Understanding Ceramics. Porcelain vs. Bone China vs. Pottery.
The best place to begin this informative essay is answering the baseline question: What is a ceramic?
Ceramics are classified as inorganic and non-metallic solids which permanently change when heated. The resulting products have a range of useful properties, including extraordinary hardness and strength, extremely high melting points, and good electrical and thermal insulation. Ceramics are generally made by first mixing variations of clay, earthen elements, powders, and water. The mixture is then shaped into the desired form before firing in high-temperature kilns (ovens) until hard. Typically, ceramics are covered in decorative, waterproof, paint-like glazes. While there are numerous types of ceramics, the best-known are pottery, glass, porcelain, brick, and cement.
Once humans discovered that clay could be dug up and formed into objects by first mixing with water and then firing, the ceramic industry began and is considered one of the oldest technologies and art forms in the world. Archeologists have uncovered ceramics dating back to at least 24,000 BC. Animal and human figurines, slabs, and balls are the earliest ceramic forms unearthed. Made of animal fat and bone mixed with bone ash and fine clay which was then fired in kilns dug into the ground, experts are unsure what many of them they were used for. Utilitarian pottery vessels for storage date to 9000 BC.
Glass, experts believe, was discovered accidentally by the Egyptians around 8000 BC. This was the result of sand combined with soda (and other chemical processes) reacting to overheated kilns producing a colored glaze on the pottery. The effect was beautiful and thereafter purposefully created and perfected, however, not until 1500 BC would glass be produced independently of clay-based ceramics and fashioned into separate items.
Over the centuries, the technology and applications of ceramics have steadily increased. Classifying and describing ceramics in all the variations, chemical compositions, and manufacturing processes is now involved and immensely complicated. Honestly, I have minimal interest in the fine distinctions and technicalities of ceramics as a whole! Instead, I shall sum up the history of ceramics by noting that the leap from natural materials to synthetic materials with better resistance to high temperatures was developed in the 16th century, and with the later burst of technology during the Industrial Revolution, ceramic manufacture advanced to the industrial scale.
PORCELAIN & BONE CHINA ~
An important advancement in ceramics came in the form of porcelain. The development of porcelain began in China during the T’ang Dynasty in 600 BC. Chinese potters combined white kaolin clay with petuntse (a type of rock with a high content of mica and feldspathic minerals) which was then biscuit-fired at a low temperature before being heated to an incredibly high temperature (1,300°C, or 2,372°F). This distinctive method creates a ceramic that is so hard and tough that it can be fashioned into vitreous (glass-like) vessels with walls so thin they can be translucent.
(noun) – 1530s, from Middle French porcelaine> and directly from 13th century Italian porcellana> “porcelain” literally “cowrie shell.”
To expand upon the above, the name porcelain derived from the chinaware’s lustrous transparency resembling the shiny surface of the cowry shell (a sea snail). Reaching further back, etymology-wise, the cowry (or cowrie) shell in the Italian is porcellana from the Latin porcellus> “young pig or piglet.” According to an old theory, the connection between the shell and the pig is a perceived resemblance of the shell’s opening to the exposed outer genitalia of pigs. Oh-kay!
The porcelain process was perfected during the Ming dynasty, famous for its blue and white porcelain. In the 9th century AD, porcelain was introduced to the Arab world and during the Crusades was brought to Spain. From there it spread throughout Europe. By the 1500s, the term “chinaware” had become synonymous with porcelain.
The slideshow below contains a very small sampling of antique porcelain.
Many other countries attempted to reproduce porcelain, including England. These lesser quality pseudo-porcelains (so to speak) usually utilized ground glass and are not as hard but still a fine ceramic with their own unique properties and artistry. The best of these porcelain-like ceramics is bone china, which was invented in England by Thomas Frye in 1748. Bone china has a composition similar to that of porcelain, but at least fifty-percent of the material is finely powdered bone ash mixed with china stone (also called Cornish or Cornwall stone). China stone is a feldspar-rich mineral with mica, fluorospar, quartz and other granite-derived minerals such as kaolinite, making it similar to petuntse but lacking the iron-bearing minerals. As the ceramic most akin to pure porcelain, bone china is strong and can be formed into dishes with very thin, translucent walls.
In 1767, Josiah Spode established his business in Stoke-on-Kent and began mixing ox bone ash with kaolin and Chinese stone. His formula for bone china is the hardest of them all, Spode’s creation described as the single most significant development in the history of this specific industry. Most famously, perhaps, is the bone china the Spode factory created for the White Star Line of luxury liners, including the Titanic. The Spode porcelain factory is still in operation today.
Distinguishing between ceramics and pottery is challenging. Definitions overlap and are not universally agreed upon. Most resources list pottery as a type of ceramic while a few try to separate them with characteristics that, frankly, confuse me. For the purposes of this article, I shall stick with the standard.
As I decipher it, a ceramic can be created from a number of base materials (including and typically clay), whereas pottery must be made from clay. Breaking it further, pottery as a category encompasses earthenware, stoneware, and porcelain. The major factor in classifying pottery is in the temperature used when firing. As a rough guide, earthenware is normally fired at temperatures in the 1,830°F to 2,190°F range, stoneware at between 2,010°F to 2,370°F, and porcelain at 2,190°F to 2,550°F. Porcelain, since the base is kaolin clay, is technically a type of pottery, but its unique qualities set it apart in the overall world of ceramics.
Earthenware is glazed or unglazed, opaque and non-vitreous, and is capable of being scratched with a knife. Unless glazed, earthenware is not watertight. Terracotta is the most common type of earthenware. Historically, reaching high temperatures for the length of time to complete the drying process was difficult. What this means is that earthenware (which can be fired effectively as low as 1,050°F) was achievable in primitive pit firing, is the earliest form of pottery, and the most plentiful ancient pottery shards and pieces uncovered archaeologically.
Stoneware is the broad term for pottery fired at a higher temperature. The result is dense, impermeable, more opaque, normally glazed, and hard enough to resist scratching. It is usually colored grey or brownish because of impurities in the clay used for its manufacture. Historically, across the world, stoneware has usually been developed after earthenware (but before porcelain) as kiln technology advanced, and has been used for high-quality as well as utilitarian wares.