Clay Terminology

Plasticity –

Plasticity is a property exhibited by soft clay. Force Exerted effects a change in shape and the clay exhibits no tendency to return to the old shape. Elasticity is the opposite.

Temper – 

Temper is a non-plastic material added to clay to prevent shrinkage and cracking during drying and firing of vessels made from clay. 

Sintering – 

Sintering is the process of forming a solid mass of material through heat and pressure without melting to the point of liquification. This process involves the atoms in materials diffusing across the particle boundaries and fusing together into one piece. 
 

Vitrification – 

Vitrification is the progressive partial fusion of a clay, or of a body, as a result of a firing. Essentially vitrification is how non-porous or glass like a piece becomes in firing. A fully vitrified piece will hold water without a glaze. 
 

Candling – 

Candling is the process of firing clay very slowly in the first stage of firing. This is done below the temperature of waters boiling point, 212 degrees fahrenheit. Candling is done to prevent cracking, breaking and explosions. 
 

Oxidation – 

Oxidation occurs when there is an excess of oxygen. As the kiln heats up, compounds in the glaze break off and oxygen attaches itself to the glaze and clay. The thermal heating causes minerals in both the glaze and clay body to oxidize, giving a wide range of effects. 

Reduction – 

Reduction occurs when there is a deficit of oxygen. This deficit creates gases in the kiln, which leach oxygen out of the glaze and clay minerals.

Wedging – 

A process by which the clay is compacted, removing any air trapped in the clay body.

Vessel – 

A hard brittle material made by firing clay and similar substances.

Burnish – 

To polish something by rubbing. In terms of ceramics, it is to polish the clay body by compacting the clay particles.

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