Ceramic Containers
As part of the continued experimentation and development of my personal work, I felt there was one aspect of pit firing that I had not tried—saggar firing. Saggars are ceramic containers made of a high temperature clay traditionally used to protect more delicate ceramics in the kiln.
I used saggars, in this case, as mini pit firings with combustible materials packed in the same manner as pit firing. However, the pots were fired in a traditional up-draft kiln using propane gas as a fuel rather than a bonfire in an open earthen pit.
Creating Saggars
The work began by buying a clay more resistant to thermal shock than the clay the pots were made from. The new clay was used to build the saggars by hand. I make my saggars from a Raku clay body on the potter's wheel or with slabs of clay and bisque at a high temperature. When saggars are leather hard, I cut a number of random holes on the bottom and sides of the saggars. I have used terra-cotta chimney flues as saggars, but they are expensive and only last for about 3 firings. Fire bricks stacked to create a saggar have not served me well.
Subsequent firings with saggars showed improvement in the desired results and reduced the fatality rate of pots from thermal shock, as compared to pots fired in earthen pits used earlier. The saggar firings have reduced the number of firing fatalities and have consistent, rather dramatic displays of color rarely seen in pit firings.
Saggar Firing
The primary fuel is sawdust and hard woods. I use an assortment of combustible materials, paper, straw, dry weeds, grass, as well as copper carbonate, iron and copper sulfates (must be handled with care), Spanish red iron oxide, and small amounts of moist sea salt. I use a pyrometer to measure the temperature and I do not use cones. I begin the firing as if I were firing bisque by starting with a soft flame for the first hour, gradually turning up the burner every hour until kiln termperature reaches 800 degrees Fahrenheit. At this state of the firing, it is safe to turn up the burners more frequently to attempt to reach 1,500 degrees Fahrenheit within four to eight hours. The next step is to shut the burners off, plug all openings, and do not disturb for eighteen to twenty hours.