Stol™

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.