Abstract: A process for manufacturing a vitreous slag including rotating a cone about a vertical cone axis, the cone including an external shell having a lateral surface; cooling the lateral surface of the external shell; pouring molten slag onto the lateral surface of the cone to form a film of slag by gravity, which is solidified as it is entrained in rotation by the cone about the cone axis; and detaching pieces of the film from the lateral surface and removing solidified slag in the form of the pieces after the film has been entrained through between 0.6 and 0.9 revolutions of the cone, the molten slag being poured onto the lateral surface in a pouring zone and spreads to form a film over substantially the entire length of the lateral surface, preferably over between 75% and 95% of the length of the lateral surface.