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Pyrometric Cones are used as witness cones to monitor ceramic firing in all types and sizes of kilns for consistent, repeatable firing temperature. They are made of specifically formulated compositions, including many of the same ingredients as ceramic products. Each cone is designated a number (for example, cone 04), and each cone number measures a fairly small range of firing temperature.
How do they work?
When the kiln temperature reaches the range a cone number is designed to melt in, the tip of the cone begins to bend. The final degree of cone bending depends on the last 100°C (180°F) of the firing profile and temperature, but this significant bending may represent a change over only a few degrees of temperature. Pyrometric cones are therefore valuable for verifying that your kiln is delivering the expected amount of heat work within the kiln ware load at specific temperature and profile settings.
Moreover, while kiln shut-off devices and electronic controllers can drift from their set point over time even though everything appears to be normal, pyrometric cones do not. They will indicate whether kiln firing is under control or subtle changes are occurring, thereby giving you time to take corrective action before these changes impact your ceramic ware.
To determine the best maturing temperature for your ware, we recommend that you use three cones for firing: one cone for the desired maturing temperature, one cone right below that temperature, and one cone right above it.