Metal trash cans work well as raku kilns for firing small batches of ceramic greenware. They contain the fire neatly, and have less risk of fire spreading than open pit fires. You can also leave ceramic-ware in a can kiln to cool down, so you are also less exposed to the fire. Trash can kilns also can be run on things that are readily available, such as sawdust and newspaper, and don't need any special equipment.
Things You'll Need
Metal trash can with lid
Drill holes in your trash can to allow ventilation. Drill a ring of holes around the top of the can that are spaced 5 to 6 inches apart, and another ring around the bottom that are spaced 3 to 4 inches apart. Drill a few scattered holes around the middle of the can to make sure that all the embers get enough ventilation. You don't need a lot of holes because raku firing is a reduction process where the clay pieces themselves aren't exposed to oxygen, but you need enough to keep the embers from dying out in the firing process.
Place the trash can in a secure location, without anything near it that might catch fire. The best way to do this is to either dig a small pit that the trash can can then be placed in, or to lay down a bed of cinderblocks below the trash can.
Cover the bottom of the trash can with 2 to 4 inches of newspaper and sawdust. Already fired bisque-ware doesn't need as deep a base as unfired greenware because it won't shrink as much in the firing process.
Put one layer of leather-hard pots that are ready to fire in the bottom of the can on top of the sawdust. All clay pieces should be at least 1 inch from the side of the can to ensure that they get properly fired. If there isn't enough room for all your pieces, you can always stack them in the second layer of the kiln.
Fill sawdust in around and above the clay pieces until you can't see or feel them any more. You should have about 1 to 2 inches of sawdust between each layer of clay pieces.
Fill the kiln by stacking alternating layers of sawdust and clay pieces until the can is almost full. There should be at least 3 inches between the top of the last layer of clay pieces and the top of the trash can.
Fill the top layer of the trash can with crumpled newspaper and sawdust.
Light the layers of crumpled newspaper on the top and the bottom of the trash can, and leave the lid slightly ajar until the fire is going and can be supported on the ventilation holes alone.
Cover the trash can when the fire is well-lit and there are plenty of hot embers, and leave it to burn all day or overnight. When the fire burns out and everything has cooled down, you can reach into the trash can kiln with a pair of thick work gloves and pull your pieces out.
Check your local fire ordinances before you start a large fire in your backyard, as not all municipalities allow open fires outside of grills.
After you have emptied the kiln, pour water over any remaining embers to make sure that nothing is still lit.
If you fill you trash can kiln with newspaper instead of sawdust, you may end up with ink marks burned onto your clay pieces. The best way to avoid this is to use sawdust around all your clay pieces.