Glass flowing down the Forehearth Channel from the Primary Furnace is always a single color. To make a multicolored glass, secondary colors are melted in smaller, separate furnaces (Day Tanks) and hand-ladled into the stream at the Ladling Bay.
The two (or more) glasses are stirred together by hand in the Stirring Bay just before reaching the Forming Rolls. The Furnace Operator uses a special rod to stir the glasses. This stirring technique creates the swirls in a multicolored glass.