Did you know that Chinese ceramics were once considered high-tech? For many years, China was the only civilization that knew how to make porcelain. Through years of research and experimentation, the Chinese developed secret techniques that no one else knew about. People from all over the world wanted these wonderful treasures, and the Chinese were very eager to sell them.
How Are Ceramics Made?
Ceramics are generally made from three basic elements:
Clay + Glaze + Heat
They are formed into shapes by hand, using molds, or by turning on a potter’s wheel.
Clay is basically rock that has been ground down over thousands of years. It is different from sand or ordinary mud because it holds its shape and keeps shape when it is heated (or fired) in a kiln. Kilns are ovens that are specially made for firing ceramics.
Clay, although common, is not found everywhere, and ceramics industries often grow where this key raw material is available. Because heat is also needed there is another crucial raw material: fuel for firing the kiln.
After cleaning and preparing the clay, potters mix it with water to make it easier to handle. Clay vessels (pots, dishes, vases, and other containers) and sculptures are formed in several ways:
- building by hand (pinching, coiling, and slab building)
- shaping on a potter’s wheel
- forming in molds
Chinese tomb sculptures were formed in molds and then painted or glazed. The other ceramics were formed on potter’s wheels. A lump of clay is thrown on a turning wheel and shaped with the hands as the wheel turns.
The clay used to make fine porcelain china is called kaolin, from the Gaoling Mountains of southeastern China, where it was first mined. Chinese potters mixed the kaolin clay with a powder ground from a stone called baidunzi, a rock that contains feldspar, a glassy mineral. In the very hot kilns, the stone melts and makes the clay hard and shiny like glass.
Glaze acts as the skin of the pot, making it waterproof and providing decoration. It often feels like glass when you touch it.
Glaze is made up of four main ingredients:
- clay, often the same clay as the object,
- glassy minerals, often silica found in sand, that melt to make the body hard,
- a flux, a mineral such as feldspar or calcium that allows the glaze to melt at a lower temperature, and
- minerals to add color such as cobalt (blue) or manganese (purple).
The potter mixes the glaze ingredients with water and then applies them to the vessel or sculpture, sometimes with a brush or by spraying, pouring, or dipping the object into the glaze.
There are many different glaze recipes, and Chinese potters sometimes kept their formulas very secret.
To become usable ceramics, clay objects have to be fired in kilns, in the same way that bread dough is baked in an oven to become bread.
The water must be removed from the wet clay and the clay particles must melt together for the pot to harden and keep its shape. Over the centuries, pots have been fired in kilns varying from simple bonfires to long kilns that climb up the side of hills.
Kilns usually have three main sections:
- a firebox (containing the fuel),
- a firing chamber (containing the pots ), and
- a chimney.
Heat moves from the firebox through the firing chamber and up through the chimney. Traditional Chinese potters used wood and coal as fuel, but today electric kilns are increasingly popular.
Different clays require different firing temperatures and firing times-a clay vessel that has not dried completely before firing can sometimes explode! The colors of the glazes can vary according to the amount of oxygen in the kiln during firing. So, the potter watches the kiln very carefully during firing. After firing, the pots are left to cool before they are taken out.