In the top center of the main panel (upper left in this detail), the blast furnace has been tapped and the molten metal rushes out into an open sand trough and is diverted to a metal dam that separates the slag floating on the top from the pure molten iron underneath. The flowing molten iron casts an orange light on the lower section of the furnace. The furnace has not been altered in design or scale, nor are the billows of smoke and color exaggerated. Observe the similarity to a volcano.

Electric motor-driven spindle machines (at right) ream the valve ports in the engine block. The valve ports are part of the intake and exhaust system of the engine. The prominence given the multiple spindles in the mural is not due to their function but to their form. Unlike all other representations of machines on the north and south wall automotive panels, Rivera disregarded the actual scale of the spindle machines and magnified them to tower over the figures and dominate the panel. Two reasons may have contributed to this deviation—a needed for compositional balance and Rivera's desire to point out the analogy between these machines and Pre-Columbian sculpture. Two rows of multiple spindles divide the panel and provide dominant compositional elements, echoing the symmetrical division of the upper two registers on both the north and south walls. The machines can also be seen as monolithic guardian images flanking the entrance to the conveyors, which extend into deep space and give the impression of forming an avenue, with the blast furnace at the end.

---