Of the three methods of firing clay at home, this one is the most traditional. People have been using pit fires to fire clay for a long time. This would be a great project to try as part of your homeschooling history curriculum.
How to Pit Fire Clay at Home
The first thing you need is a pit! Dig a hole big enough to hold your clay pots and lots of fuel. If the soil is damp you may want to line your pit with cardboard.
Fill the bottom of the pit with a layer of sawdust - you will need several inches.
Add your pots. Put them in different directions to get different effects. You can also add copper and salt around your pots for flashes of colours to be produced in the finished pieces. Some people make little parcels of their pots - adding copper and salt then wrapping in newspaper with copper wire - but this technique works best with pre-fired pottery.
For best results make sure your pots are totally dry before trying to fire them.
Build up layers of sawdust, paper and dry wood around your pots. You want to add enough material to allow the fire to burn for about an hour or so - but sawdust does burn quite slowly. You can also add dung as it burns hotter and longer than wood, but it was not used in prehistoric times. You may need to experiment with different types of wood.
There is more information and some great pictures of this at Maui Potter.
Light your fire from the top and allow to burn. Allow your pots to cool the same amount or longer as the heating process.
Leave your fire to smoulder and cool. You can cover the pit with a piece of metal to help the process.
When everything is cool, you can dig up the fired bisque. Clean it with a wire brush and water, then rub with a clear wax such as beeswax or natural shoe polish. The finished piece will be porous so cannot be used for liquids.
If you try out this method in your homeschooling, I would love to hear how it went.
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