St. Earth Pottery | Process


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Process: Soda Firing: Catenary Kiln Here are photos of a soda firing I did in May, 2002 with some descriptions of the process. The kiln is a catenary arch design, with two natural gas, forced air burners. It was sited outside the old ceramics facility at DePauw University, and was torn down in 2004 when the Art department moved to a new building. The kiln was initially built with other purposes in mind, but adapted to soda firing quite well (the main drawback being too few ports for spraying the soda). It reached cone 10 in 9-10 hours. The cross-draft path of the flame created good directional soda distribution and flashing effects. However, after about 10 firings, the arch started shifting outward, which caused problems with the interior castable lining and the fit of the cast door blocks. For long-term stability, a metal frame might be required to hold the arch in position. Results from this kiln can be seen in the Archive Gallery.

Preparing to load, castable door removed at left	All shelves and supports are coated with kiln wash to resist the soda

This kiln holds about 50 pots, packed loosely enough to allow the soda to work into the stack	Fully loaded and preparing to brick up the door

The door is made of 10 castable sections	Several hours into the firing, both burners are running on high

The firing kiln; with powered burners, the stovepipe stack provides sufficient draft	About 4# of soda solution are sprayed into the kiln (50/50 soda ash/baking soda)

A pressurized garden sprayer is used to add soda	Soda is sprayed in two rounds, at cone 9 and just before shutting down

Completed firing, ready to cool overnight	The results show a variety of slips and glazes