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Ceramics 1: Fire&Glaze
Transcript of Ceramics 1: Fire&Glaze
What are the steps
in the firing process?
What could possibly go wrong?
Pottery that has NOT been fired yet
Greenware must be bone-dry before it is fired!!
Bone-dry means free of moisture.
Ways you can tell if a piece is bone-dry...
pottery appears lighter in color
pottery feels warmer to the touch
1st firing which transforms the clay into permanent pottery
2nd Firing after glazes have been applied to the Bisqueware
Firing is the process of applying sustained heat to clay in order to change clay into permanent pottery or ceramics...
Clay has a flexible structure that make it plastic when mixed with water. Ceramics does not not have that quality it has a rigid structure.
That means that clay even when it is dry it can be turned back into clay again and again and again....
the truth is that in thousands of years when you are long gone your pottery will remain.
Even a big ugly pot is forever.
How is pottery fired?
Clay must be raised to the correct temperature to bring about this magical transformation
What is a
Basically a large oven or furnace that the clay is fired in...super important part of the clay creation process!
This is an electric kiln...
We are using a kiln like this!
about 1900degrees, the high heat creates a chemical change in the clay...making it similar to rock!
Clay is recyclable... Pottery is forever.
Inside the kiln are coils like these that heat up the pottery
But an electric kiln is a modern idea... there are all sorts of kilns
To do this, the unfired pottery is placed in a kiln and the temperature is gradually raised over a period of hours until it reaches the proper temperature
you can fire a pot almost anywhere
Pottery that has been fired once
How HOT does the kiln need to get?
FIRING: pyrometric cone
measuring the kiln temperature
It depends on what kind of clay or glaze you are firing
Low fire- earthenware (aprox. 1900 F)
High fire- porcelain (aprox. 2300 F)
How do you measure kiln temperature?
devices created to melt at specific temperatures and measure kiln temperature
Cones are not used as much any more because many kilns are digital...
cone is also used to describe the temperature a clay or glaze should be fired to
Example: Cone 05 (low fire)= 1900 F
Cone 5 (high fire)=
After the pottery is bisque fired glaze can be applied by dipping, spraying, or painting them on the surface of the pottery
glass and chemical colorant mix)
a form of glass that will fuse to the surface of the clay used to decorate and waterproof pottery
Glaze test tiles-matte and shiny
Glazes are NOT paint...
they can be layered, drizzled, and dripped
but they are not made to be mixed...
Yellow and Blue will not necessarily make Green
they are dull when they are applied and often do not even look at all like the color you expect until after they are fired
Shrinkage & Warping
CONSTRUCTION AND FIRING CONSIDERATIONS
How to avoid project blow ups in the kiln...
1.Avoid trapping air pockets in the clay
-clay is a great material to make art from, as long as you remember a few simple rules...for success!
-air gets heated, expands, boom
2.Avoid putting wet clay in the kiln
-water in the clay, when heated up, turns to steam, with no place to escape...boom
3.Avoid drastic temperature changes
-we can't fire the kiln in an hour, it's going to 1900 degrees for goodness sake! If we crank the temp too fast, boom
wet clay is darker in color like this...
and cool to the touch
dry clay is called greenware...
it is light in color, not cool to the touch
ground up fired pottery, because it is already fired it doesn't shrink...so when added to clay it reduces shrinkage...you'll notice it in the clay we use!
Notice the change in color @ each stage!
Glazed & Finished
WHY IS MY POT SO LITTLE?
-as pottery is dried and fired it loses volume due to all the lost water... this is called
the rate clay reduces in size as it is fired into permanent ceramics
-different clay bodies have different shrinkage rates depending on their characteristics.
Rememeber those annoying little bits in your clay that made it difficult to smooth out your pottery.... that it added to the clay to reduce shrinkage and help control warping.
a uneven drying problem that causes pottery to be distorted as it dries and is fired.
-Note: warping is usually a result of uneven thickness in the clay
bits of ground up fired pottery added a clay body to reduce shrinkage and warping
-grog makes the clay more stable during the process because it doesn' t change...