Firing Rocks in the Kiln
One common glass project involves firing glass over rocks in the
kiln to simulate the flow of a stream over a bed of stones.
This is actually a fairly straightforward slump project, but there
are a few tricks to get the right effect.
Start with the rocks. You can purchase stones in a local
craft shop or even pick them up along a creek, but in either case
you'll have to take steps to ensure that the rocks you choose are
capable of withstanding the heat of the kiln. The problem is
that some stones contain moisture and will crack or even explode in
the kiln; consequently, you'll need to test to make sure your rocks
The easiest way to do this is to pre-fire the rocks in your kiln.
Place them in a container (a terra cotta flower pot base will work,
as will an old slump mold) and cover the container lightly with a
few scraps of fiber paper. Place the paper loosely over the
rocks, so that some air can flow and the rocks won't be totally
protected from the heat of the kiln.
Now fire your kiln. Use a standard slumping schedule, the
one you'd use for glass that's around 1/4" (6cm) thick. Try
firing at 300 degrees F per hour (167C) until the kiln reaches 1250F
(676C), soak for twenty minutes, then turn the kiln off and let the
If they survive the firing intact, then you're ready for the next
step. If any rocks crack, then remove those and use the good
Click here for the next step in the process -- firing the glass.
Copyright 2006 Brad Walker.
All rights reserved.