Intro to Ceramics/Clay Clay Makes up 75% of the earth’s land mass!! - PowerPoint Presentation

Slide1

Intro to Ceramics/ClaySlide2

Clay Makes up 75% of the earth’s land mass!!Slide3

3 Properties that make up clay

1. Plasticity (ability to form)Slide4

2. Porosity (ability to hold moisture)

*Similar to a spongeSlide5

3. Vitrify (ability to harden and keep its shape)Slide6

3 types of clayClay is characterized by it’s iron content (color), vitrification process, and firing temperature.Slide7

Earthenware

-low fire temperature (1800 degrees), red in color, often used to make Mexican pottery and flowerpots.Slide8

Stoneware

-medium fire temperature (up to 2200-2300 degrees), tan or buff in color, often used to make everyday dished, mugs, etc.Slide9

Porcelain

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

dishes, toilets, sinksSlide10

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.Slide11

3 steps to attach clay

Score

- lightly put in hatch marks on both pieces to be attachedSlip- (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 strongerSlide12

Greenware

-

Any clay that has not been fired in the kiln is considered greenware3 stages of greenwareWorkable-

clay is very moist and pliable Slide13

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 touchSlide14

Clay shrinks 5-15 % when it dries and fires.Slide15

Cracking and Warping

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

Uneven moistureUneven dryingUneven thicknessDrying too quicklySlide16

Machines

Kiln

Pottery Wheel

Pug-millSlide17

Tools

Bat

Needle Tool Loop, Carving, trimming Wire

cutter Slide18

Firing Pottery

Kiln

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

Wood Fire

Electric Fire

Gas Fire

Pit fire

Raku

fireSlide19

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

glazeware.

--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.Slide20

…Part 2Slide21

5 stages in the firing cycle

Water smoking-

occurs when the temperature in the kiln reaches 212˚F, all remaining surface water is 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.Slide22

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 vitrification

begins 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

.Slide23

Glazing and Finishing

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

Glaze application techniques: DippingSlide24

2. Spraying

3. Pouring/drippingSlide25

Brushing/paintingSlide26

…a little art history

The Chinese discovered

wood ash floating through the kiln and when it landed on thepottery it created a shinysurface (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

glaze.Slide27

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.Slide28

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).

Why??

Brush 2 or 3 layers. Apply coats as

soon as the sheen of the coat before is

disappearing.

Why?? Slide29

..Other ways to finish your piece

Burnish- “

to polish byrubbing 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 spoon.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.Slide30

…other

ways to finish your piece cont...

underglaze

Photo transfer

Slip trailing

Glaze transfers