Clay Bodies

What is clay

Clay is an inorganic compound derived from decomposed rocks

What is clay chemically composed of

Alumina, Silica, and Water

What gives clay its plasticity

The alumina and silica create platelets that are bound together by water allowing them to move and be plastic

What are the two categories of clays

Primary and secondary

What are primary clays

Clay that is found where it is formed

What are secondary clays

Clays that have moved from the formation site resulting in various degrees of contamination

Examples of primary clays

Kaolin and bentonite

Examples of secondary clays

Ball Clay, Stoneware, Earthenware, Some Kaolin

Characteristics of Kaolin clay

Purest form of clay, large consistent particle size, non-plastic, fires white, very resistant to high heat

Characteristics of ball clay

Contains some contaminates, small particle size, most plastic type of clay, fire to off-white color, resistant to high heat, high shrinkage rate, high green strength

Characteristics of fire clay

Contains more contaminates, mixture of particle sizes, very course, high green strength, high heat resistance, fires off-white to brown

Characteristics of stoneware

Similar to fire clays, mixed particle sizes, mildly plastic, high green strength, high heat resistance, low shrink rate, can be worked without any additions

Characteristics of earthenware

Highest amount of contaminates, fine particles, somewhat plastic, fires to a red color, flux at high temps

What is a clay body

The combination of different kinds of clay

Qualities to consider when making a clay body

Color, plasticity, firing temp, vitrification, texture, glaze fit, cost

What is the most common glass former

silica

What does a glass former do in a clay body when fired

Molten Glass fills voids between clay particles resulting in watertight body (vitrifies)

What is the importance of fluxes in a clay body

determines what temperature that the clay body matures at

High fire fluxes

Custer Feldspar, Soda Feldspar, Nepheline Syenite, Cornwall Stone

Mid fire fluxes

Nepheline Syenite, Frit

Low fire fluxes

Frit

What is temper

added to help the clay survive the firing process (fast fire bodies will experience stress and this helps alleviate that)

Common tempers

Grog (crushed fired clay), sand, talc

What is filler

added to give green strength to a clay body (can result in lower fire strength)

Common Fillers

Sand, grog, paper pulp, nylon, feldspar chunks