[ Home ] [ Up ] [ cone temperatures ]

Pyrometric cones are used to determine the combined effect of temperature and time - called "heatwork"- in the firing of ceramics.
Since pyrometric cones were first invented and produced by Dr. Hermann Seger in 1886, other manufacturers have emerged and "Seger" cone has become a generic term.
Orton Cones are made in the form of trigonal pyramids from raw materials used in the manufacture of many ceramic products. They are calibrated to collapse at different temperatures - the 37 cone numbers each represent a different amount of heatwork. Cones are therefore considered more effective indicators of a completed firing cycle than a pyrometer as they depend on the combination of time and temperature, rather than temperature alone.
In practice a variety of firing rates are used and therefore all users are recommended to carry out their own checks under their own firing conditions.
The evenness of heat distribution throughout a kiln can be checked by using several sets of cones set in different positions throughout the kiln- e.g. back front: top- bottom-centre.
MINI CONES
These small cones are used in kiln sitters. The tapered shape of the cone allows the potter some flexibility in adjusting the shut off point. They are also excellent for use in smaller kilns where space is at a premium.
STANDARD CONES
These cones are used in a Cone Stand and are widely used for visually checking the firing process and to monitor the conditions within a kiln.
Correct Cone Placement
To ensure accurate temperature indication cones must be set in the following manner
To place cones correctly into the cone stand make sure they sit flat on the base and lean at an 8° angle over the flat side in the holder. As proof of correct positioning, when looking at the holder and the cones are leaning to the left, the cone numbers should be showing on the front right hand side of the cone.

The Three Cone System
While  a single cone may be used on a shelf to "witness" the firing, it is recommended to use three different cones. The group consists of a Firing Cone-the desired cone for the ware being produced, the Guide Cone -one cone number cooler and the Guard Cone-one cone number hotter than the Firing Cone. These cones need to be set deep in the kiln, yet should be visible through the bung hole.
When the Guide Cone starts to bend, the ware is approaching maturity. The bending of the Firing Cone indicates that the firing is at its correct stage. If the Guard Cone has bent, the firing has passed its best time-temperature window.