Lynn Kallberg, age 14, of Duluth, Minn., for her question:
WHAT EXACTLY IS BONE CHINA?
Bone china is a special kind of fine porcelain chinaware. It is very hard and durable, glossy bright and almost as white as pure snow. It was invented by the potters of England some two centuries ago. And, if you suspect that it is made from old bones, you are at least partly correct.
The first pottery was made from molded clay, either dried in the sun or roasted in the ashes of a campfire. It was invented before the dawn of history, perhaps by accident. Nowadays, pottery of this type is called earthenware and one might never suspect that it is related to the lovely chinaware we call porcelain. Actually, the only difference is in the earthy ingredients and the baking or firing process.
Porcelain originated long ago in China and the Chinese refused to reveal their secret recipes. So the potters of Europe tried to invent their own. Their experiments resulted in three main types of very fine porcelains called hard paste, soft paste and bone china.
The paste refers to the muddy mixture of clay type ingredients, including kaolin and petuntse, or china stone. The fine particles in kaolin are decomposed feldspar and granite type rocks. Petuntse contains glassy silicate, feldspar, alumina, potash and perhaps a trace of soda. In the baking kiln, the kaolin particles are embedded in a glassy goo of fused kaolin.
Hard paste porcelain is very white and quite opaque. The ingredients in soft paste porcelain may be fusible silicate and white firing clay. It is less white and somewhat more translucent than the hard paste, though both are very fine porcelains.
Bone china, invented by English potters, is closer to the true porcelains of China. Ashes of burned animal bones are added to the powdered mixture of kaolin and petuntse. The bone ash provides calcium phosphate and adds the good qualities of both hard and soft paste. This recipe is easier to handle and less expensive to make than the hard and soft paste types.
Some claim that the bone china recipe was invented by Josiah Spode in 1800. Some suspect that others stumbled upon the secret somewhat sooner. In any case, this lovely porcelain was invented in England and the potteries of England still produce most of the world's supply.