Not Your Ordinary “Mud”
Objects made from any
type of clay that is fired
with the aid of heat
Dates back to when mankind first learned to
control fire
Anthropologists use Stone Age clues to piece
together a variety of possible theories.
1. Primary Clays
2. Secondary 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)
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 bisque
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 & Earthenware
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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
 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
Earthenware
Stoneware
REMEMBER: E.S.P.
Porcelain
Plasticity
Shrinkage
Porosity
Aging
Wedging
Vitrification
1. Plasticity
2. Shrinkage
3. Porosity
These 3 properties must be considered before
choosing a clay body.
 The ability to hold
together while being
shaped (workability)
Create the Coil
 Does it stretch and bend
without breaking?
Plastic
 Test It! Wrap a coil
around your finger. If it
cracks, the clay is not
plastic.
Not Plastic
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.
2.
3.
4.
Aligns clay particles
Equalizes moisture
Removes air bubbles
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. 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.
If the shrinkage rate is 10%, then the final glazefired 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.
Kiln
Cone
Slurry
Wet
Leatherhard
Greenware
Bisqueware
Glazeware
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
Porcelain
White Hot Heat
2400 degrees F.
Stoneware
2200 degrees F
Earthenware or
Bisqueware
Red Hot Heat
1800 degrees F.
After the clay has been fired it
CANNOT be recycled!
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, vitreous
Pinch Pots
http://www.youtube.com/watch?v=r1IT68soL-k
Coil Pots
http://www.youtube.com/watch?v=SA-rGYh2UH0
Slab Built
http://www.youtube.com/watch?v=Dn55cIO8D2E
Rib
Fettling Knife
Loop
Wood Modeling Tool
Wire
Needle