Pottery and Ceramic Clay
Firing Chart
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Pottery and Ceramics Definitions
All About The Clay
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TO BECOME HARD AND GLASS LIKE, CLAY MUST BE FIRED.
THIS MEANS THAT IT MUST BE BAKED IN A SPECIAL FURNACE, CALLED A KILN, TO A MINIMUM TEMPERATURE OF ABOUT 1112° F.
A kiln temperature can be measured in three ways:
KILN PEEPHOLE
The color of the kiln atmosphere.We look through the peepholes in the wall of the kiln and simply note the color inside.
The atmosphere in the kiln glows red at about 932° F, then turns orange to yellow to white as it gets hotter.
By 2372° F the atmosphere is white hot and damaging to the naked eye.
PYROMETER
This is a thermometer capable of registering high temperatures.CONES
Cones are the most accurate method because they measure the effects temperature has on the clay over time, the working temperature.Often clays and glazes are referred to by the Cone number to which they are best fired, such as, a Cone 9 glaze or a Cone 8 porcelain, and so forth.
The Cones themselves are small pieces of specially formulated clay which begin to melt at specific temperatures.
They are placed inside the kiln so that they can be seen when one looks through the peepholes while the kiln is being fired.
When the Cone begins to melt and bend over we know that the specific temperature has been reached.
WHAT HAPPENS AS CLAYS AND GLAZES ARE FIRED
212° F
Water boils.212 to 392° F
Pottery and Ceramic Firing Chart
Clays loses water.
392° F
Typical kitchen oven baking temperature.705° F
Chemically combined water leaves clay.932° F
Red glow in kiln.1063° F
Quartz inversionSLOW, CAREFUL FIRING UNTIL
1112° F
1472° F
Cone 015Organic matter in clay burns out.
1472 to 1832° F
Cone 015 to Cone 07Orange color in kiln.
Low fire earthenwares and lowfire lead glazes mature.
Normal firing temperature for red bricks and terra cotta pots.
1832 to 2120° F
Cone 07 to1Yellow color in kiln.
High fire earthenwares mature.
Feldspars begin to melt.
2138 to 2174° F
Cone 3 to 4Bright yellow white color in kiln.
Mid-range clays and low fire stonewares mature.
High iron content clays begin to melt.
2282 to 2345° F
Cone 7 to 9White color in kiln.
Stoneware clays vitrify, feldspathic glazes mature.
2345 to 2462° F
Cone 9 to 13High fire stonewares, porcelains vitrify.
MOST STUDIO POTTERY IS FIRED TO CONE 9 OR LOWER.
3113°
Silica melts3722°
Alumina melts
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