Set witness cones in a cone pack
Pyrometric cones tell you what the kiln actually reached, not just what the thermocouple says. They measure heat work (time × temperature), which is what matters for glaze melting.
The exercise
Set up a cone pack with three cones:
- Guide cone: one cone below your target (e.g., cone 5 if firing to cone 6). Should bend fully.
- Firing cone: your target cone. Should bend to the "6 o'clock" position.
- Guard cone: one cone above target. Should remain standing.
Placement
- Place the cone pack on a kiln shelf visible through the peep hole
- Cones should be angled at 8° from vertical (leaning slightly toward the next cone)
- Space them so a bending cone doesn't lean on its neighbor
What you're confirming
If the guide is flat, firing cone is at 6 o'clock, and guard is standing, your kiln hit the target perfectly. If not, you know exactly how far off you were.