Your controller says the kiln hit cone 6. But did the ware actually reach cone 6? Those aren't always the same thing, and witness cones are how you find out. If you've never used them, they're the cheapest insurance in the studio.
A thermocouple reads temperature at one point. But cones measure heat work, the true combination of temperature and time your pots experienced. Thermocouples drift with age, kilns have hot and cool spots, and a fast schedule can under-fire even when the display looks right. A witness cone shows you what actually happened to the glaze.
| Term | What it is |
|---|---|
| Witness cone | A single cone placed on the shelf to read after firing |
| Cone pack | Three cones (target, one lower, one higher) for a clearer picture |
A three-cone pack is the standard: the cone below your target should be fully melted, the target cone bent to touching the shelf, and the cone above still standing. That tells you that you hit your number and didn't overshoot.
Run a cone pack any time results look off, when you get a new kiln, after replacing elements or a thermocouple, and periodically as a health check. If your target cone consistently comes out underfired despite a correct display, your thermocouple is likely drifting and it's time to recalibrate or replace it.
A drifting thermocouple or worn elements are the usual culprits, and both are fixable. Call or text me, Spencer, at (801) 839-5882 for the right replacement parts.
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