The Chemistry of Pottery

pottery

Pottery is one of the oldest arts of humankind. It is the process of shaping clay into vessels and vases that are both functional and artistic. It is a fascinating craft and the history of pottery has fascinated scholars and historians for over 18,000 years. But how does clay extracted from the earth become a colourful pot? And what’s the chemistry behind it all?

The first requirement for making pottery is that there must be usable clay available. Archaeological sites that have produced pottery typically have been near large deposits of clay. The second requirement is that the clay must be able to be heated to transform it into ceramic. Methods for creating fires hot enough to do this did not develop until later in the development of cultures.

Once the clay is shaped, it must be dried completely before firing. This is achieved by a process known as kneading, which involves massaging the clay to allow moisture to spread throughout the slab. Then the item must be dried to a stage called leather-hard, which means that it is firm but still pliable and can be trimmed, sculpted or carved. It must also be fired to a stage called bone-dry, which is when the clay body has a moisture content that is close to zero.

Once the clay has been dried and fired, it can be glazed using either a liquid or a powdered mixture of glass solids and water. Depending on the type of glaze used, it can be coloured in a variety of ways. The most common colourants are oxides of copper, which give the blue or green appearance that is so characteristic of pottery.

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