Cornwall Iron Furnace | |
![]() Main building at Cornwall Iron Furnace | |
Location | Rexmont Rd. and Boyd St., Cornwall, Pennsylvania |
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Coordinates | 40°16′14″N76°24′22″W / 40.27056°N 76.40611°W |
Area | 175 acres (71 ha) |
Built | 1742 shutdown 1883 | ,
Architect | Peter Grubb |
NRHP reference No. | 66000671 [1] |
Significant dates | |
Added to NRHP | November 13, 1966 |
Designated NHLD | November 3, 1966 [2] |
Designated PHMC | August 1, 1948 and June 1, 2005 [3] |
Cornwall Iron Furnace is a designated National Historic Landmark that is administered by the Pennsylvania Historical and Museum Commission in Cornwall, Lebanon County, Pennsylvania in the United States. The furnace was a leading Pennsylvania iron producer from 1742 until it was shut down in 1883. The furnaces, support buildings and surrounding community have been preserved as a historical site and museum, providing a glimpse into Lebanon County's industrial past. The site is the only intact charcoal-burning iron blast furnace in its original plantation in the western hemisphere. Established by Peter Grubb in 1742, Cornwall Furnace was operated during the Revolution by his sons Curtis and Peter Jr. who were major arms providers to George Washington. Robert Coleman acquired Cornwall Furnace after the Revolution and became Pennsylvania's first millionaire. Ownership of the furnace and its surroundings was transferred to the Commonwealth of Pennsylvania in 1932.
Cornwall Iron Furnace was one of many ironworks that were built in Pennsylvania over a sixty-year period, from 1716 to 1776. There were at least 21 blast furnaces, 45 forges, four bloomeries, six steel furnaces, three slitting mills, two plate mills, and one wire mill in operation in Colonial Pennsylvania.
The furnaces at Cornwall Furnace went through two stages of technology. Peter Grubb was born in Delaware about 1702 and settled in what is now Lebanon County in 1734. He bought about 300 acres (1.2 km2) of magnetite rich land. Grubb also noticed that his land had the other natural resources needed to produce iron. Namely, vast stands of timber for the production of charcoal, running water to operate the bellows, and an ample supply of limestone needed to add flux to the smelting furnaces. Grubb's plans were further helped by the fact that the magnetite at Cornwall was either very close to or on the surface of his land. He was ready to venture into the iron business and set about the task of building an iron "plantation". These centers of iron production were usually located well away from the heavily cleared farmlands and were nestled in the Ridge and Valley section of Pennsylvania. Grubb constructed his furnaces, first a bloomery and later the more modern charcoal-fired blast furnace and the support buildings and mill village that was needed to house his workers. He named his operation Cornwall because his father, John Grubb had come from Cornwall, UK in 1677. Cornwall Iron Furnace was an excellent fit for the agricultural based economy of the Thirteen Colonies. Iron was needed to make into tools, nails and weapons. The official policy of Great Britain frowned on manufacturing in the colonies, but England was no longer able to produce the needed iron for its needs let alone the needs of the colonists. In fact England had become dependent on importing iron from Sweden.
Peter Grubb was not really an ironmaster, but a builder. In 1745 he leased the ironworks to a consortium, Cury and Company, for 25 years and returned to Wilmington. The consortium continued the operation, with ownership passing to Peter's sons, Curtis and Peter Jr., after his death in 1754. The brothers took over the operation in 1765 and ran it quite successfully until the late 1780s. Curtis operated the Cornwall Furnace and lived on site; c1773 he built the original 19 rooms of the mansion that still stands prominently next to the property. Peter Jr. ran a forge at Hopewell, refining the pig iron produced by the furnace into more valuable bar iron. The ironworks were major suppliers to the Revolutionary War effort, and George Washington once visited to inspect the operation. Unfortunately for the Grubb family, as described in Curtis Grubb's biography, they were unable to retain control of the operation after Curtis' marriage in 1783. Most of the Grubb's holdings gradually fell into the hands of Robert Coleman, culminating in 1798. Coleman's son, William, was named manager of Cornwall Furnace and lived in the mansion; in 1865 the Colemans remodeled it into the 29 room structure known today as Buckingham Mansion.
In American Colonial history, the Iron Act, passed in 1750, was part of the British legislation designed to encourage the production of raw materials (including pig iron) in colonial America, but to restrict their manufacture there into finished iron goods. Existing manufacturing works could continue, but new ones for certain processes were prohibited.
The first furnace built by Peter Grubb at Cornwall Iron Furnace was a bloomery. Grubb built this in 1737 to test the market value of his ore. It was an economical way to test the market without having to invest in building the much more efficient and profitable blast furnace.
A bloomery is basically an enlarged blacksmith's hearth. It consists of a pit or chimney with heat-resistant walls made of earth, clay, or stone. (Sandstone was used at Cornwall.) Near the bottom, one or more clay pipes enter through the side walls. These pipes, called tuyeres, allow air to enter the furnace, either by natural draft or by forced with a bellows. An opening at the bottom of the bloomery may be used to remove the bloom, or the bloomery can be tipped over and the bloom removed from the bottom.
The first step taken before the bloomery can be used is the preparation of the charcoal and the iron ore. The charcoal is produced by heating wood to produce the nearly pure carbon fuel needed for the refining process. The ore is broken into small pieces and roasted in a fire to remove any moisture in the ore. Any large impurities in the ore can be crushed and removed. Since slag from previous blooms may have a high iron content, slag from previous blooms can be broken up and recycled into the bloomery with the new ore.
In operation, the bloomery is preheated by burning charcoal, and once hot, iron ore and additional charcoal are introduced through the top, in a roughly one-to-one ratio. Inside the furnace, carbon monoxide from the incomplete combustion of the charcoal reduces the iron oxides in the ore to metallic iron, without melting the ore; this allows the bloomery to operate at lower temperatures than the melting temperature of the ore. Since the desired product of a bloomery is easily forgeable, nearly pure iron, with a low carbon content, the temperature and ratio of charcoal to iron ore must be carefully controlled to keep the iron from absorbing the carbon and becoming unforgeable. Limestone could also be added to the bloomery, about 10% of the ore weight, which would act as flux and help carry away impurities.
The small particles of iron produced in this way fall to the bottom of the furnace and become welded together to form a spongy mass of the bloom. The bottom of the furnace also fills with molten slag, often consisting of fayalite, a compound of silicon, oxygen and iron mixed with other impurities from the ore. Because the bloom is highly porous, and its open spaces are full of slag, the bloom must later be reheated and beaten with a hammer to drive the molten slag out of it. Iron treated this way is said to be wrought, and the resulting nearly pure iron wrought iron .
In 1742, Grubb replaced his bloomery with a 30-foot (9.1 m) high charcoal-fired cold blast furnace. The blast furnace burned hotter than the bloomery and was able to render molten pig iron ("charcoal iron") from the ore.
A blast furnace relies on the fact that the unwanted silicon and other impurities are lighter than the molten iron that is the main product. Grubb's furnace was built in the form of a tall chimney-like structure lined with refractory brick. Charcoal, limestone and iron ore (iron oxide) were poured in at the top, and air was blown in through tuyeres near the base. The resulting "blast" promotes combustion of the charcoal (more modern furnaces use coke or even anthracite), creating a chemical reaction that reduces the iron oxide to the base metal which sinks to the bottom of the furnace. The exact nature of the reaction is:
More precisely, the compressed air blown into the furnace reacts with the carbon in the fuel to produce carbon monoxide, which then mixes with the iron oxide, reacting chemically to produce iron and carbon dioxide, which leaks out of the furnace at the top. In the beginning of the reaction cycle, the hot blast, also called "wind", containing pre-heated gas from Cowper stoves and air, is blasted into the furnace through tuyeres. The wind will ignite the coke and the Boudouard reaction will take place:
C + O2 → CO2
CO2 + C → 2 CO
The temperature in the furnace typically runs at about 1500 °C, which is enough to also decompose limestone (calcium carbonate) into calcium oxide and additional carbon dioxide:
CaCO3 → CaO + CO2
The calcium oxide reacts with various acidic impurities in the iron (notably silica), forming a slag containing calcium silicate, Ca Si O 3 which floats on the iron.
The pig iron produced by the blast furnace is not useful for most purposes due to its high carbon content, around 4-5%, making it very brittle. Some pig iron is used to make cast iron goods, often being remelted in a foundry cupola.
For other purposes further processing is needed to reduce the carbon content to enable iron to be used for tools or as a construction material. There have been various processes for this. The earliest process was conducted in the finery forge. In the late 18th century, this began to be displaced by 'potting and stamping', but the most successful new process of the Industrial Revolution period was puddling.
This is now done by forcing a jet of high-pressure oxygen into a special rotating container containing the pig iron. Some of the carbon is oxidised into carbon monoxide, CO, and carbon dioxide, CO2. This also oxidizes impurities in the pig iron. The container is rotated and the processed pig iron can be separated from the oxidised impurities. Before the mid 19th century, pig iron from the blast furnace was made into wrought iron, which is commercially pure iron. At that period, if steel was needed, particularly pure varieties of iron were heated with charcoal in a cementation furnace to produce blister steel (with about 1-2% carbon). This might be further purified using the crucible technique, but steel was too expensive to use on a large scale. However, with the introduction of the Bessemer process in the late 1850s and then other processes, the production of steel was dramatically increased. By the late 19th century most iron was being converted to steel before use.
The blast furnaces at Cornwall Furnace needed a tremendous amount of charcoal in order to keep them fired and thereby create a steady production of iron. The making of the charcoal became an industry in itself. Hardwood trees were chopped down, dried, stacked and fired in 30-to-40-foot-diameter (9.1 to 12.2 m) pits. A collier carefully stacked the wood around a chimney. The stack of wood was covered with leaves and dirt and was set on fire in the center. The fires were allowed to smolder for ten to fourteen days, under the careful, round the clock, supervision of the collier. The colliers were careful to make sure that enough heat was produced to expel moisture, tar and other substances from the wood without burning the wood up entirely. Wood was not charred until just before it was needed to keep it from getting wet and becoming useless. The demand for charcoal was so tremendous that Cornwall Furnace used an entire acre of wood every day for making charcoal.
The furnace operated twenty four hours a day, seven days a week, except for when it was closed for repairs. Cornwall Iron Furnace was capable of producing 24 tons of iron a week. [ citation needed ] A large waterwheel powered the bellows. Carts loaded with charcoal passed to and fro between the coal barn and the furnace under a protective roof designed to keep the charcoal dry. Other wagons hauled the ore from the mine to the top of the furnace on the hillside. Workers then manually transported the charcoal and ore to the furnace. The guttermen worked at the base of the furnace. They raked the cooling sand and dug channels for the molten pig iron. Next, they stacked the bars of pig iron outside. The working conditions were very difficult. Temperatures inside the casting house reached as high as 160 °F (71 °C).
Such a massive and difficult iron and charcoal making operation need a massive and hardened workforce. The furnace alone needed as many as sixty people working around the clock in twelve-hour shifts. The iron works support staff included a company clerk, a host of teamsters, woodcutters, the colliers, farmers and household servants. There was a wide gap between the classes. Workers were housed in small homes and worked very hard for low wages. The owners and supervisors of the furnace lived in mansions with sizable servant staffs. Historians have likened life at the furnace to life in a feudal barony.
There were three groups of workers at Cornwall Iron Furnace: Free labor, indentured servants and slaves. Slavery was legal in Pennsylvania until it was gradually abolished beginning in 1780 when the importation of slaves was prohibited. The management of the furnace had quite a bit of trouble with the staff of indentured servants. These unskilled workers were imported from Germany, England and Ireland. Many of them worked at Cornwall for a short time before eventually running away.
Robert Coleman rose from a holding clerkship at a prothonotary's office in Philadelphia to bookkeeper at Cornwall Iron Furnace to becoming Pennsylvania's first millionaire.
Coleman arrived in Philadelphia from Ireland in 1764. After serving as a clerk and bookkeeper he went on to acquire a lease on Salford Forge near Norristown in 1773 and immediately made a sizeable profit by manufacturing cannonballs and shot at Salford and Elizabeth Furnaces. He then used his profits to purchase a two thirds share of Elizabeth Furnace, shares of Cornwall and the Upper and Lower Hopewell Furnaces, (not the similarly named Hopewell Furnace), and ownership of Speedwell Forge. Soon Coleman was able to construct Colebrook Furnace, purchase the rest of Elizabeth Furnace and acquired 80% ownership of Cornwall Furnace and the ore mines nearby. His business acquisitions and the profits turned from them enabled him to become the first millionaire in the history of Pennsylvania.
George Dawson Coleman was the grandson of Robert Coleman and son of James Coleman. George Dawson Coleman married Deborah Brown of Philadelphia and had several children including Ann Coleman who moved to France and revitalized Château de Villandry (alongside her husband Joachim Carvallo).
George Dawson Coleman controlled much of the Coleman iron fortune with his brother, Robert. George acquired greater control of the ore mines at Cornwall and was able to experiment with iron furnaces that were fueled by anthracite coal instead of coke. He also invested in the expanding railroad, and built houses, a school and church for his employees. He was much loved by his community and went on to serve several times in the Pennsylvania State Legislature. (Several churches built by the Coleman family are still in existence in the area, and they are known as Coleman Chapels.)
George oversaw many improvements in production at Cornwall Iron Furnace. The bellows were replaced with "blowing tubs." The blowing tubs were piston-powered air pumps and containers that held compressed air and forced that air into the furnaces. The waterwheel was replaced by a steam engine in 1841. And the furnace stack was rebuilt in the 1850s.
The Colemans turned direct supervision of Cornwall Iron Furnace to John Reynolds in 1848, who acted as the guardian of the minor children of Thomas B. Coleman. He was the father of John F. Reynolds, a graduate of West Point. John Fulton Reynolds was commissioned a general and was the first Union General to fall at the Battle of Gettysburg. The elder Reynolds managed the furnace until his death in 1853.
Robert Habersham Coleman was the fourth and last generation scion of the Colemans. He shut the facility in 1883, opening new facilities for the company. In 1881, at the time he took over his family's business, Coleman was worth about seven million dollars. By 1889 he was estimated to be worth thirty million dollars. By 1893 the fortune had vanished. One of his homes, Cornwall Hall, was a "symbol of the rise, fame and decline of the "king" of Cornwall (Pennsylvania) during America's Gilded Age."
Cornwall Iron Furnace became obsolete by the 1880s. The Bessemer and open-hearth processes of creating steel, the replacement of charcoal with coke and anthracite coal, the discovery of iron deposits at the Iron Range in Minnesota near Lake Superior, and the building of modern factories in Pittsburgh, Steelton and Bethlehem brought about the end of iron production in Cornwall. Cornwall Furnace no longer earned a profit in its last ten years of operation and the last owner, Robert Habersham Coleman, had it shut down on February 11, 1883. In 1932, the furnace and ancillary buildings were deeded by Margaret Coleman Buckingham and have since been restored and open to the public.
Smelting is a process of applying heat and a chemical reducing agent to an ore to extract a desired base metal product. It is a form of extractive metallurgy that is used to obtain many metals such as iron, copper, silver, tin, lead and zinc. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or slag and leaving the metal behind. The reducing agent is commonly a fossil-fuel source of carbon, such as carbon monoxide from incomplete combustion of coke—or, in earlier times, of charcoal. The oxygen in the ore binds to carbon at high temperatures, as the chemical potential energy of the bonds in carbon dioxide is lower than that of the bonds in the ore.
The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is removal of impurities from the iron by oxidation with air being blown through the molten iron. The oxidation also raises the temperature of the iron mass and keeps it molten.
Pig iron, also known as crude iron, is an intermediate good used by the iron industry in the production of steel. It is developed by smelting iron ore in a blast furnace. Pig iron has a high carbon content, typically 3.8–4.7%, along with silica and other dross, which makes it brittle and not useful directly as a material except for limited applications.
Wrought iron is an iron alloy with a very low carbon content in contrast to that of cast iron. It is a semi-fused mass of iron with fibrous slag inclusions, which give it a wood-like "grain" that is visible when it is etched, rusted, or bent to failure. Wrought iron is tough, malleable, ductile, corrosion resistant, and easily forge welded, but is more difficult to weld electrically.
Steelmaking is the process of producing steel from iron ore and/or scrap. In steelmaking, impurities such as nitrogen, silicon, phosphorus, sulfur and excess carbon are removed from the sourced iron, and alloying elements such as manganese, nickel, chromium, carbon and vanadium are added to produce different grades of steel.
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. Blast refers to the combustion air being supplied above atmospheric pressure.
Basic oxygen steelmaking, also known as Linz-Donawitz steelmaking or the oxygen converter process, is a method of primary steelmaking in which carbon-rich molten pig iron is made into steel. Blowing oxygen through molten pig iron lowers the carbon content of the alloy and changes it into low-carbon steel. The process is known as basic because fluxes of calcium oxide or dolomite, which are chemical bases, are added to promote the removal of impurities and protect the lining of the converter.
The Wealden iron industry was located in the Weald of south-eastern England. It was formerly an important industry, producing a large proportion of the bar iron made in England in the 16th century and most British cannon until about 1770. Ironmaking in the Weald used ironstone from various clay beds, and was fuelled by charcoal made from trees in the heavily wooded landscape. The industry in the Weald declined when ironmaking began to be fuelled by coke made from coal, which does not occur accessibly in the area.
An open-hearth furnace or open hearth furnace is any of several kinds of industrial furnace in which excess carbon and other impurities are burnt out of pig iron to produce steel. Because steel is difficult to manufacture owing to its high melting point, normal fuels and furnaces were insufficient for mass production of steel, and the open-hearth type of furnace was one of several technologies developed in the nineteenth century to overcome this difficulty. Compared with the Bessemer process, which it displaced, its main advantages were that it did not expose the steel to excessive nitrogen, was easier to control, and permitted the melting and refining of large amounts of scrap iron and steel.
A bloomery is a type of metallurgical furnace once used widely for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. Bloomeries produce a porous mass of iron and slag called a bloom. The mix of slag and iron in the bloom, termed sponge iron, is usually consolidated and further forged into wrought iron. Blast furnaces, which produce pig iron, have largely superseded bloomeries.
Puddling is the process of converting pig iron to bar (wrought) iron in a coal fired reverberatory furnace. It was developed in England during the 1780s. The molten pig iron was stirred in a reverberatory furnace, in an oxidizing environment to burn the carbon, resulting in wrought iron. It was one of the most important processes for making the first appreciable volumes of valuable and useful bar iron without the use of charcoal. Eventually, the furnace would be used to make small quantities of specialty steels.
Direct reduced iron (DRI), also called sponge iron, is produced from the direct reduction of iron ore into iron by a reducing gas which contains elemental carbon and/or hydrogen. When hydrogen is used as the reducing gas there are no greenhouse gases produced. Many ores are suitable for direct reduction.
A finery forge is a forge used to produce wrought iron from pig iron by decarburization in a process called "fining" which involved liquifying cast iron in a fining hearth and removing carbon from the molten cast iron through oxidation. Finery forges were used as early as the 3rd century BC in China. The finery forge process was replaced by the puddling process and the roller mill, both developed by Henry Cort in 1783–4, but not becoming widespread until after 1800.
A Walloon forge is a type of finery forge that decarbonizes pig iron into wrought iron.
Ferrous metallurgy is the metallurgy of iron and its alloys. The earliest surviving prehistoric iron artifacts, from the 4th millennium BC in Egypt, were made from meteoritic iron-nickel. It is not known when or where the smelting of iron from ores began, but by the end of the 2nd millennium BC iron was being produced from iron ores in the region from Greece to India, The use of wrought iron was known by the 1st millennium BC, and its spread defined the Iron Age. During the medieval period, smiths in Europe found a way of producing wrought iron from cast iron, in this context known as pig iron, using finery forges. All these processes required charcoal as fuel.
In metallurgy, refining consists of purifying an impure metal. It is to be distinguished from other processes such as smelting and calcining in that those two involve a chemical change to the raw material, whereas in refining the final material is chemically identical to the raw material. Refining thus increases the purity of the raw material via processing. There are many processes including pyrometallurgical and hydrometallurgical techniques.
A cupola or cupola furnace is a melting device used in foundries that can be used to melt cast iron, Ni-resist iron and some bronzes. The cupola can be made almost any practical size. The size of a cupola is expressed in diameters and can range from 1.5 to 13 feet. The overall shape is cylindrical and the equipment is arranged vertically, usually supported by four legs. The overall look is similar to a large smokestack.
The Grubb Family Iron Dynasty was a succession of iron manufacturing enterprises owned and operated by Grubb family members for more than 165 years. Collectively, they were Pennsylvania's leading iron manufacturer between 1840 and 1870.
Archaeometallurgical slag is slag discovered and studied in the context of archaeology. Slag, the byproduct of iron-working processes such as smelting or smithing, is left at the iron-working site rather than being moved away with the product. As it weathers well, it is readily available for study. The size, shape, chemical composition and microstructure of slag are determined by features of the iron-working processes used at the time of its formation.
In 2022, the United States was the world’s third-largest producer of raw steel, and the sixth-largest producer of pig iron. The industry produced 29 million metric tons of pig iron and 88 million tons of steel. Most iron and steel in the United States is now made from iron and steel scrap, rather than iron ore. The United States is also a major importer of iron and steel, as well as iron and steel products.