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Vermiculite is a mineral that is mined throughout the world.  Often sold as potting soil in garden shops, its industrial uses range from insulation to absorbent packaging to filtration to fireproofing.  It's even used for fireproofing doors and safes and for fading and aging  "stonewashed" denim jeans. 


From a glass perspective, vermiculite's refractory properties make it ideal for use in the glass studio.  Bead makers often plunge hot beads into loose vermiculite as a way to slow down the rate of temperature decrease.  Loose vermiculite can also be added to molds to increase strength and reduce the likelihood of thermal shock.


Vermiculite can also be pressed and glued into board form (not unlike pressed wood or particle board).  Vermiculite boards, which are most frequently marketed by a Danish company named Skamol, can be used as dam material or as a kiln shelf. 


From a health perspective, vermiculite is considered a nuisance dust.  Small particles can irritate the eyes or lungs, but careful handling (and a dust mask and safety glasses) will eliminate this concern.  On some occasions in the past vermiculite deposits in mines have been contaminated by adjacent asbestos deposits, but this is relatively rare.  Most vermiculite mines are tested for asbestos and in most cases vermiculite is no more risky than any other nuisance dust.



Copyright 2005 Brad Walker.  All rights reserved.

This article is one of a series on refractory materials for the kiln worker. Future tips will deal with vermiculite board and with other refractory materials such as mica, plaster, and various metals.

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