Appalachian Center for Crafts - Clay Studio

Vince Pitelka, 2006

Hoggama Firing - General Information

The following information will prove useful for anyone preparing to help fire our "hoggama," a hybrid ground-hog/anagama wood kiln with approximately 200 cubic feet of stacking space.  You can see images of the kiln and find more information about it on the wood kiln page.  

Air Port Management - After moving fire inside kiln, start off with upper air ports closed off, and mid-level ports half closed.  Regulate air ports in order to maintain good draft and a good fire, but always avoid letting excessive cold air into kiln.  As long as the temperature is climbing, and as long as you can see good flow in the smoke exiting the stack, there is ample air supply.  The upper air ports are pretty unnecessary, since air is always drawn in around the stoke door.  Keep the bottom air ports (the mouse holes) at least partially open by raking the accumulated coals and ashes out from under the coal bed at least every few hours.   

Kiln Log - please be responsible about recording information.  For each entry, note the date, the time in AM or PM, your initials, pyrometer temperature, condition of cones, and frequency of stoking, plus any pertinent comments.  You do not have to log every time you stoke, but make sure you log at least once per hour, more often whenever you change frequency of stoking or notice some change in the performance of the kiln. 

Cone Packs - whenever possible there should be two cone packs in each location.  The front cone pack in each location faces right and contains cones 010, 04, 1, 5, and 7.  The rear cone pack in each location faces left and contains cones 9, 10, 11, 12, 13, and 14.  Make the cone packs very stout and stable, and poke lots of holes in the clay with a needle tool.  

Frequency of Stoking - As you might expect, the frequency of stoking increases through the firing.  Initially, there will be no flames in the stack or at the crown ports, so we will simply maintain a fire, first in the temporary fireplace in front of the kiln, and then in the firebox, building up the heat very slowly.  Once we reach cone 010 we start breathing-cycle stoking, waiting until the smoke at the stack and crown ports subsides for a minute or so before stoking again.  At that stage you will probably be stoking about every fifteen to twenty minutes.  In the latter half of the firing you can watch the flames in the passive damper port on the front of the stack.  Through this stage of the firing we will need to increase the frequency of stoking, and when going for maximum temperature climb we will likely stoke every five minutes.  If you are having trouble getting the kiln to climb, increase the frequency of stoking.  However, with dry hardwood and pine, it is very unlikely that we will have any trouble getting the kiln to climb.  Be especially cautious once the kiln gets up to high-fire temperatures, because we want to maintain a very slow steady climb in the range from cone 9 to cone 11 or 12 through the last day and a half of the firing.  

Backstoking - We usually begin backstoking early in the evening of the second day when the pyrometer reads 1800 to 1900F, and regulate the frequency of backstoking to bring up the temperature in the rear.  From that point onwards, backstoking is regulated to keep the temperature as even as possible front to back.  When increasing backstoking, do so more frequently but with only a few sticks each time.  The objective is to avoid building up a coal bed in the back, because it serves no purpose and can damage adjacent wares. 

What Wood to Use When - Initially we will start the “campfire” in front of the kiln with hardwood edge-trimmings and smaller planks.  Use up all the scrap wood you can find at this time, including whatever is laying on the ground at the base of all the woodpiles.  When we move the fire inside the kiln on Thursday morning we will continue to use small wood, gradually shifting over to small branches and split firewood, and by Thursday around noon we should be burning split firewood exclusively.   As much as possible, we should burn a mix of hardwood and pine.  You will be able to tell the pine from the hardwood by the bark or by the smell of the wood.  The pine will release a big burst of energy and ash, but burns quickly.