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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 will work.


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 stones cool.


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 ones instead.


Click here for the next step in the process -- firing the glass. 


Copyright 2006 Brad Walker.  All rights reserved.

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Copyright 2005-2006 by M. Bradley Walker.  All rights reserved.

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