The ironmaking industry had an important role in America’s
technological and industrial development. It was one of the
country’s earliest industries. There are many remnants of iron
furnaces scattered around the country; most are just languishing
stonework, but a few have been preserved as examples of a
The mechanics of the furnace: iron ore into pig
In past issues two of the most interesting of the
remaining charcoal iron furnaces in the country were discussed:
Hopewell Furnace in Pennsylvania and the
Tannehill Ironworks in Alabama. Ironworks were an
integral part of the foundation that allowed for America’s
industrial revolution. A third Ironworks, Cornwall Iron Furnace,
located about 30 miles east of Harrisburg, Pennsylvania, is the
only surviving intact charcoal cold-blast iron furnace in the
Cold-blast technology (the air was not preheated before being
blown into the furnace) was prevalent until the 1840s, when the
hot-blast iron furnace became necessary to burn anthracite coal.
Cornwall Iron Furnace is probably the best single locations in
the country to view an iron furnace in terms of the operational
aspects of the cold-blast iron making process. It still has, not
only the intact furnace, but the entire furnace house,
supporting buildings, and ironmaster’s and laborers’ residences.
One gets a true feeling for what the community must have looked
like. This was a charcoal iron furnace plantation, a
self-sustaining community. The historical site is five acres in
size. The actual plantation was closer to 10,000 acres, with its
own agricultural fields and pastures and woodlands needed to
produce charcoal. Perhaps 5,000 - 6,000 of those acres would be
necessary to produce charcoal on a sustained basis (charcoal
production at a nearby iron plantation was discussed in the Fall
The blast furnace building where
iron ore, limestone, and charcoal became pig iron.
Originally separate buildings were clustered around the
furnace stack. In the mid-nineteenth century the furnace
was remodeled into this larger building with its elegant
fašade and Gothic Revival detail.
Stone buttresses built to support the
railway that transported ore from the mine to the site.
The furnace operated from 1742 to 1883 and, like other furnaces
of its time, was located near four key requirements for iron
production: iron ore, woodlands for charcoal production,
limestone (a flux or chemical agent that cause the slag to
accumulate impurities), and water power. Peter Grubb began
mining in the area in the 1732 and established the furnace in
1742, naming it after his birthplace in England. The British
Parliament discouraged iron production in the colonies, but iron
output grew and by the time of the American Revolution the iron
industry in the colonies exceeded that of Great Britain.
With 80 furnaces in nine
of the colonies, America accounted for about one-seventh of the
world’s iron output. Pennsylvania, with about 20 furnaces, had
the largest number of any colony. The American Revolution likely
would not have been successful without the locally-produced
ordnance and ammunition.
Near Cornwall, visible from the road, are the Cornwall Ore
Banks. This deposit
of magnificently rich magnetite ore remained one of the most
valuable iron ore bodies in the country until the discovery of
the Lake Superior deposits. This is what caused Peter Grubb to
invest in an iron furnace. When the mine was worked, it was the
largest open-pit iron mine in the eastern United States.
After the furnace closed Bethlehem Steel Company
purchased the pit mine and operated it until 1973 when flooding
caused by Hurricane Agnes closed it. Today it looks more like a
charming lake surrounded by rock cliffs. The pit is about 500
The buildings have many
interesting artistic features,
like this window on
The normal beginning point of the furnace tour is the visitor’s
center, located in what was the charcoal barn.
This barn has four large rooms or bays that were used to
store the charcoal, produced in the surrounding forests by
colliers and transported there by teamsters. The barn was filled
using ground level doors. The barn held enough charcoal for 100
days of production and, when the supply grew beyond the ground
openings, roof ladders were used to add charcoal via roof doors.
All the other bays opened to the second bay that has access to
the furnace by the connecting shed. The visitor’s center
contains sets of exhibits centered on the furnace history,
charcoal production, iron ore mining, and the ironmaking
process. Some of the products produced at the furnace are on
display. The furnace tour stars with an orientation video in the
first charcoal bay before entering the furnace building via the
Much of the equipment is still at the furnace,
the carts used to haul iron ore and charcoal.
The furnace building is only accessible by a guided tour that
starts on the charging floor.
The furnace building is actually several connected
buildings assembled around the furnace stack. The building was
remodeled in the mid-nineteenth century in the Gothic Revival
style. The charging floor is where fillers, under direction of
the founder, dumped buggy loads of iron ore, limestone, and
charcoal into the mouth of the furnace. The visitor gains a good
overview of the 32 foot furnace from the charging room,
including its general shape and construction. Various equipment
was used to feed the furnace is still there, including the
buggies. The larger
ones were for charcoal and the smaller ones for the heavier iron
One of the products of the furnace was cannons.
The tour moves on to the Wheel Room, containing the blast
equipment. This is suspected to be the sole remaining example of
this type of equipment that is still intact. The room is
dominated by the “Great Wheel,” 24-feet in diameter and weights
four tons. It powers the wood and leather bellows that pumped
air into the furnace to create greater heat. The wheel is
actually turns during the tour.
Next comes the Engine Room, containing a working steam
engine that powered the blast equipment.
It was installed about
1841 and is still capable of powering the wheel.
At the bottom of the furnace is the Casting Room (also called
the cast house or casting floor). This is where the molten iron
flowed out of the furnace and was molded into pig iron or cast
iron products, such as stove
plates, pans, and cannon
balls. This is the opposite view of the furnace as from
the charging room and the visitor get a feeling for the massive
structure of the furnace. There is one of 42 cannons cast for
Revolutionary War naval frigates on display.
Near the building is a roasting oven used to roast the iron ore
to remove sulphur, which would cause problems in the smelting
process. Layers of charcoal and iron ore were loosely packed to
allow for upward movement of the air. Also nearby are large
stone coal bins used to store coal that heated the workers
houses and the ironmaster’s mansion.
Other stone buildings
are the blacksmith shop, wagon shop, and abattoir (smokehouse
and butcher shop). There are other related sites, not owned by
the historic site, that
were part of the original iron plantation. While they cannot be
visited, they are easily observed and are near the furnace.
These include a stable, the manager’s house and mine office, the
open pit mine (now flooded), the miners village, an office
building, and the ironmaster’s mansion. You will probably drive
through the miners village when you enter town. The buildings
are stone; all constructed alike, and form a quaint picturesque
“company town” image.
The casting house at the bottom of the
where the iron was discharged. Notice the pig iron in the foreground
Profitability of the furnace decreased after the Civil War when
new steel mills opened in cities like Pittsburg and Bethlehem.
After losing money for a decade the furnace closed in 1883. The
furnace property was donated to the Commonwealth of Pennsylvania
in 1932 and is operated today as a state historical site. It is
a national historic mechanical engineering landmark. The report
on the landmark notes “that Cornwall was spared the depredations
of weather and salvage is nothing less than a miracle of
industrial archeology” and that it survives “as the only
18th/19th-century American blast furnace with its original
Author and Photographer:
Tom Straka is a forestry professor at Clemson University in
South Carolina and has a keen interest in roadside history. Doug
Page is a retired Bureau of Land Management forester and
resides in Cedar City, Utah.
For more information:
Cornwall Iron Furnace:
ExplorePAhistory.com-Cornwall Furnace Historical Marker:
Cornwall Iron Furnace – National Historic Mechanical Engineering
Cornwall Iron Furnace – Pennsylvania Trail of History Guide by
A Blast from the Past: Cornwall Iron Furnace by Sharon Hernes
Ads fund American Roads so please consider them for your needed
If you enjoy the articles we offer, donations
are always welcome.