Continuing with the subject of porcelain, in my previous blog I introduced how porcelain was first produced in Japan via the Koreans. To go to the original source of porcelain involves travelling back through Korea to China a few centuries earlier. The site is Mount Gaoling close to the town of Jingdezhen in Jiangxi province, China. From first encounters with the incredible Song, Yuan and Ming Dynasty porcelain from China that entered Europe via trade routes to Africa and the Middle East, Europeans for a long time strived to discover the secret of this mysterious white clay. It wasn’t until 7 Centuries after the Chinese started producing porcelain that the Europeans discovered the secret to making porcelain in the 18th Century.
The secret lay in one of the core ingredients, kaolin (Al2O2 2SiO2 2H2O). Kaolin is what gives porcelain its whiteness, because it is a primary clay and generally over 95% free of impurities. The word ‘kaolin’ is derived from the mountain village ‘Gaoling‘ (‘high ridge’), which rests 553m above sea level just outside Jingdezhen. It was in these mountains that kaolin was discovered and from which the first porcelain was produced. Below are images of the kaolin dusted paths through the forest and the old mining tunnels.Kaolin is an example of a residual clay mined directly from its source. Having hardly been subjected to erosion and weathering and pushed along the landscape like secondary clays, kaolin generally remains in larger particles and is therefore not as plastic as other clays. The leaching out of alkalis and impurities leaves a pure white firing clay that can be taken to high temperatures. Porcelain is also special because of its ability to vitrify to translucency without collapsing.
In Europe, ‘China clay’ is the name frequently adopted for kaolin. Porcelain clay is composed of mixtures of quartz, kaolin/China clay, feldspar and ball clay (ingredients can vary slightly). Each ingredient has a its own special effect on the way the porcelain matures in the kiln and performs.
The kaolin mined in Gaoling was crushed to finer particles using water powered trip hammers which are still running at the site today.
I will add more to this at a later date.