Not Your Ordinary “Mud”

… define clay.… describe the natural process that form clay.… identify primary and secondary clays.… Identify porcelain, stoneware, and

earthenware as being primary or secondary clays.

Clay Igneous RockWeatheringPrimary ClaysSecondary ClaysPorcelain ClayStoneware ClayEarthenware Clay

Clay is . . .. . .a fine mixture of decomposed igneous rock minerals and organic matter

Igneous Rock

1. Melted rock is cooled and solidified into igneous rock (mother rock) which makes up earth’s crust.

2. Mechanical weathering over millions of years breaks down the rock from boulders into stones, to pebbles to fine, small particles known as platelets.

Weathering

1. Freezing and thawing2. Grinding of glaciers3. Pounding of rain4. Flow of rushing streams5. Probing of tree roots6. Acidic reactions with decomposed organic

matter (chemical weathering)

. . .aids in moving particles away from the site of origin resulting in 2 types of clay deposits.

1.1. Primary Primary ClaysClays2.2. SecondarySecondary Clays Clays

Clays which remain at the site (mother rock) where they were formed.

Fewer impuritiesCoarser grained texture (less weathered)Highly refractory (resistant to heat/high fire)Low plasticity (harder to work with)Whiter fired color (Porcelain)

Bright white clay – very pureTranslucent (light passes through)High Fire – matures at 2419 degrees F.A very hard clayVitrifies = non-porousSmooth – very fine, not as plasticFeels very dry (harder to throw)Still white when bisque

Clays which have been transported by wind, glacier, water, etc. away from site of origin

Finely ground (more weathered)Contaminated with organic matterMore plastic Stoneware & Earthenware

Gray to tan or brown when moist Non-translucent Matures at 2232-2381 degrees F. Vitrifies = non-porous Pinkish color when bisque Very durable = dinnerware safe Used by Burke Pottery

Reddish brown clay that matures at a low temperature (approximately 1830 degrees, which is red hot heat.)

Also known as terra cotta (baked earth) Flower pot clay Remains porous Does not vitrify

REMEMBER: E.S.P.

Earthenware Stoneware Porcelain

In your sketchbook, choose one of the discussed topics, about which you’d like to write a paragraph.

Use your own words and be descriptive. Try not to re-write the definitions found here.

3-5 Sentences.

When hot magma from under the earth’s crust cools, it becomes a solid called “igneous rock.” Over millions of years, through a process known as “mechanical weathering,” this igneous rock is broken down from boulders to rocks, rocks to pebbles, and finally pebbles to small particles called platelets. These platelets are mixed with organic matter and clay is formed.

… identify the characteristics of the three major properties of clay: Plasticity, Shrinkage, and Porosity

… Perform test to determine a clay body’s plasticity, shrinkage, and porosity.

PlasticityShrinkagePorosityAgingWedgingVitrification

1. Plasticity2. Shrinkage3. Porosity

These 3 properties must be considered before choosing a clay body.

The ability to hold together while being shaped (workability)

Does it stretch and bend without breaking?

Test It! Wrap a coil around your finger. If it cracks, the clay is not plastic.

Plastic

Not Plastic

Create the Coil

AGING,WEDGING,

&ADDING MOISTURE

Storing well mixed clay for 3 plus weeks which causes a chemical breakdown of the organic matter contained in the clay.

Older is better!

Historical Fact: The Chinese aged clay for whole generations.

1. Aligns clay particles2. Equalizes moisture3. Removes air bubbles4. Makes clay texture uniform

Tip: You should always wedge first before using your clay.

All clay contains water.Clay dehydrates when exposed to air.Add water to clay to make it more plastic.Too little or too much water causes clay to

become less plastic.

Tip: Mist clay with water bottle or dampen it with a wet sponge. Always wrap your projects with plastic before storing.

Contraction of clay (or glaze) during both drying and firing processes.

Clay shrinks 12-15% Shrinkage depends on the clay body’s

composition.Tip: It is important to understand the shrinkage

of your clay body since it has a tendency of cracking and warping during this process.

1. Water between clay particles moves to the surface and evaporates

2. Clay particles move closer together until touching.

3. Shrinkage stops and remaining water between pores evaporates.

Tip: Drying should occur more slowly during stages A and B as seen in the diagram

1. When a drying tile rests on a smooth surface, the upper face will dry first.

2. The tile will curl up because the upper face is smaller than the lower face (uneven shrinkage).

3. Later when the tile is completely dry the curl remains as the body is too rigid to completely straighten out.

Tip: In addition to warping, uneven shrinkage may also cause cracking. These defects may be prevented with slow overall drying or delay the drying of certain parts by covering.

1. Make a cylinder 5” tall and 5” in diameter with ½” thick walls for each clay body.

2. Place the cylinder on a piece of paper, tracing around the base.

3. Measure and record the exact diameter, height, and thickness of the wall.

4. Re-measure the form after firing. Subtract the difference and divide by the original wet measurements to get the percentage of shrinkage.

Optional: Make a 2” x 11”x 1/2” slab. Score a 10” line down the middle. Measure and divide the difference by 10 to get the shrinkage rate.

If the shrinkage rate is 10%, then the final glaze-fired piece of any object made from that clay body will only be 90% of the original wet clay size.

The capacity of a clay body to absorb moisture Based on the amount of space in the structure of the

fired clay body

High Porosity allows more water into or through clay body.

Keep it inside during the winter and use a trivet to protect your coffee table!

Low Porosity, or vitrified clay, allows little or no water into or through the clay body.

Vitrification: When a clay is fired to its maturing temperature it loses its porosity and transforms into a hard, nonabsorbent, glasslike state.

… identify and list the various processes for transforming clay into ceramic forms.

… identify and categorize the physical characteristics of each stage of clay.

KilnConeSlurryWetLeatherhardGreenwareBisquewareGlazeware

Clay may be recycled up through greenware stage.

The Kiln is a chamber to heat clay It creates chemical changes to the clay and glazes

which create greater strength and permanency

8-12 hours to heat

+ 8-12 hours to cool 16-24 hours for firing cycle

PorcelainWhite Hot Heat2400 degrees F.

Stoneware2200 degrees F

Earthenware or BisquewareRed Hot Heat1800 degrees F.

After the clay has been fired it CANNOT be recycled!

1. Slurry (potter’s glue): Liquid clay2. Wet/Soft: Plastic clay3. Leatherhard: not easily distorted, maintains

form and can be smoothed, carved, and added to

4. Greenware (bone-dry): Water is evaporated; form is brittle

5. Bisqueware: once-fired, maintains porosity6. Glazeware: fired more than once, vitreous

Materials: Stages of Clay worksheetVarious examples of clay at different stages

Directions: Fill out the Stages of Clay worksheet by Studying the physical characteristics of each stage of clay.