Soda glaze is produced when sodium compounds (typically sodium carbonate, sodium bicarbonate, sodium chloride or a combination) are introduced into the hot kiln atmosphere at the height of the fire. At stoneware and porcelain temperatures (~2400°F, ~1300°C) these salts readily break down, releasing sodium vapor into the kiln. At such temperatures, the sodium vapor will combine with the silica and alumina present in the clay body to form a glaze. In fact, the sodium combines with all forms of clay - including the kiln's interior!

I live in an urban neighborhood, so I must be mindful of the imposition my kilns might put upon my neighbors. Originally, I chose to "salt" my kiln with sodium carbonate (washing soda) and sodium bicarbonate (baking soda) because burning table salt (sodium chloride) releases unpleasant chlorine compounds. However, I have since grown to love the aesthetics of soda glazing as much as salt glazing and wood firing (if not even more!). Soda glazed pots have an aesthetic quality different from salt glazed pots, including a higher potential for flashing (a color response of the clay permanently recording the path of the flame over and around the pot) which is more typical in wood-fired kilns than salt.

I designed m y soda kiln as a cross-draft type, in order to take best advantage of the directional quality of the soda glazing and flashing. I built in several salt ports. But, I now spray the soda solution primarily through the front port in the firebox and occasionally through the burner ports (both visible in the photo to the right). I built the kiln in the summer of 2000. The bricks were gleaned from the arch of a 100-yard long car kiln being demolished in Milledgeville, Georgia. Several weekend excursions in my truck, along with some hours of cleaning off old mortar rendered enough bricks (free of charge!) to build the kiln and stack. See also my "Notes on Firing" on the Glazes & Clay Bodies page. The questions remain, "Did I make the right decision constructing it almost entirely of hard brick? Was the trade-off of free brick versus higher gas bills worth it?" After about 20 firings, I have no regrets. However, if I were purchasing bricks, I would definitely go with a hard brick interior and and IFB exterior.

Plans are to build another soda kiln at the school where I teach (Marist School) within the next couple years. The students have responded amazingly to soda fired work. Callanwolde Fine Arts Center also has a soda kiln project under way.

If you are interested in a soda workshop or in building a soda kiln, contact me at bbuckner@sodaglaze.com.

-BB