Transcript Clay - Images

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 Rock
Weathering
Primary Clays
Secondary Clays
Porcelain Clay
Stoneware Clay
Earthenware 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.
2.
3.
4.
5.
6.
Freezing and thawing
Grinding of glaciers
Pounding of rain
Flow of rushing streams
Probing of tree roots
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. 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
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
Earthenware
Stoneware
REMEMBER: E.S.P.
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.
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. 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 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.
… identify and list the various processes for
transforming clay into ceramic forms.
… identify and categorize the physical
characteristics of each stage of clay.
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
Materials: Stages of Clay worksheet
Various examples of clay at different
stages
Directions: Fill out the Stages of Clay worksheet
by Studying the physical characteristics of
each stage of clay.