posted 6 years ago
There are various grades of kiln, with pit firing being near the base. What you would do with this is put a mix of small wood and pots in, light the fire, and mostly cover it so it doesn't flame up vigorously but keeps burning. Uncover the next day and see what you have. This can fire pottery hard enough to use gently, though it will not be waterproof. Some pieces will probably not be fired hard enough to keep from melting in water, and some will most likely break from thermal shock. It gets better with practice. This is one of the earliest kinds of firing practiced in primitive cultures.
A more advanced kiln which can fire much hotter and make harder pots requires a fire with a good air supply underneath the ware chamber where the pots sit. For this, dig another hole next to the first, about a foot away, and large enough to stand and feed the fire without scorching your shins. Dig a hole, maybe head-sized, between the bottoms of the holes, put your pots in the first pit along with enough things to fill it to the top leaving plenty of airflow space. Build a fire in the connecting hole and slowly push it farther into the first pit until it drafts up through the pots. As the pot chamber gets hotter, it will draw more strongly. You will need to keep the fire going steadily for several hours until the interior of the pot chamber, or "ware chamber" as it is properly called, is glowing orange inside.
There is much more detail involved, but that is the essence.