Cordierite and Mullite
This is part of a series of tips on refractory
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Cordierite and mullite are naturally
occurring minerals that are commonly used to make kiln shelves and
related kiln furniture items. Of the two, cordierite is the
most common; mullite is rarely found in nature and is usually made
synthetically and sold as a white powder.
Most often, kiln shelves are made from a
mixture of cordierite and mullite powder, which is mixed with clay
and other ceramic materials, shaped, then heated to form kiln
shelves. Mullite shelves are sturdy, rigid, and long lasting,
but they can break if dropped and may crack or cause air bubbles if
heated when not dried thoroughly.
Really large mullite shelves are generally
not manufactured because they're very heavy and they also tend to
warp as the size increases. If you break your shelves, don't discard
them; instead, use a tile saw to cut them into strips to use as dam
Interesting tidbit: In its natural
state cordierite appears bluish when viewed from one direction and yellowish
gray when viewed from the other. The stone is sometimes called
which is a Greek
word, meaning "two colored rock." This same Greek work is also the root of "dichroic."
Copyright 2005 Brad Walker.
All rights reserved.
This list compiled from numerous
sources, including the Warm Glass board, and manufacturer's materials.