Wednesday, July 8, 2015

Clay Firing Schedule - Firing Procedures, Temperatures, Orton Cone Charts

Note - When purchasing clay or glaze, check the temperature requirements and make sure your kiln will fire them correctly, and that its temperature range is compatible with the clay you are using. Always test fire clay/glaze combinations using small test tiles before using glaze on artworks. Pyrometric Cone Chart (Orton Standard) When heated at 150 degrees C/hour:

Cone No. Centigrade Fahrenheit
Cone No. Centigrade Fahrenheit
022 600 1112
04 1060 1940
021 614 1137
03 1/2 1080 1976
020 635 1175
03 1101 2014
019 683 1261
02 1120 2048
018 717 1322
01
1137
2079
017
747
1376

1
1154
2109
016
792
1457

2
1162
2124
015
804
1479

3
1168
2134
014
838
1540

4
1186
2167
013
852
1565

5
1196
2185
012
884
1623

6
1222
2232
011
894
1641

7
1240
2264
010
900
1652

8
1263
2305
09
923
1693

9
1280
2336
08
955
1751

10
1305
2381
07
984
1803

11
1315
2399
06
999
1830

12
1326
2419
05
1046
1914

13
1346
2455








Low-Fire
Mid-Fire

High-Fire
Some Porcelain

Earthenware
Stoneware

Kaolin (China Clay)


Firing Schedule #1 - Digital Kilns: This Schedule can be followed for kilns with a temperature gauge and timer:
  1. 80 degrees an hour to 180; hold for 3-4 hours - this step is critical to keep the clay from exploding once you begin to raise the temperature.
  2. 150 degrees an hour to 500; hold for ten minutes.
  3. 200 degrees an hour to 1000; hold for ten minutes.
  4. 300 degrees an hour to the desired temperature is reached; end of firing.


Firing Schedule #2 - Kiln Sitters: My kiln is an old Gare model kiln with a model K kiln sitter. My method for firing is as follows: 

fire kiln, orton cone charts, firing charts
  • Note - this kiln has an extra ring with its own element (the top section with the extra switch). While this is great for enlarging the firing chamber to fit more artworks, it reduces the firing temperature from cone 10 to cone 8.
  • The first step before firing the sculpture in the kiln is to warm the sculpture to approximately 120 to 200 degrees F to remove all of the water from the clay. The sculpture is placed in a drybox (little or no humidity) consisting of a small heater or several light bulbs (about 15-20 100 watt bulbs) for about 3-5 days. This step is critical to keep the clay from exploding once it is put in the kiln.
  • The sculpture is then placed in the kiln. The bottom switch is turned on with all peep holes open and the lid propped up for two hours.
  • The next higher switch is turned on and left for an hour.
  • The next higher switch is turned on, the lid closed, and the bottom peep hole is closed. The top peep hole is left open to circulate air properly throughout the kiln and help protect the metal portions (thermocouple, elements, etc) from gasses that can damage them. This is especially important for reduction-type firing,which is caused by a lack of oxygen in the kiln chamber. When firing a sculpture that still has newspaper in it, it is a reduction firing because the burning paper reduces the amount of oxygen in the chamber.
  • The next 3 switches are turned on consecutively each hour until the kiln automatically shuts off.
  • The kiln is left overnight to cool before the lid or peep holes are opened. Opening the kiln too quickly will crack or break the sculptures due to stress from quick temperature changes.
fire kiln, orton cone charts, firing charts

No comments:

Post a Comment