What is Clay?

Clay is a mixture of decomposed igneous rock and organic matter that becomes hardened when fired.

Clay is created when rocks containing feldspar break down through weathering and erosion over time. This breakdown releases microscopic particles of clay minerals, often kaolinite, along with other minerals like iron and calcium.

Clay is composed of fine particles of clay minerals, which are essentially hydrous aluminum silicates. The specific composition can vary depending on the source rock and the weathering processes involved.

The Stages of Clay

Slip (Wet) - watered down clay used as pottery glue
Plastic (Greenware) - Clay that you can easily mold
Leather Hard (Greenware) - Clay that is a little dry. Good for Carving
Bone Dry (Greenware) - Clay that is completely dry and ready for firing
Biqueware (First Firing) - Clay that has been fired once. Solidified
Glazeware (Second Firing) - Clay that has been fired with glaze

The 3 Properties of Clay

Plasticity

Plasticity in clay refers to its ability to be molded and shaped without cracking or losing its form.

Shrinkage

Clay shrinkage refers to the reduction in size that occurs when clay dries and is fired.

This happens because of water loss and physical/chemical changes during the drying and firing processes.

The amount of shrinkage varies depending on the type of clay and the firing temperature.

Porosity/Permeability

Porosity is concentration of the spaces between particles of a material.

Clay has a high porosity, meaning it contains a large amount of pore space within its structure. This high porosity is due to the small, plate-like particles that make up clay, which don't pack tightly together, leaving many interconnected spaces.

However, while clay has high porosity, it also has low permeability, meaning water and other fluids do not flow through it easily due to the small size and tortuous paths of the pore spaces.

Page updated

Report abuse