Clay: Formation, Types, Properties, and Applications

Geological Processes and Clay Formation

Clay is formed through two geological processes: weathering and erosion.

Source Material for Clay

The material broken down into clay by these processes is primarily granite rock.

Classifications of Clay

Clay is classified into two categories based on its location:

• Primary clay: Found at the source of its formation, it is considered"pure" and includes only kaolin.
• Secondary clay: Found far from its source, it has traveled through erosion, picking up contaminants and undergoing particle size changes.

Types of Clay

There are six unique types of clay:

• Kaolin: Pure, white, low plasticity, used in porcelain production.
• Fire clay: Coarse, contains metallic oxides, fires to various colors, highly refractory, used in industrial applications.
• Ball clay: Highly plastic, dark grey when raw, fires white.
• Stoneware: Combines the plasticity of ball clay with the strength of fire clay, durable, wide firing range.
• Bentonite: Formed from volcanic ash, extremely fine particle size, highly plastic, used in small amounts to enhance plasticity.
• Earthenware: Fires at low temperatures, typically orange-toned, but can vary in raw color.

Clay vs. Clay Body

A clay is a specific type of clay material extracted from the ground. A clay body is a mixture of different clays and sometimes non-clay materials, making it easier to work with.

Plasticity

Plasticity refers to the ability of clay to bend and form without breaking or cracking.

Testing Plasticity

The"pencil test" is used to check plasticity: roll a clay coil to the width of a pencil and try to wrap it around your finger. If it wraps without cracking, the clay is considered relatively plastic.

Wetness Stages of Clay

Clay goes through four wetness stages:

• Slip: Liquidy, sticky.
• Plastic clay: Moldable, wet but not sticky.
• Leatherhard: Firm, carvable.
• Bone dry: Dusty, pale in color.

Ceramic Work Stages

After creation, ceramic work undergoes four stages:

• Greenware: Unfired clay (leatherhard or bone dry).
• Bisque ware: Fired once.
• Glaze fired: Fired again after glazing, enhancing durability.
• Additional firings: Optional, for adding surface decorations.

Applications of Ceramics

Beyond art, ceramics have various applications:

• Medicine: Hip joints, braces.
• Electronics: Cell phones, spark plugs.
• Military: Bulletproof vests, cockpits.
• Space: Space shuttle tiles.

Refractory

Refractory refers to materials that are highly durable, heat-resistant, and withstand thermal shock well.