Nassawango Iron Furnace

Library of Congress, Historic American
Engineering Record

The nassawango iron furnace was constructed near the site of a large quantity of swamp bog ore located a few miles west of Snow Hill, Maryland. The ore was discovered near the end of the eighteenth century and, shortly thereafter, the Maryland Iron Company was incorporated. By 1832, a cold blast furnace had been constructed, as had a small town surrounding the structure. The furnace was powered by water, fueled by charcoal and was in operation about 40 weeks of the year. The smelting operation was shut down during the winter months. Nassawango annually produced about 700 tons of pig iron.

Three bodies of water located in the area played major roles in both the manufacturing and transportation of the pig iron; two of them, the Nassawango Creek and the Pocomoke River, constituted a natural waterway to the Chesapeake Bay. The third, a man-made canal, served a dual purpose--it provided the energy necessary to operate the furnace and formed a waterway that connected the furnace with the Nassawango Creek.

The furnace was charged twice daily with appropriate amounts of bog ore, shells, and charcoal. The temperature in the furnace was raised to 3000° F and the charge slowly liquefied. Slag, a waste product, was poured from the slag tap hole. The molten iron flowed from the tap hole under the hearth and filled molds cut into a sand floor. The iron was called pig iron because the shape of the molds resembled a sow nursing piglets.

The “pigs” were about two feet in length and weighed 25 pounds. Once they hardened and cooled, they were loaded onto barges for the journey down the canal to the Nassawango Creek. At the junction of the Creek and the canal, the pigs were transferred to schooners for the trip down the Pocomoke River and into the Chesapeake Bay. Once in the bay, the cargo was taken to one of three large ports: Baltimore, Philadelphia, or New York City. Cast iron water pipes were also manufactured on the Nassawango site and were sold to the city of Philadelphia.

In the mid-1830s a stove and circulating pipes were placed over the top of the stack. The air pumped in by the bellows was preheated and the furnace became hot blast in operation. While this innovation did not serve to increase production of pig iron, it did improve the efficiency of the furnace. Iron smelting at Nassawango ceased about 1850. Although in operation less than 20 years, the furnace provided much needed pig iron to three important manufacturing ports.

American Society of Mechanical Engineers, DelMarVa Group. Nassawango Iron Furnace, A National Historic Mechanical Engineering Landmark. New York, 1991.

Chard, Jack. Making Iron and Steel, The Historic Processes 1700-1900. New Jersey: North Jersey Highlands Historical Society, 1995.

Rolando, Victor R. 200 Years of Soot and Sweat: The History and Archaeology of Vermont’s Iron, Charcoal and Lime Industries. Vermont: Vermont Archaeological Society, 1992.

“Nassawango Iron Furnace.” ASME, http://www.asme.org/history/roster/H159.html. Choose "Search the Database” under Explore Maryland’s National Register Properties.