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January 14, 2011

STOL® is the trade name for a naturally occurring siliceous volcanic rock called  perlite.

   The distinguishing feature of STOL® is that when heated above a suitable point in

its softening range it expands up to twenty times its  original  volume.  In  high 

temperature  applications,  such as those encountered  in the iron-and-steel and foundry

industries, the expansion of STOL® results  in  particles with large surface areas.  This

expansion is also  accompanied  by  a  small  cooling  action.  These effects combine

to coagulate slag, the unwanted by-product of metal smelting, and thereby form a

viscous, toffee-like mass that can be effectively removed from the molten metal 

interface. An added advantage of perlite in this application is that no objectionable

smoke or noxious fumes are produced.