In standard firing,
cones of the correct number are placed around the kiln and are
watched. When the cones fall the kiln is turned off. This
works the same for gas and electric kilns.
Electric kilns with electronic controllers (such as the Skutt KilnMaster
series) have a
thermocouple which continuously measures the temperature, records it
over time, and shuts off the kiln when the appropriate heat absorption has been
met. So if the ramping temperature is fast, the kiln will go to a
higher temperature before it turns off than if the ramping temperature
is slow (thus allowing the clay to absorb more heat along the
way.) The final temperature is most affected by the rate of
temperature increase over the last 300 to 400 degrees of firing.
Note: Think of the 0 in a cone number as meaning "minus".
So 06 is much cooler than 6 because it is like a "minus 6".
Typcically it takes 15-25 minutes
for a cone to bend once it starts. This depends on the cone
number. The cone bends slowly at first but once it reaches the
half way point it bends quickly. When the cone tip reaches a point
level with the base, it is considered properly fired.
If a cone is soaked at
a temperature near its equivalent temperature, it will continue to
mature, form glass and bend. The time for the cone to bend depends on
several factors and as a general rule, a 1 to 2 hour soak is sufficient
to deform the next higher cone number. A soak of 4 to 6 hours will be
required to deform two higher (hotter) cones.