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Intro to Ceramics/Clay. Clay Makes up 75% of the earth’s land mass!!. 3 Properties that make up clay. 1. Plasticity (ability to form). 2. Porosity (ability to hold moisture). *Similar to a sponge. 3. Vitrify (ability to harden and keep its shape). 3 types of clay.

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Presentation Transcript
3 properties that make up clay
3 Properties that make up clay

1. Plasticity (ability to form)

3 types of clay
3 types of clay

Clay is characterized by it’s iron content (color), vitrification process, and firing temperature.


-low fire temperature (1800 degrees), red in color, often used to make Mexican pottery and flowerpots.


-medium fire temperature (up to 2200-2300 degrees), tan or buff in color, often used to make everyday dished, mugs, etc.


-high fire temperature, white in color, often used to make dolls, China dished, toilets, sinks

wedging clay
Wedging clay

-removes the air bubbles

-prepares and aligns the platelets in the clay

-develops a uniform texture

-----When building objects with clay, it is important not to trap air inside the clay. This will cause the piece to explode in the kiln.

3 steps to attach clay
3 steps to attach clay

Score- lightly put in hatch marks

on both pieces to be attached

Slip- (liquid clay) add this muddy

substance to both of pieces of

clay you are attaching

Weld- put the two pieces together

and blend, it is sometimes necessary

to add an additional coil to the seam

to make it stronger


- Any clay that has not been fired in the kiln is considered greenware

3 stages of greenware

Workable- clay is very moist and pliable


Leatherhard- clay is still

somewhat moist and easily

be carved but breaks easily

when bent

Bone dry-clay is lighter in

color and warm to the touch

cracking and warping
Cracking and Warping

--Your clay piece can crack or warp when it dries.

  • Uneven moisture
  • Uneven drying
  • Uneven thickness
  • Drying too quickly


Pottery Wheel



BatNeedle Tool

Loop, Carving, trimming Wire cutter

firing pottery
Firing Pottery

Electric Fire

Pit fire

Wood Fire

Kiln- oven like machine that “fires” (bakes) the pottery

Raku fire

Gas Fire

firing pottery cont
Firing Pottery cont…

Bisque Firing- 1st firing,

about 1750-1800 degrees.

When it comes out of the kiln

it is called bisqueware

Glaze Firing- 2nd firing,

anywhere from 1800-2300 degrees.

When it comes out it is called


--It takes about 2 days to go through a full firing cycle.

--Clay looses it’s plasticity after it has been fired, and can NOT be (recycled) or reused at this point.

5 stages in the firing cycle
5 stages in the firing cycle
  • Water smoking- occurs when the temperature in the kiln reaches 212˚F, all remaining surface wateris burned off, enough steam is often generated to be seen. Hence the term water smoking. Water boils and turns to steam at 212˚F. If the steam leaves the clay too fast, the pot explodes just like if you boil eggs too fast, they crack.

Dehydration-660˚F, the chemical water, starts to burn off, by 950˚F the clay is completely dehydrated. It is now a chemically different material than it was when put into the kiln. Now it is aluminum silicate known as mullite. The change is non reversible.

  • Quartz Inversion - 1000°F. The quartz crystals in the clay undergo a change called the quartz inversion. The crystals grow and change in shape.
  • Oxidation- the burning off of organic materials occurs at 1600°F to 1700°F. This has no chemical effect on the clay, but it does leave the clay more porous.
  • Vitrification- Partial vitrificationbegins as the temperature rises. This will be determined by the type of clay body. Clay with a high alumina content (stoneware and porcelain) will vitrify more slowly and at a higher temperature than clay high in fluxes such as iron or talc (earthenware). Vitrification, you will remember, is melting of the clay platelets. Complete vitrification results in a glasslike material; therefore, clay ware is never completely vitrified.
glazing and finishing
Glazing and Finishing

Glaze-glass like coating put on pottery to make it waterproof, melts when fired, hardens as it cools

Glaze application techniques:

  • Dipping

2. Spraying

3. Pouring/dripping

a little art history
…a little art history
  • The Chinese discovered

wood ash floating through the

kiln and when it landed on the

pottery it created a shiny

surface (but isn’t considered

real gaze)

  • The Egyptians were the first

to use true glazes since about

5000BC. They dug their clay

from the Nile river and used

sand from the desert to make


ingredients of glaze
Ingredients of glaze
  • Glass former – (silica or sand) creates the glossy surface,  silica forms glass all by itself. However, silica melts at about 3100⁰ F, which is much too hot for ceramic kilns. As such, it cannot be used on its own.
  • Flux – aids melting, keeps surface of pottery from oxidizing so the glaze can attach, lowers the melting point of the silica.
  • Refractory (alumina) – resists melting, aids in high temperature firing, stiffening agent.
glazing tips
Glazing Tips
  • Keep a “dry foot”. (no glaze

on the bottom) Why???

  • Use a pencil (regular #2,

not a mechanical) to draw a

thick line around the bottom

of the glaze edge. Why??

  • Glaze “takes” best on the first

firing. Why??

  • Dip glazes once, (unless it’s thin

enough, or you are crossing colors).


  • Brush 2 or 3 layers. Apply coats as

soon as the sheen of the coat before is

disappearing. Why??

other ways to finish your piece
..Other ways to finish your piece
  • Burnish- “to polish by

rubbing to a high sheen” Often

with pottery, a slip is applied to

the surface of the clay when it is

in the late leather-hard stage then

polished with a smooth rock or


  • Sgraffito- a colored slip

is applied and often burnished

to the pottery surface then a

design is etched or carved out

of the applied slip.

o ther ways to finish your piece cont
…other ways to finish your piece cont...


Photo transfer

Slip trailing

Glaze transfers