The casting arch provided access to the furnace hearth area and was the largest of the four arches in the furnace structure. Through this opening, molten iron flowed into sand molds to form iron pigs, the furnace’s final product, and slag was also removed. When the furnace operated, the area in front of the arch was enclosed within a large casting shed, whose low stone foundation walls remain around the furnace stack. Old photographs show that the casting shed had two large doors, one in front for removing iron and one on the side toward the Blackberry River for removing slag. In the hearth area, molten iron was removed from the furnace, and at the bottom of the furnace stack a small cylindrical chamber called the crucible collected the molten iron beneath a layer of glasslike slag. Openings in the crucible were plugged with clay until the furnace was tapped, first to drain the slag and then to release the iron, which was directed into molds in the sand floor of the casting shed and hardened into ingots called pigs. A water jacket around the hearth helped lengthen the life of the refractory bricks and keep the furnace in service for longer periods.