese folklore attributes the discovery of Kaolin clay to the Song dynasty, which is also known for the first decorated porcelain.
Experienced Chinese collectors often specialize in either the ancient pottery ceramics, or in porcelain from and after the Song dynasty and later. Theye feel that the field of knowledge required in Chinese ceramics is really much too broad to allow for expertise in all.
Separation according to plain and decorated ceramics Sometimes ceramics are separated in yet another way, namely by periods of plain and decorated ceramics. The time before the Ming dynasty is called the 'plain ceramics period', while the Ming and Qing dynasties and later is called the 'decorated ceramics period'. Before the Ming dynasty the majority of ceramics had no color decoration painted either under or on top of the glaze, thus they are called 'plain'.
