Measuring Heatwork & Temperature with Orton Cones

What are cones?

Firing ceramics in a kiln is a bit like cooking a pizza in the oven. As with Italian wood-fired stoves, you could set your oven on very high heat and cook the pizza in just four minutes. Or you could cook the pizza for a longer amount of time at lower heat. Either way, you’ll end up with edible pizza.

Pyrometric cones are a measurement of the total amount of heatwork. Heatwork is the combination of time and temperature. We can say that two pizzas received a similar amount of heatwork if they are both fully cooked, even if they were cooked at different temperatures for different durations of time. Similarly, we can say that two ceramic vases were fired to a certain cone (e.g. similar amount of heatwork) even if the firings were different in temperature & time.

It’s important to note that firings are often uneven: a kiln may have cool and hot spots, and the difference in temperature may be one or more cones. Just because a cone has fallen doesn’t mean the entire kiln (including the ceramics and kiln furniture) has also reached that cone temperature. So it’s a good idea to sometimes place extra cones throughout the kiln to determine if the firing is even.

For more information on cones, see the excellent Digitalfire article
Interpreting Orton Cones as well as Orton’s Pyrometric Cones Resources.

Setting & Reading Cones

The quantity of cones and cone packs as well as their arrangement and placement vary from potter to potter, kiln to kiln. The following is only one approach.

There are a number of different cone manufacturers. Each brand has unique cone formulations and firing characteristics. Cone numbers between brands may be quite different, for instance the Chinese “Seger” cone 9 is approximately Orton cone 12. Even when cone numbers between brands are rated for the same temperature, actual firing behaviour may be quite different. Glazy recommends using Orton cones as they seem to be the most reliable and accurate.


Breaking apart pairs of Orton cones using a cylindrical support.


Length of large cones above cone plaque.

According to Orton:

“Large Cones are normally mounted so exactly 2” of the cone is exposed above the top of the cone plaque or clay pat. Small Cones are mounted so that 15/16" of the cone is exposed above the top of the plaque or pat."

Measure your cones and memorize how deeply they should be mounted.


After flattening a coil of clay, push cones downwards so that the angle is identical with a cone placed directly on the flat surface.


Wet cone packs can explode. Make your packs in advance or poke holes into the pack to let steam to escape.

This cone pack is for an Orton cone 10 firing.

The guide cone 9 will alert us when we are close to temperature.
The guard cone 11 will let us know if we are beginning to overfire.

While more expensive, pre-made cone plaques and self-supporting cones eliminate height and angle inconsistencies.


For mid and high fire, a “boat” is made to catch low-temperature cones. This boat is a folded slab.


Viewing low-temperature cones in the kiln at about 900°C. Cone 010 is bending, while 08, 1, and 3 have not moved. It’s advisable to place cone packs at the top and bottom of your kiln in order to understand and control temperature differences while firing.


A cone pack after firing. In this firing, once cone 9 fell to 5 o’clock the kiln was intentionally stalled. Even though the temperature did not rise, cone 10 completely fell after about one hour. Cones measure heatwork, the effect of both temperature and time.

template
The Orton Cone Template can be used to determine the degree of deformation for Orton cones.


Inexpensive Chinese cones. Cones 7 and 9 are down, but cone 8 is still standing. The entire box of cones should be thrown away. But which cone is defective, 8 or 9? Compared to the cost of a firing and the work inside, the cost of cones is negligible. Buy the most reliable cones you can find.

Download PDF chart of Orton Cone positions:
Color (566.2 KB)
A4 Black & White (78.2 KB)

Viewing Cones

Warning: Prolonged or cumulative long-term exposure to infrared and ultraviolet light can seriously damage your eyes.

ANSI-compliant infrared and ultraviolet eye-protection glasses are a must when viewing
inside the kiln at high temperatures.

Sunglasses that only filter ultraviolet light are NOT sufficient.

For more information, see Eye Protection in the Pottery Studio

There are many tricks for seeing cones more clearly inside the kiln.

The simplest method is using a high-intensity LED flashlight with an output of at least 400 lumens and a focused beam.


#5 welding goggles and 2000 lumens LED flashlight.

Temperature Equivalent Charts for Cones

References:

Orton Pyrometric Cones Celsius (°C)

Self Supporting Cones Large Cones Small Cones
Regular Iron Free Regular Iron Free Regular
Heating Rate ̊C/hour (last 100 ̊C of firing)
Cone 15 60 150 15 60 150 60 150 60 150 300
022 586 590       N/A N/A     630
021 600 617       N/A N/A     643
020 626 638       N/A N/A     666
019 656 678 695       676 693     723
018 686 715 734       712 732     752
017 705 738 763       736 761     784
016 742 772 796       769 794     825
015 750 791 818       788 816     843
014 757 807 838       807 836     870
013 807 837 861       837 859     880
012 843 861 882       858 880     900
011 857 875 894       873 892     915
010 891 903 915 871 886 893 898 913 884 891 919
09 907 920 930 899 919 928 917 928 917 926 955
08 922 942 956 924 946 957 942 954 945 955 983
07 962 976 987 953 971 982 973 985 970 980 1008
06 981 998 1013 969 991 998 995 1011 991 996 1023
05 1/2 1004 1015 1025 990 1012 1021 1012 1023 1011 1020 1043
05 1021 1031 1044 1013 1037 1046 1030 1046 1032 1044 1062
04 1046 1063 1077 1043 1061 1069 1060 1070 1060 1067 1098
03 1071 1086 1104 1066 1088 1093 1086 1101 1087 1091 1131
02 1078 1102 1122 1084 1105 1115 1101 1120 1102 1113 1148
01 1093 1119 1138 1101 1123 1134 1117 1137 1122 1132 1178
1 1109 1137 1154 1119 1139 1148 1136 1154 1137 1146 1184
2 1112 1142 1164       1142 1162     1190
3 1115 1152 1170 1130 1154 1162 1152 1168 1151 1160 1196
4 1141 1162 1183       1160 1181     1209
5 1159 1186 1207       1184 1205     1221
5 1/2 1167 1203 1225       N/A N/A     N/A
6 1185 1222 1243       1220 1241     1255
7 1201 1239 1257       1237 1255     1264
8 1211 1249 1271       1247 1269     1300
9 1224 1260 1280       1257 1278     1317
10 1251 1285 1305       1282 1303     1330
11 1272 1294 1315       1293 1312     1336
12 1285 1306 1326       1304 1324     1355
13 1310 1331 1348       1321 1346     N/A
14 1351 1365 1384       1388 1366     N/A

Orton Pyrometric Cones Fahrenheit (°F)

Self Supporting Cones Large Cones Small Cones
Regular Iron Free Regular Iron Free Regular
Heating Rate ̊F/hour (last 200 ̊F of firing)
Cone 27 108 270 27 108 270 108 270 108 270 540
022 1087 1094       N/A N/A     1166
021 1112 1143       N/A N/A     1189
020 1159 1180       N/A N/A     1231
019 1213 1252 1283       1249 1279     1333
018 1267 1319 1353       1314 1350     1386
017 1301 1360 1405       1357 1402     1443
016 1368 1422 1465       1416 1461     1517
015 1382 1456 1504       1450 1501     1549
014 1395 1485 1540       1485 1537     1598
013 1485 1539 1582       1539 1578     1616
012 1549 1582 1620       1576 1616     1652
011 1575 1607 1641       1603 1638     1679
010 1636 1657 1679 1600 1627 1639 1648 1675 1623 1636 1686
09 1665 1688 1706 1650 1686 1702 1683 1702 1683 1699 1751
08 1692 1728 1753 1695 1735 1755 1728 1749 1733 1751 1801
07 1764 1789 1809 1747 1780 1800 1783 1805 1778 1796 1846
06 1798 1828 1855 1776 1816 1828 1823 1852 1816 1825 1873
05 1/2 1839 1859 1877 1814 1854 1870 1854 1873 1852 1868 1909
05 1870 1888 1911 1855 1899 1915 1886 1915 1890 1911 1944
04 1915 1945 1971 1909 1942 1956 1940 1958 1940 1953 2008
03 1960 1987 2019 1951 1990 1999 1987 2014 1989 1996 2068
02 1972 2016 2052 1983 2021 2039 2014 2048 2016 2035 2098
01 1999 2046 2080 2014 2053 2073 2043 2079 2052 2070 2152
1 2028 2079 2109 2046 2082 2098 2077 2109 2079 2095 2163
2 2034 2088 2127       2088 2124     2174
3 2039 2106 2138 2066 2109 2124 2106 2134 2104 2120 2185
4 2086 2124 2161       2120 2158     2208
5 2118 2167 2205       2163 2201     2230
5 1/2 2133 2197 2237       2194 2233     N/A
6 2165 2232 2269       2228 2266     2291
7 2194 2262 2295       2259 2291     2307
8 2212 2280 2320       2277 2316     2372
9 2235 2300 2336       2295 2332     2403
10 2284 2345 2381       2340 2377     2426
11 2322 2361 2399       2359 2394     2437
12 2345 2383 2419       2379 2415     2471
13 2389 2428 2458       2410 2455     N/A
14 2464 2489 2523       2530 2491     N/A

This text and all user contributions to the Glazy & the Glazy Wiki are licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy.
Ceramic Materials Workshop Mighty Mud Mixer Gasworks NYC