Cone chart: Orton and SK cones

Orton cones

Orton's older chart for large cones heated at 150 °C an hour over the last 100 °C, as kiln makers reprint it; Orton's current figures for large cones at that rate differ from it by up to 19 °C. Orton publishes no figure above cone 14, and this chart none above cone 15. Cones measure heatwork, not temperature: set a witness cone.

Source: Temperature equivalents for Orton standard pyrometric cones (as determined at the National Bureau of Standards), as reprinted by W P Dawson Inc (©2000). Open the reprint

Orton also makes cones from 16 to 42. Orton publishes no temperature for them, and no chart we found gives one, so none is shown: 16, 17, 18, 19, 20, 21, 23, 26, 27, 28, 29, 30, 31, 31.5, 32, 32.5, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42.

Orton's own current figures

Orton's chart of 2016 for cones 022 to 14 gives a temperature for each heating rate, over the last 100 °C of the firing. The figures differ a little from the chart above, which Glazecalc uses for cone checks.

Large cones 13 and 14 are made differently, with their own temperature equivalents. Rates are over the last 100 °C of the firing. Large cones 13 and 14 have different compositions and different temperature equivalents; Orton publishes no figure above cone 14.

Source: Temperature Equivalents for Orton Pyrometric Cones (°C), Cone Numbers 022-14, The Edward Orton Jr. Ceramic Foundation, 2016. Open the chart

SK cones

SK (Seger) cones are sold in Japan under the standard JIS R 8101:1999. The figures are the standard's reference temperatures as a seller prints them, not what a kiln will show.

The standard gives reference temperatures. At a potter's rate of about 100 °C/h, Kyoto's municipal institute measured its own Kyoto cones bending 47–79 °C cooler than the JIS figure for the same number; we found no such measurements for SK cones to JIS. Set a witness cone and compare.

Source: 有恒商事株式会社, table of standard melt-down temperatures. Open the table