Temperature and Heatwork

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 Pyrometric Cone 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.

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
• Digitalfire - Pyrometric Cones

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