The primary way to test if an electric kiln fire reached the desired temperature, especially in ceramic firing, is by using pyrometric cones.
Pyrometric cones are small, slender pyramids made from carefully formulated ceramic materials. They are designed to bend and melt at specific temperatures under specific heating rates, providing a visual indication of the "heat work" inside the kiln – the combined effect of temperature and time.
Using Pyrometric Cones for Testing
To test your electric kiln fire using cones, you typically place a set of cones inside the kiln where they can be viewed through a peephole during the firing or examined afterward.
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Cone Placement: Place the cones upright in a cone holder. Position the holder within the kiln, ensuring the cones are:
- At least 2 inches away from the kiln wall. This prevents the cones from being affected by direct radiant heat from the elements, giving a more accurate reading of the atmosphere's heat.
- Often placed near a shelf or another reference point.
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Observing the Firing: As the kiln heats up, the tip of the cone will begin to soften and bend. The firing is complete when the cone bends to a specific angle, typically when the tip touches the shelf or base it is placed next to.
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Interpreting the Results: After the kiln cools down, you can examine the cone(s) to evaluate the firing outcome:
Cone State Firing Result Indication Cone is bent Fired correctly The kiln reached the intended heat work. Cone hits Shelf Overfired The kiln went hotter or held temperature too long, exceeding the intended heat work. Cone is not bent at all Underfired The kiln did not reach the intended heat work.
By using multiple cones (e.g., a guide cone, the target cone, and a guard cone), you can determine if the firing was too hot, too cool, or just right. This method is a reliable way to verify that your ceramic pieces received the correct heat work necessary for glazes and clay bodies to mature properly.
