I thought I would share some information today about how I fire pottery. I have done a lot of experimenting in firing processes and have had success with many of them but this is how I am currently doing it and I think is probably very close to how the prehistoric residents of my area did it. This method will work on most native clays to fire in an oxidizing atmosphere. Firing is best accomplished in the early morning when there is less wind and using very dry wood.
Step One: Preheat Pottery and Make Coals
You will need a good bed of coals before we start firing the pottery so use wood that will create coals, I usually choose good hard, dry mesquite wood about the thickness of my wrist, if you use larger logs you may be here all day waiting for them to burn into coals. It is important to heat your pots up gently, rapid heating can cause cracks, I heat mine up around my initial fire to allow them to start heating up and to drive off any residual moisture that may be in the clay.
Step Two: Arrange Pottery Over Coals
Once I have a good bed of hot coals created, I spread them out into a consistent layer and place rocks on the coals on which to prop up the pots. A word of caution, be aware that certain types of rocks can pop in the fire and damage your pottery, specifically avoid limestone and any stone that might have moisture in it. Once your stones are placed, position your pots on them. The goal here is to allow good air circulation, under and around your vessels. There are three methods of heat transfer, convection (hot air), conduction (through solid objects) and radiation (rays), the number one method heating up your pottery in an open firing in convection so the more you can allow air to circulate the more efficient your firing will be (and the less sooty your pottery will turn out). Try to pack your pottery close with a minimal of touching other vessels, if vessels must touch or stack, make sure that air will be able to circulate freely otherwise you may get dark, sooty spots where your pottery touched or inside vessels stacked atop others. Notice the photo above, the red bowl is stacked on top of three others but touches them only in a small spot and it is open underneath all the way down to the coals, remember that hot air rises, make allowances for that and allow it to flow unrestricted. Once you get your pots situated, take a few minutes before you move to the next step, this will give your pottery a chance to heat up more slowly before the conflagration finishes the processes.
Step Three: Stack and Light Firewood
Now arrange the firewood over your pottery being careful not to knock any pots out of position while doing it. You will want to use mostly light fuel that will burn quickly, completely and hot, the goal with this fire is to not leave any coals because coals will leave black spots on your pottery while white ash leaves nicely oxidized pottery. Notice in the photo above that I have stacked the fuel very loosely, do not stack your fuel tightly because this will restrict the fire’s access to oxygen, you want a very fast and hot fire, this is encouraged by using small, dry fuel and allowing it plenty of oxygen. My sticks here probably average the thickness of my thumb, some are thicker but many are smaller, remember, we want this fuel to quickly turn into white ash, not black coals. The wood may begin to burn before you are done arranging it, lit by the hot coals on the bottom, make sure your wood is ready before you start so you can get this done quickly before it lights.
Step Four: Let It Burn
Up to this point you have worked hard collecting firewood, starting the fire, arranging the pots and the fuel, now you can take a break because there isn’t anything you can do to effect the outcome now. I usually pace around the fire like a nervous cat and listen for pot breaks, not that it helps, but it is the natural expression of the anxiety associated with this trial by fire. The key to avoiding broken pots during firing is 1) careful and thorough preheating, 2) never fire when windy, 3) avoid leaving air bubbles in your clay.
Step Four: Inspect the Results and Let Cool
As the fire starts to die down I will flick away any remaining smoldering logs that may leave black smudges. Just as I was careful to heat my pottery up slowly, I must avoid the compulsion to snatch it out of the fire too soon because it must cool down slowly. The pottery is so hot at this stage that touching it with anything that can burn like a stick, glove or towel can leave black, carbon deposits on the pot, or worse, melted plastic stuck on your pot. Once it has cooled down a little, you can start carefully fishing them out one by one. You will notice that your pottery has changed color in the firing, reds usually come out a dark chocolate brown, but don’t be disappointed, as it cools the dark brown will turn back to red, I have always marveled at this, it usually seems to grow redder and redder for an hour or so after the firing.
Step Five: Examine Your Pottery
Once your pottery is cool enough to handle you can examine it to see how it came out, then load it up to take home. Make sure you put your fire out completely before leaving.
Use the comment form below to tell me how your process differs from mine or to ask questions if any of this is unclear.