Note on Kiln Firing Chart and Orton Cone Charts – 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/glaze you’re using according to standard orton cone charts. It’s advisable to test fire clay/glaze combinations using small test tiles or rejects before using glaze on higher quality artworks. Firing at a temperature above what your clay/glaze is rated for on the orton cone chart will result in ruined and runny glazes (which will stick to your kiln shelves), over-fired artworks that can slump, crack, or shrink – basically it will ruin your work!
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Kiln Firing Chart: Pyrometric Cone Chart (Orton Standard) or Orton Cone Chart:
Kiln Firing Chart #1 – Digital (Automatic) Electric Kilns:
This Schedule can be followed for kilns with a temperature gauge and timer:
- 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.
- 150 degrees an hour to 500; hold for ten minutes.
- 200 degrees an hour to 1000; hold for ten minutes.
- 300 degrees an hour to the desired temperature is reached; end of firing.
Kiln Firing Chart #2 – Electric Kilns with Kiln Sitters:
My kiln is an old Gare model kiln with a model K kiln sitter. My method for firing is as follows:
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, along with a pyrometric cone placed in the thermocouple that matches the orton cone chart temperature you plan to fire to. 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.
Kiln Firing Chart – Firing an Older Kiln With Switches Step 2:
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Kiln Firing Chart: Kiln Safety
Kiln safety is something to consider. Placement of your kiln, surface protection from heat, and ventilation should all be top priority. With my old Gare I used kiln safety screens to protect the surfaces around my kiln from getting too hot. I didn’t have a ventilation system, so I opened up windows, doors, etc. and didn’t stay in my studio while the kiln was firing – especially in the beginning when the newspaper was burning out.
I intend to put a ventilation system on my next kiln to help with fumes. When you get your kiln, read the instruction that come with it (or look up the instructions online for an older kiln) – kilns can be dangerous and care is needed when using them.
Kilnsitters, Orton Cones, and Timers:
My pics above show kiln switches, which you don’t often see on newer kilns. Pyrometric cones (orton cones) and bars are a necessity with older kilns like my Gare, but while you still need the orton cone charts to help determine your firing temperatures, you don’t have to have a pyrometric cone for firing (though “witness cones” can help make sure your kiln is firing at the proper temperature).
Kiln Shelves and Furniture:
Last but not least, you can never have too many shelves or supports! Every firing is different, and the more options you have for shelving, the more artworks you can fit in a single firing. It’s never fun to have a full kiln and one piece still sitting outside the kiln, especially if an extra shelf would have fit that extra piece in.