Not Your Ordinary Mud What is Ceramics Objects made from any type of clay that is fired with the aid of heat Historical Ceramic Origins Dates back to when mankind first learned to control fire ID: 239887
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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 PotsSlide34Slide35
http://
www.youtube.com/watch?v=SA-rGYh2UH0Slide36
Slab Built
http://www.youtube.com/watch?v=Dn55cIO8D2ESlide37Slide38Slide39Slide40Slide41
Tools
Rib
Loop
Wire
Fettling Knife
Wood Modeling Tool
Needle