Iron production

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Iron production converts iron ore into pig iron through a process known as smelting. Early on in the history of iron production in the United States, most furnaces used charcoal as fuel; so charcoal production and iron production were often closely linked. In fact Charcoal was the only fuel for iron production until the 1830s when the industry began a slow transition toward the use coal as fuel[1]. Ironworks were some of the first and most enduring examples of industry in the United States. Remnants of ironworks can still be found, especially in rural parts of the country[2].


In the eighteenth and nineteenth centuries, small-scale metalworking operations produced everyday objects, such as kitchenware, toys, building materials, and tools[3]. During wartime, cannons and other military weaponry were cast at furnaces[4]. Iron plantations were typically in rural communities and often included forges, housing for workers, woodlands for charcoal production, and a sawmill[5]. Bloomeries were early centers of limited iron production. In a bloomery, the iron oxides in ore were reduced to metal and were then separated from the gangue in the ore. The fire created liquid slag and burning charcoal produced carbon dioxide, which reduced the oxide to metallic iron[6]. Blast furnaces were also used for larger-scale iron production. These furnaces could be twenty to thirty feet in height and had hollow centers into which were placed ore, fuel, and flux[7]. Bellows were powered by a water wheel, and melted iron and liquid slag accumulated in the bottom of the furnace[8]. By the nineteenth century, blast furnaces were the most commonly used type of furnace[9].

Late in the nineteenth century, the Lehigh Valley was second only to Pittsburgh, PA in the yearly value of iron products in the iron districts of the entire country and was ranked first in pig iron districts[10]. The Lehigh Valley had fifty anthracite coal furnaces, of which the Bethlehem Iron Company owned six[11].

In 1850 all of the ironworks in Eastern Pennsylvania were accounted for. In Lehigh County, there were six anthracite blast furnaces that were in blast and one that was out of blast. There was one hot blast charcoal furnace that was out of blast and one cold blast charcoal furnace that was out of blast. There were no forges and no rolling mills. In Carbon County there was one anthracite blast furnace in blast and one not in blast. There was one hot blast charcoal furnace in blast and one out of blast. There were no cold blast charcoal furnaces. There were four bloomeries, two forges, and no rolling mills[12].

Iron has been used for thousands of years since it was understood that iron ore could be heated to make it into a malleable material[13]. While a charcoal kiln site can be identified by brick or stone artifacts, it is harder to identify a charcoal mounds because it was made of wood and dirt[14].

Iron Communities

Self-sufficient communities, known as iron plantations, were built around these furnaces. A large amount of workers, both in terms of profession and number of employees, were needed to run an iron plantation. These jobs including colliers, miners, woodcutters, molders, founders, patternmakers, and their helpers. In Pennsylvania, Hopewell Furnace employed roughly two hundred to two hundred fifty people during the nineteenth century. Workers at iron plantations would often bring their families along with them. Considering this, the community at Hopewell Furnace would have consisted of about six hundred people[15]. The lands of iron plantations included housing, gristmill, and sawmills, farming land, and vast amounts of woodland, as well as barns, company stores, spring-houses, blacksmiths, schools, churches, carpenter's shops, forges, casting houses, charcoal storage, and many other buildings[16]. Iron production required over a hundred acres of woodlands per year[17].

In the 18th and 19th centuries, there would have been hundreds of iron furnaces, and each town most likely had a blacksmith and forge[18]. Charcoal mounds and kilns were located as close to the wood source as possible, since wood was heavier to move than the charcoal so they were not usually near roads, but were on the sides of hills[19]. Ironmakers hammer or roll the wrought iron to fit the buyer's preference, which might include bars, rods, or sheets[20].


Prior to the 1830s, every furnace in the US burned charcoal as fuel. Charcoal was used because it could be produced in large quantities, it burns hotter than wood, and it is almost pure carbon, so it reduces impurities in iron produced[21]. To make charcoal, a variety of methods were used including hearths and kilns. Hearths were generally used in the pre-Civil War period and involved burning wood in earth-covered mounds. These hearths produced weak charcoal that would crumble easily[22]. Charcoal kilns were made of brick and were more efficient. They also created more durable charcoal than hearths, which yielded charcoal that was more brittle[23]. Kiln remains vary greatly. Smaller remains are usually those of farm kilns, which can be found at the base of hills with roads nearby, while larger remains oriented with a square stone base and occasional steel shells surrounding the base are commercial kilns, and usually placed near railroads. Commercial kiln locations can be found on historical maps from the nineteenth and early twentieth century[24]. Early finers had to use about 2 to 3 pounds of charcoal in order to produce a pound of iron[25]. Around the 1860s, coal and coke began to replace charcoal in some areas[26]; but overall, iron production increased so much that the use of charcoal continued to rise until 1890. At this time charcoal began to decline in use and instead coke furnaces were taking the front stage. By the 1890s there were less than 100 charcoal furnaces in use[27]. Coke furnaces were larger and like their charcoal fueled relatives, would need to have air being blown into the furnace so that it is able to continuously operate for months on end. Around the same time, perpetual kilns were introduced. These kilns can be characterized by three types of operation, mixed feed, separate-feed, and rotary kilns. Mix feed kilns were the most difficult to manage, the limestone and fuel had to be fed in alternative layers. When running favorable these kilns were the most economically favorable. The next type of kiln is the separate feed kiln. These became the first modern lime kiln which uses limestone and fuel not in direct contact. The last type is the rotary kiln. These kilns are horizontal and resemble long pipes that rotate on rollers[28]. They required that the limestone be crushed fairly small and even. One downside for rotary kilns is that they use a lot of fuel[29]. The last charcoal-powered furnace in the United States was in blast until 1945[30]. Charcoal pits produced weak charcoal that would easily crumble when it was put in the blast furnace, while charcoal kilns produced more durable charcoal (McVarish p. 262)

Prior to the advent of puddling furnaces coal was never a viable option for iron production because it would contaminate the metal with sulfur [31].


Furnace efficiency varied within the industry; the type of ore, equipment used, region, charcoal quality, and furnace type contributed to this[32]. Ironworks had to be near water and sources of raw materials such as charcoal, limestone, and iron ore[33]. Colonial ironworks used a variety of techniques to produce iron.


A bloomery was a small operation that heated iron ore to refine and shape it, which produced wrought iron[34]. Bloomeries needed simple equipment like a hearth, bellows, and tools for manipulating the iron[35]. After heating, iron ore became wrought iron, and these slabs of wrought iron were called blooms[36]. They had to simultaneously accomplish two tasks: reducing the iron oxides in the ore to metal, and also to separate the metal from the gangue in the ore[37]. Bloomeries were common in colonial America, specifically in Massachusetts, New Jersey, and Pennsylvania. They operated between the seventeenth and twentieth centuries. Some disadvantages of bloomeries included limited production, wasted heat, and an inability to completely separate the iron from slag[38]. Because bloomeries were a small operation, they created limited production. A bloomery could be able to supply a small blacksmith with what they need to satisfy local customers but never enough to satisfy a market.[39] A bloomery cannot run continuously like blast furnace and because when the bloomer had to remove the loup from the hearth, thermal energy was wasted.[40].

Blast Furnace

The introduction of the blast furnaces addressed many of the disadvantages of bloomeries. Blast furnaces had the ability to run continuously for months at a time, conserve heat, and produce a much greater output. A blast furnace would have been constructed in a dry location that was not prone to flooding[41]. After establishing a location that fit this criterion, the ground would be excavated to ensure that it could support the weight of the stack[42]. The foundation for the furnace would be constructed so that an additional foot of foundation would extend past the base of the furnace in all directions[43]. Blast furnaces were vertical, hollow structures, the top of which would be loaded with ore, fuel, and flux. The bottom had air vents and a hole for the molten iron to run out. Blast furnaces tended to be constructed twenty-five to thirty feet high when they first came into use, and eventually grew to be thirty-two to forty feet high during the nineteenth century with a conical shape on top[44].

The blast furnaces had very thick stone walls with fire-resistant interior lining. A layer between the lining and outer stones — usually made of clay or smaller stones — provided better insulation and allowed the inner walls to expand slightly when heated[45]. The outer wall was generally constructed of any stone, often granite, grauwach (a dark coarsegrained sedimentary stone), or slate[46]. The inner walls of the furnace were essential to build adequately as it had to stand up to high heat over long periods of time. The hearths in the blast furnaces were typically constructed from sandstone[47]. Bellows, which pumped air into the furnace to feed the flames, were often powered by waterwheels, equal to about twenty horsepower. By adjusting ventilation, the temperature inside blast furnaces could be controlled to a degree. Blast furnaces were loaded from the top and therefore were often located along hillsides. When the molten iron was ready to be collected or tapped, a smaller hole at the top was opened to allow the liquid slag, which sat on top of the iron because it was lighter, to be drawn away. After the slag was collected, the main plug was pulled, and the molten iron ran into sand molds. The iron produced in blast furnaces is called pig iron because the final product resembles piglets suckling on their mother. After the iron ran into the molds and was cooled, the "pigs" were broken off the "sows." These smaller pieces were more valuable than the metal in the runners which would need to be remelted[48]. In Pennsylvania, furnaces made roughly ten to twenty-five tons of pig iron or castings per week, with the latter amount rarely being attained[49]. By the nineteenth century, the reduction of iron took place almost exclusively in blast furnaces. A blast furnace was filled with three materials, iron ore, charcoal and limestone. Iron ore could be found in bogs and deposits near the ground[50]. By the early 20th century, iron furnaces started using coke and coal instead of charcoal[51]. Charcoal and early coke furnaces were similar in construction, the only differences were that coke furnaces generally were larger and required a higher pressure blast[52].

The Fining Process

The Fining Process was brought to the United States in the seventeenth-century. Finer workers would melt pig iron and allow the carbon to oxidize. The iron gathered into a mass called a loup and was then hammered until the slag was removed[53]. These early iron masters had to use charcoal as their main source of fuel as no effective way to use coal as fuel had been developed yet[54]. For each pound of iron produced a finer had to burn about 2 to 3 pounds of charcoal for fuel[55].

Walloon Process

The Walloon Process was the original fining technique. The Walloon Process involved pushing a pig of iron into a hearth full of charcoal at a downward angle to melt it, working it into a loup, and hammering it to expel slag. The melted metal was then collected from the bottom of the hearth and brought it into the air blast[56]. This air blast came about through the tuyere, a nozzle usually constructed of iron[57]. From here the finer kept the metal in the air blast until they were convinced that all the silicon and carbon had already oxidized [58]. It was after the oxidation that the metal was worked into a loup and then hammered to remove the slag[59]. Occasionally the loup was reheated during the hammering process[60]. The Walloon Process required a lot of air to heat the flames and the quality of wrought iron produced was heavily dependent on the skill of the workers making it[61].

Lancashire (Charcoal Hearth) Process

The Lancashire Process, which was developed in Sweden, involved moving the pig iron through the hottest part of a flame to burn off impurities and allowing the melted iron to accumulate at the bottom. Workers would then lift the iron, cut into it, and force slag in to oxidize what impurities remained. The iron was then broken up, remelted, and formed into a loup via hammering. The Lancashire Process reused heat from the flames to preheat air being pumped in by the bellows, making it more heat-efficient than the Walloon Process[62].

In the United States this process was referred to as the "Charcoal Hearth Process"[63]. The firing hearth stood at about 4 feet tall and was comprised of water-cooled cast-iron pipes[64]. This method of iron production made purer iron than that of the Walloon process as the iron from the Lancashire process contained less carbon and slag [65].


Puddling was a process to produce wrought on iron on a larger scale. This method was able to use mineral coals instead of charcoal. To prevent impurities from the coal from contaminating the iron, puddling placed the coal in an adjacent chamber to the iron, where most of the heat reached the iron by reflecting off the ceiling. This is where the name "puddling" comes from[66]. Puddlers could handle three times as much iron as a finer, up to six hundred pounds at a time. Workers would push any solidifying clumps of iron under the surface of the molten mix so they would not oxidize. After most of the impurities had oxidized, a worker would split the iron into three lumps, which would be pressed by a machine called a squeezer to remove the remaining liquid slag[67]. The bosh of the furnace was typically constructed from soapstone in Pennsylvania[68].


Forging produced wrought iron using blooms and rods by effectively hammering. Large hammers between fifty and four hundred pounds could be used; lighter hammers typically produced smaller things. Forging hammers were later automated by the waterwheel and steam power. If the motive power was water, a waterwheel was directly fastened to the shaft. If the motive power was steam, a flywheel was attached and the power conveyed by leather straps or belt[69]. With these processes, the automated hammer could strike up to two hundred and fifty times per minute with around 50 pounds of force[70].

A finer would burn about 2 to 3 pounds of charcoal for every pound of iron made[71]. Artisans found that iron and steel were easier to mold when hot. For more efficient use, English engineers created a looping mill to better mold the iron and steel[72].

The Furnace

The upper portion of the furnace was conical in shape. The walls had an inner and outer layer; the outer was usually made of granite or slate, while the inner was usually made of sandstone or firebrick because of these substances' durability to withstand high temperatures[73]. Between the two walls was an eight-inch space filled with stone chips or broken cinder-blocks. This space allowed the inner wall to expand and contract comfortably without bursting the outer wall. The area where workers would empty wheelbarrows full of iron ore was called the "trunnel head" or "throat." The opening above the hearth of the shaft below the trunnel head was called the bosh, which supported the furnace burden while funneling the molten slag[74]. The taper of the shaft, bosh, and crucible was entirely dependent on the type of ore smelted, charcoal quality, and what quality of iron was desired as the finished product. In the United States, a straight, uniform forty to fifty-foot stack was needed when hydrates and oxides of iron were smelted. Heat-exchanges, or hot blast stoves, were installed in the nineteenth century to increase efficiency. By the early twentieth century, the iron furnaces were forced to change due to the moving times. They grew to be about eighty feet tall; the shape and proportion of the hearth and bosh and the addition of a bellhopper to the trunnel head allowed for the use of new materials[75]. As coke-burning furnaces were built, the demand for charcoal declined. The transition to coke fuel caused some modifications to the furnace's structure[76]. Coke powered furnaces were typically taller and had higher blast pressure than their charcoal counterparts[77]. There were approximately 500 in the 1860s, but by 1900 there were less than 50[78]. Americans left the English practice by adopting gas fired furnaces soon as they started making crucible steel.[79]


There were several different positions that could be held within the iron works. The Lives of Workers varied as working at the furnace required people of numerous skill sets, resulting in different pay levels and hours worked[80]. The furnaces needed managers, clerks, molders, teamsters[81], blacksmiths[82], woodcutters[83], colliers involved in charcoal production, ironmasters[84], and fillers[85]. Furnaces also required founders, who supervised the actual operation of the foundry. Founders typically made their way up the ranks to founder by beginning as a laborer, becoming a helper, then a keeper (assistant to the founder), and finally a founder[86].


  1. Straka 2014, 104
  2. McVarish 2008, 259
  3. McVarish 2008, 259
  4. Swank 1884, 35
  5. McVarish 2008, 259
  6. McVarish 2008, 260
  7. McVarish 2008, 260
  8. McVarish 2008, 260
  9. McVarish 2008, 266
  10. Swank 1884, 34
  11. Swank 1884, 34
  12. Convention of Iron Masters 1850, 135
  13. McVarish 2008, 259
  14. McVarish 2008, 263
  15. McVarish 2008, 259
  16. McVarish 2008, 259
  17. Straka 2014, 105
  18. McVarish 2008 259
  19. McVarish 2008, 263
  20. McVarish 2008, 278
  21. McVarish 2008, 260
  22. McVarish 2008, 262
  23. McVarish 2008, 262
  24. McVarish 2008, 265
  25. McVarish 2008, 268
  26. McVarish 2008, 267
  27. McVarish 2008,263
  28. McVarish 2008, 264
  29. Straka 2014, 264
  30. Straka 2014, 104
  31. McVarish, 2008, 269
  32. Straka 2014, 105
  33. McVarish 2008, 259
  34. McVarish 2008, 259
  35. McVarish 2008, 260
  36. McVarish 2008, 259
  37. McVarish 2008, 260
  38. McVarish 2008, 260
  39. McVarish 2008, 260
  40. McVarish 2008, 260
  41. Overman 1854, 153
  42. Overman 1854, 153-154
  43. Overman 1854, 154
  44. McVarish 2008, 262
  45. McVarish 2008, 262
  46. McVarish 2008, 266
  47. Overman 1854, 183-184
  48. McVarish 2008, 265
  49. Swank 1884, 35
  50. McVarish 2008, 260
  51. McVarish 2008, 267
  52. McVarish 2008, 268
  53. McVarish 2008, 268
  54. McVarish 2008, 268
  55. McVarish 2008, 268
  56. McVarish, 2008, 268
  57. McVarish, 2008, 285
  58. McVarish, 2008, 268
  59. McVarish, 2008, 268
  60. McVarish, 2008, 268
  61. McVarish, 2008, 268
  62. McVarish 2008, 268-269
  63. McVarish, 2008, 268
  64. McVarish, 2008, 268
  65. McVarish, 2008, 268
  66. McVarish 2008, 269
  67. McVarish 2008, 270
  68. Overman 1854, 273
  69. McVarish 2008, 270
  70. McVarish 2008, 271
  71. McVarish 2008, 268
  72. McVarish 2008, 280
  73. McVarish 2008, 266
  74. McVarish 2008, 266
  75. McVarish 2008, 267
  76. McVarish 2008, 267
  77. McVarish 2008, 267
  78. McVarish 2008, 263
  79. McVarish 2008, 271
  80. Walker 1966, 229
  81. Walker 1966, 231
  82. Walker 1966, 237
  83. Walker 1966, 238
  84. Walker 1966, 248
  85. Walker 1966, 235
  86. Walker 1966, 232


  • McVarish, Douglas C. 2008. American Industrial Archaeology: A Field Guide. Walnut Creek, Calif.: Left Coast Press, Inc.
  • Straka, T. J. 2014. Historic Charcoal Production in the US and Forest Depletion: Development of Production Parameters. Advances in Historical Studies, 3, 104-114.
    • Walker, Joseph E. 1966. Hopewell Village; a Social and Economic History of an Iron-Making Community. Philadelphia: Univ. of Pennsylvania Press.