Making Iron

Ore, charcoal, and gabbro rock used as flux were hauled to this site, where a drying fire was started in the furnace and, within a day or two, water wheels and bellows set the blast in motion to burn uninterrupted for weeks. Workers returned from the forest, bogs, and the gabbro quarry at Nahant to toil around the clock, feeding measured layers of ingredients into the charging hole. The 340 cubic foot furnace interior held three tons of ore, 265 bushels of charcoal, and two tons of gabbro rock as a fluxing agent. After three days of intense heat from the continuous blast, the ore and gabbro were reduced to liquid and the filled crucible was emptied of its molten contents, while the furnace was repeatedly tapped as layered charging continued day and night. Bog iron ore, the mineral limonite, was dug from stagnant ponds and swamps, and up to 1000 tons were delivered to the furnace each year. Gabbro, an innovative local discovery that aided smelting, replaced the limestone traditionally used in the 17th century ironworks of England. Charcoal, used in great quantities as furnace fuel, was produced by woodcutters and skilled colliers in nearby forests, and the weight and flow of water in the overshot wooden wheel generated the constant horsepower needed to operate the huge bellows that sustained the continuous blast.

Saugus, Massachusetts · United States