I remember being at a science conference and they were giving away rock
samples - we had a discussion on clay and firings and I asked what would
happen to some of the rocks in a kiln - the answer was some of them could
explode - always check -
There are some safety issues, so I encourage students to check with me
before trying something new. If you are not sure if something is safe,
check with a science teacher or a local potter about the fumes that will
come out of the kiln when you fire something. Ordinary smoke is okay if
your kiln is well vented. Otherwise, expect a call from the fire department
when your smoke alarm goes off. Table salt is not okay for classroom firing.
Salt contains soda which is a great glaze ingredient, and potters have long
used salt by throwing it in their kilns when the kiln is 2,300 F. Potters
realize that salt also gives off toxic chlorine gas, so they take
precautions. Potters also know that the soda vapor tends to melt the kiln
surfaces as well as the pots. Salt kilns are dedicated to this use and they
are fueled with wood, gas, or oil - never with electric elements.
I am writing a lesson about stuff that melts. It combines science and art.
When it is posted, I will send another note.