CLAY!

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.

Ancient CulturesAncient 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 agoNative American pottery shards have been found dating back over 3,000 years.

Types of ClayPRIMARY:

(Kaolins)– Has been in the

same place for millions of years.

– Not good for building.

– Always WHITE in color.

Kaolin (primary) clay

Not used as much in ceramics, except for porcelain

But, is used in paper making, toothpaste, cosmetics, and paint!

Types of ClaySECONDARY:

– “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

Secondary Clay

US Clay “Map”

Preparing Clay for UseWedging- 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.

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.

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

Preparing Clay for UseSlip and Score

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.

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!

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 DryClay that has the moisture completely evaporated. It can no longer be scored and slipped withouta compromising the strength of the piece.

BisqueClay that has been fired to a state hard enough for glazing

Greenware Unfired pottery or sculpture.

Firing

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

Greenware

Clay is ‘leather hard’

Most of water has evaporated

Most fragile state

Has not been fired yet

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

Glazeware

Bisqueware that goes through a second firing, with glaze applied

“Final” firing

Kilns

Ovens used to fire clay

1. Pit kilns- (prehistoric)- simplest. Shallow pit dug in the ground. Made pots very fragile and porous.

Kilns2. 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.

Kilns4. 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

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

Clay Disasters

Kiln Firing Video