Clay is fine particles that form from weathered rocks and minerals. Ancient cultures discovered clay could be shaped and used to make pottery as early as 8,000 BCE in the Middle East. There are two main types of clay - primary kaolin clay found where it was originally formed, and secondary clay that has eroded and been carried elsewhere. To prepare clay, it is wedged to remove air, allowed to dry to the leather-hard stage, and then fired first in a bisque firing and finally glazed and fired again to produce finished pottery. Modern kilns use gas or electricity to fire clay to the appropriate temperature indicated by pyrometric cones on a cone chart.

1. CLA
Y!

2. What is it?
Fine particles of
dirt which float in
a stream or river
then sink to the
bottom- breaks off
from rocks
River valleys tend
to have a lot of
clay.

3. Ancient Cultures
Ancient man discovered that
clay could be shaped and
modeled into forms both
 decorative and functional.
Some of the earliest pottery
has been found in the Middle
East and dates to
 between 8,000-7,000 BCE.
Japanese ceramics have
flourished since over 4,000
years ago
Native American pottery
shards have been found dating
back over 3,000 years.

4. Types of Clay
PRIMARY: (Kaolins)
– Has been in the same
place for millions of
years.
– Not good for
building.
– Always WHITE in
color.

5. Kaolin (primary) clay
Not used as much in
ceramics, except for
porcelain
But, is used in paper
making, toothpaste,
cosmetics, and paint!

6. Types of Clay
SECONDARY:
– “Art” clay- can be
worked and shaped
– Variety of colors: reds,
yellows, whites, blacks,
greys
– Carried into riverbeds-goes
to a ‘secondary’
place from the original
rock and contains more
impurities/smaller
particles

7. Secondary Clay

8. US Clay “Map”

9. Preparing Clay for Use
Wedging- process of
removing air from the
clay.
– Necessary to remove air
from the clay in order to
keep it from exploding in
the kiln
– Wedging is done by
kneaded or ‘throwing’ the
clay down in the
appropriate wedging area.

10. Preparing Clay for Use
Dry Time
– Unless clay is kept wet with a squirt
bottle it will dry out. IT MUST BE
COVERED when you are still working
on it.
– Cracks will start to appear and the clay
will be difficult to work with.

11. Preparing Clay for Use
Slip and Score
– When joining 2 pieces of clay together
it is necessary to do the “3 S’s”: SLIP
and SCORE, SMOOTH each piece.
– Slip is like glue for clay
– Scoring helps the pieces fit together
like puzzle pieces
– Smoothing makes the pieces
STRONGER and look like seamless

12. Preparing Clay for Use
Slip and Score

13. Preparing Clay for Use
Hollowing Out
– In order to prevent
breakage and explosions
in the kiln, clay must be
HOLLOWED OUT if it
is over ½ inch thick.
– Hollowing out also
allows the clay to dry
faster.

14. Preparing Clay for Use
 Hollowing Out
– Newspaper can be used
to hold the shape of
the project once it is
hollowed out.
– YOU MUST POKE
HOLES where you’ve
hollowed out,
otherwise you’ve
created a giant air
bubble and it will
explode!

15. Stages of Clay
Leather-hard
The condition of a clay body
when much of the moisture
has evaporated and
shrinkage has just ended,
but the clay is not totally
dry. Carving, burnishing, or
joining slabs are often done
at this stage.
Bone Dry
Clay that has the moisture
completely evaporated. It
can no longer be scored and
slipped withouta
compromising the strength
of the piece.
Greenware
Unfired pottery or sculpture.
Bisque
Clay that has been fired to a
state hard enough for
glazing

16. Firing
Clay must be left
in the open air to
dry
(GREENWARE)
before it can be
FIRED in the
kiln.
(BISQUEWARE)

17. Greenware
Clay is ‘leather
hard’
Most of water
has evaporated
Most fragile
state
Has not been
fired yet

18. Bisqueware
Clay that has undergone
one firing
Clay is now
CHEMICALLY
ALTERED. Cannot be
worked anymore/be
turned back into slip or
clay.
Sturdier than greenware

19. Glazeware
Bisqueware that
goes through a
second firing,
with glaze applied
“Final” firing

20. Kilns
 Ovens used to fire
clay
1. Pit kilns-
(prehistoric)-
simplest. Shallow
pit dug in the
ground. Made
pots very fragile
and porous.

21. Kilns
2. Beehive Kilns- greater
heat, pots are stacked
in a chamber with fire
burning from
underneath.
3. Natural Gas Kilns-more
modern. Similar
to Beehive kiln except
natural gas is used
instead of firewood.

22. Kilns
4. Electric Kilns- 20th century. Heated
by an electric current that heats coils
throughout.
- Pyrometric Cones- pyramids made of
ceramic materials that tell the actual
temperature of the kiln during firing.
Used to check to accuracy of the firing

23. Cone chart
 Named after the pyrometric
cones, to tell how hot the kiln
was before we could accurately
measure the temperature
 Generally refers to certain
temperatures. Clays all have a
firing ‘cone’ as well as glazes.
(Make sure they match up!)
 The clay you are using is cone
04 to cone 06. This means it
fires at about 1,855-1,971
degrees F

24. Clay Disasters

25. Kiln Firing Video