Perlite is a Slag-Holding compound is added as a slag coagulant in continues induction furnace and in molten metal pouring ladles, prior to pouring in the mould. It may be added either to the surface of the bath after the ladles is filled or to the bottom of the ladle after a heel of molten metal has been poured. 

The accumulation of Perlite attracts all individual slag particles in the metal, cleans the metal by coagulating impurities, floating them up to the slag layer and also re-entry of the impurities into the metal.