Intro to Clay: Composition, Stages, Tools, and Techniques

Clay

Moist earth made of decomposed rock.

What is Clay?

A soft, earthy material made of minerals created through erosion of the earth's crust over time.

Clay Composition

Primarily alumina, silica, and water; may also contain iron, potassium, sodium, and calcium.

How Clay is Formed

Mechanical and chemical weathering over millions of years breaks rock into tiny particles (platelets).

Mechanical Weathering

Physical processes like freezing/thawing, glaciers, rain, streams, and tree roots breaking down rock.

Chemical Weathering

Acidic reactions with decomposed organic matter that break down rock.

Firing

Baking clay at a high temperature.

Kiln

An oven used for firing clay.

Plastic (Plastic Clay)

Wet, workable clay that can be shaped.

Plasticity

The ability of clay to hold together while being shaped (workability).

Leatherhard

firm but not fully dry; good for carving.

Greenware

Clay that is dry but has not been fired.

Bone Dry

Clay with no moisture left; ready for the first firing.

Bisqueware

Clay that has been fired once.

Glazeware

Clay that has been glazed and fired a second time.

Slip

A mixture of clay and water used for joining pieces or decoration.

Scoring

Roughing up clay surfaces to help pieces stick together.

Score and Slip

Technique using scoring and slip to create a strong bond between clay pieces.

Knead / Wedge

Used to remove air bubbles and prepare clay for working.

Slip / Slurry (Stage 1)

Clay mixed with water to a pudding-like consistency.

Plastic (Stage 2)

Soft, workable clay that can be shaped and formed.

Leather Hard (Stage 3)

Partially dried clay; ideal for carving and attaching pieces.

Bone Dry (Stage 4)

Completely dry clay; very fragile; ready to be fired.

Bisqueware (Stage 5)

Clay that has been fired once and cannot return to clay.

Glazeware (Stage 6)

Clay that has been glazed and fired a second time.

Clay Can Be Recycled Until

The greenware stage.

Recyclable Stages of Clay

Slip, wet clay, leather hard, greenware, bone dry.

Earthenware

Low-fire clay; often red or white; porous after firing.

Stoneware

Mid- to high-fire clay; strong and durable; good for functional pottery.

Porcelain

High-fire clay; very fine-grained; white and sometimes translucent.

E.S.P.

Earthenware, Stoneware, Porcelain.

Ceramics

Objects made from clay and hardened by firing.

Pottery

Containers made from clay by hand or wheel.

Difference Between Clay, Ceramics, and Pottery

Clay is the material, ceramics are fired objects, pottery is ceramic containers.

Pinch Method

Using fingers to pinch and shape clay.

Needle Tool

Used for cutting, detailing, and popping air bubbles.

Wire Cutter

Used to cut clay from a block or wheel.

Loop Tool

Used for carving and removing clay.

Ribbon Tool

Used for trimming.

Wood Modeling Tool

Used for smoothing clay.

Wooden Rib

Used to shape the surface.

Metal Rib / Scraper

Used to scrape clay.

Sponge

Used to add or remove water and smooth surfaces.

Paddle

Used to pat the clay down.

Scoring rib

Scores the clay.

Clay Shrinkage

Clay shrinks during drying and firing, usually 5-10%.

Why Clay Shrinks

Water leaves the clay and particles move closer together.

How to Prevent Cracks from Shrinkage

Dry clay slowly and evenly.