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 NoSSB SSSB MSSB FSSK SSSK MSSK FLRB MLRB FIFB MIFB F
022-586590-------
021-600617-------
020-626638-------
019656678695---676693--
018686715734---712732--
017705738763---736761--
016742772796---769794--
015750791818---788816--
014757807838---807836--
013807837861---837859--
012843861882---858880--
011857875894---873892--
010891903915871886893898913884891
009907920930899919928917928917926
008922942956924946957942954945955
007962976987953971982973985970980
00698199810139699919989951011991996
005½100410151025990101210211012102310111020
0051021103110441013103710461030104610321044
0041046106310771043106110691060107010601067
0031071108611041066108810931086110110871091
0021078110211221084110511151101112011021113
0011093111911381101112311341117113711221132
11109113711541119113911481136115411371146
2111211421164---11421162--
31115115211701130115411621152116811511160
4114111621183---11601181--
5115911861207---11841205--
5½116712031225-------
6118512221243---12201241--
7120112391257---12371255--
8121112491271---12471269--
9122412601280---12571278--
10125112851305---12821303--
11127212941315---12931312--
12128513061326---13041324--
13131013311348---13211346--
14135113651384---13881366--

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
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