Modern kilns are thermally insulated chambers that heat their contents to thousands of degrees on a timer. The kilns range in size from compact and discrete to as large as a walk-in closet. Most kilns are owned by schools and professional ceramics studios; however, anyone with a backyard and a few tools can easily and inexpensively make a kiln.
Dig a hole in the ground. The size of the hole will depend on the amount of pottery you regularly plan to fire. It should be at least 2 feet deep, but may be as deep as 3 or 4 feet, as necessary.
Layer the bottom of the kiln with shredded paper, charcoal and wood chips. The depth of this layer depends on the depth of the kiln and the size of the pottery. There should be enough room left in the kiln for the pottery. Put saw dust on top.
Place the pottery on top of the layer of sawdust.
Place peat moss and sawdust in and around the pots.
Top the pottery off with a layer of straw that has been soaked in salt water or sea water, then dried.
Add cow-pies (dried cow poop) to the top layer, then more sawdust.
Put a layer of kindling and then larger logs for burning on top of the pile. This mound should be sticking above the ground like a campfire.
Light the fire and let it burn bright for a couple hours.
Cover the fire pit with a metal lid or a piece of sheet metal. This lid should be propped up on bricks just above the fire, to allow oxygen into the kiln.
Allow the kiln to burn until it extinguishes (at least one day). Give the kiln and pottery another day or two to cool before removing the pottery.
You may want to reinforce the sides of the kiln with sheet metal. This will need to be maintained after every firing because the prolonged exposure to heat will cause the sheet metal to warp.
Don't leave the kiln unattended while burning. Clear the entire area around the kiln of grass and sticks. Leave the ground around the kiln bare to prevent extra fires. Check with your municipal fire codes before lighting a fire in your back yard.