Cones versus Temperature

The information here is on converting Orton cones to temperature (°C).

Each column contains a cone type and a rate of firing.

Cone types:
SSB - Regular self-supporting cone
SSK - Iron free self supporting cone
LRB - Regular large cone
IFB - Iron free large cone

Firing rates:
S - 15°C/hr
M - 60°C/hr
F - 150°C/hr
The rate is measured over the last 100°C, i.e. if the temperature is 1240°C, the firing rate would be calculated between 1140°C and 1240°C.

Cone No	SSB S	SSB M	SSB F	SSK S	SSK M	SSK F	LRB M	LRB F	IFB M	IFB F
022	-	586	590	-	-	-	-	-	-	-
021	-	600	617	-	-	-	-	-	-	-
020	-	626	638	-	-	-	-	-	-	-
019	656	678	695	-	-	-	676	693	-	-
018	686	715	734	-	-	-	712	732	-	-
017	705	738	763	-	-	-	736	761	-	-
016	742	772	796	-	-	-	769	794	-	-
015	750	791	818	-	-	-	788	816	-	-
014	757	807	838	-	-	-	807	836	-	-
013	807	837	861	-	-	-	837	859	-	-
012	843	861	882	-	-	-	858	880	-	-
011	857	875	894	-	-	-	873	892	-	-
010	891	903	915	871	886	893	898	913	884	891
009	907	920	930	899	919	928	917	928	917	926
008	922	942	956	924	946	957	942	954	945	955
007	962	976	987	953	971	982	973	985	970	980
006	981	998	1013	969	991	998	995	1011	991	996
005½	1004	1015	1025	990	1012	1021	1012	1023	1011	1020
005	1021	1031	1044	1013	1037	1046	1030	1046	1032	1044
004	1046	1063	1077	1043	1061	1069	1060	1070	1060	1067
003	1071	1086	1104	1066	1088	1093	1086	1101	1087	1091
002	1078	1102	1122	1084	1105	1115	1101	1120	1102	1113
001	1093	1119	1138	1101	1123	1134	1117	1137	1122	1132
1	1109	1137	1154	1119	1139	1148	1136	1154	1137	1146
2	1112	1142	1164	-	-	-	1142	1162	-	-
3	1115	1152	1170	1130	1154	1162	1152	1168	1151	1160
4	1141	1162	1183	-	-	-	1160	1181	-	-
5	1159	1186	1207	-	-	-	1184	1205	-	-
5½	1167	1203	1225	-	-	-	-	-	-	-
6	1185	1222	1243	-	-	-	1220	1241	-	-
7	1201	1239	1257	-	-	-	1237	1255	-	-
8	1211	1249	1271	-	-	-	1247	1269	-	-
9	1224	1260	1280	-	-	-	1257	1278	-	-
10	1251	1285	1305	-	-	-	1282	1303	-	-
11	1272	1294	1315	-	-	-	1293	1312	-	-
12	1285	1306	1326	-	-	-	1304	1324	-	-
13	1310	1331	1348	-	-	-	1321	1346	-	-
14	1351	1365	1384	-	-	-	1388	1366	-	-

Hold Times

Because it takes time for heat to travel into the centre of a piece of clay, you can reduce the top temperature and hold the kiln at that temperature for a while. Unless the glaze needs the higher temperature, this is more economical in electricity and less hard on the elements.
The guidelines Orton gives for this are as follows:

• Drop by 10°C and hold for 20 minutes
• Drop by 20°C and hold for 40 - 60 minutes
• Drop by 30°C and hold for about 120 minutes