Introduction to Clay - PowerPoint Presentation

Slide1

Introduction to Clay

Not Your Ordinary “Mud”Slide2

What is Ceramics?

Objects made from any type of clay that is fired with the aid of heatSlide3

Historical Ceramic Origins

Dates back to when mankind first learned to control fire

Anthropologists use Stone Age clues to piece together a variety of possible theories.Slide4

What is Clay?

Clay is . . .

. . .a fine mixture of decomposed igneous rock minerals and organic matter Slide5

2 Types of Clay Deposits

Primary

Clays

Secondary

ClaysSlide6

Primary Clays

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

Fewer impurities

Coarser grained texture (less weathered)

Highly refractory (resistant to heat/high fire)

Low plasticity (harder to work with)

Whiter fired color (Porcelain)Slide7

Primary Clay Example: Porcelain

Bright white clay – very pure

Translucent (light passes through)

High Fire – matures at 2419 degrees F.

A very hard clay

Vitrifies = non-porous

Smooth – very fine, not as plastic

Feels very dry (harder to throw)

Still white when bisqueSlide8

Secondary Clays

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

Finely ground (more weathered)

Contaminated with

organic

matter

More plastic

Stoneware & EarthenwareSlide9

Secondary Clay Example: Stoneware

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 safeSlide10

Secondary Clay Example: Earthenware

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 vitrifySlide11

Identify the Clay Body Type

(How do you know?)

REMEMBER: E.S.P.

E

arthenware

S

toneware

P

orcelainSlide12

Part 2: Clay PropertiesSlide13

Clay Terms to Know

PlasticityShrinkagePorosity

Aging

Wedging

VitrificationSlide14

3 Major Properties

Plasticity

Shrinkage

Porosity

These 3 properties must be considered before choosing a clay body.Slide15

Plasticity is. . .

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 CoilSlide16

How do you improve clay’s plasticity ?

AGING,

WEDGING,

&

ADDING MOISTURESlide17

What is aging?

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.Slide18

How does wedging help?

Aligns clay particles

Equalizes moisture

Removes air bubbles

Makes clay texture uniform

Tip:

You should always wedge first before using your clay.Slide19

How do I add moisture?

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.Slide20

Shrinkage is. . .

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.Slide21

What happens if shrinkage occurs unevenly?

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

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

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.Slide22

Result Example

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.Slide23

Porosity is…

The capacity of a clay body to absorb moisture

Based on the amount of space in the structure of the fired clay bodySlide24

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.Slide25

Clay Terms to Know

KilnConeSlurryWet

Leatherhard

Greenware

Bisqueware

GlazewareSlide26

Mixing & Recycling Clay

Clay may be recycled up through greenware stage.Slide27

Firing: The Electric Kiln

The Kiln is a chamber to heat clay

It creates chemical changes to the clay and glazes which create greater strength and permanencySlide28

The Firing Cycle

8-12 hours to heat

+ 8-12 hours to cool

16-24 hours for firing cycle

Slide29

Firing Temperatures

Porcelain

White Hot Heat

2400 degrees F.

Stoneware

2200 degrees F

Earthenware or

Bisqueware

Red Hot Heat

1800 degrees F.Slide30

Important Tip!

After the clay has been fired it

CANNOT

be recycled!Slide31

Stages of Clay

1. Slurry (potter’s glue): Liquid clay

2.

Wet/Soft:

Plastic clay

3. 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 porosity

6.

Glazeware:

fired more than once, vitreousSlide32

Pinch Pots

http://www.youtube.com/watch?v=r1IT68soL-kSlide33

Coil PotsSlide34
Slide35

http://

www.youtube.com/watch?v=SA-rGYh2UH0Slide36

Slab Built

http://www.youtube.com/watch?v=Dn55cIO8D2ESlide37
Slide38
Slide39
Slide40
Slide41

Tools

Rib

Loop

Wire

Fettling Knife

Wood Modeling Tool

Needle