The fire, which is at this point built directly on the floor of the main firebox,
is slowly increased in intensity, always with the mind to the effects this increase
is having on each of the five chambers of wares. The complexity of firing this style
of kiln is enormous. In effect, you re firing five kilns at once, all with inter-relating
controls and effects on each other. Fire too fast and you can create rain in the
last chamber! Burn too much wood relative to the airflow at the wrong time, and
you can cause massive firing defects in another chamber.
As the temperature gradually climbs in the first main chamber, successive chambers
are also monitored so that they are firing correctly, As more heat energy is required,
the fire is moved off the main firebox floor and up onto a grate structure to allow
better combustion. Air ports are opened and closed as needed to maintain proper
conditions of the fire in each chamber. The type and size of the pieces of wood
being stoked is constantly being varied based upon the condition of the fire in the
kiln. Eventually, after about 24 hours of continuous and careful stoking, the first
main chamber has reached approximately 2400 °F, and the wares there are finished.
Stoking on this main firebox then ceases, and the stoking operation moves to the
stoke hole on the side of the kiln that allows wood to go into the firebox in chamber
number two. Great care must be exercised so as to hold the kiln back at this point.
Slight inattention can result in a very rapid temperature rise, ruining the wares.
As the coals in the main firebox burn off, the stoking ports and air inlets into
this area are carefully sealed off with clay. After about 3 to 4 hours of stoking
in chamber number two, the chamber is completed.
The process is then continued along up the hillside, until all chambers are completed.
The kiln is then sealed, and an exhausted John can go to bed.
The slow 10 hour overnight pre-heat on the small propane burner brings the main firebox
and first chamber up to about 350 °F. This time is used for a good night’s sleep
before the real sustained and hot work of the wood firing begins. Typically the
kiln is shifted over from the gas pilot burner to a low wood fire at about 5 AM.
By then steam is coming off of the first chamber.