How Marbles are Made

This video from How It’s Made shows the marble-making process. Sand, soda lime, and crushed glass are fed into a large tank where the mixture is heated to 2200 F for 16 hours until completely melted. Next, molten colored glass is added. Then, the still-molten glass is released from the flow tank as “slugs” that flow into spinning cast iron grooves that cool them and perfect their spherical shape.