A cone measures heatwork, not just temperature
Pyrometric cones bend as they absorb heat over time. Orton describes this as heatwork, the combined effect of time and temperature. That is why the chart has three columns: the faster the kiln climbs during the last 180 °F (100 °C), the higher the temperature at which the cone bends.
Reading the chartThe middle column (108 °F or 60 °C per hour) is the one most often quoted. Cone 6 is 2,232 °F (1,222 °C) at that rate, but 2,165 °F on a slow climb and 2,269 °F on a fast one.Source: Orton Ceramic Foundation
The cones most home potters use
| Cone | Typical use |
|---|---|
| 06–04 | Bisque firing; low-fire glazes and underglazes |
| 06–01 | Earthenware and other low-fire clay bodies |
| 5–6 | Mid-range stoneware and porcelain, most cone 6 glazes |
| 10 | High-fire stoneware and porcelain |
Your clay and glaze labels name the cone they are made for. Fire both to the same cone, or follow the maker’s separate bisque and glaze cones.
Witness cones, sitters and controllers
- Orton notes that small cones deform about 7–10 °C (12–18 °F) earlier than self-supporting cones.
- A cone in a kiln-sitter shutoff does not always give the temperature on the chart, so Orton recommends confirming results with a cone on the shelf.
- Soaking near the end temperature keeps cones bending: Orton says a 1–2 hour soak is usually enough to bend the next higher cone.
- Digital controllers read a thermocouple, which drifts with age. A witness cone shows the heatwork the ware actually got.
A red flag for budget furnaces
Many inexpensive plug-in “kilns” are listed with a 2,192 °F (1,200 °C) maximum. On Orton’s chart cone 6 needs 2,232 °F at a medium rate, so a furnace that tops out at 2,192 °F cannot reach cone 6 that way. Check the cone rating, not just the temperature.
Questions
What temperature is cone 6?
For a regular self-supporting Orton cone, 2,232 °F (1,222 °C) at a 108 °F (60 °C) per hour final heating rate. It is 2,165 °F at 27 °F per hour and 2,269 °F at 270 °F per hour.
What temperature is cone 04?
1,945 °F (1,063 °C) at the medium rate, a common bisque and low-fire glaze temperature.
What temperature is cone 10?
2,345 °F (1,285 °C) at the medium rate, and 2,284 to 2,381 °F across Orton’s slow to fast rates.
Why does the 022–020 slow column show a dash?
Orton’s chart does not list slow-rate values for those cones, so we leave them blank rather than estimate.