Since the creation of fire, man has shaped metal into tools and other things. Iron was one of the first metals that man shaped. In the early nineteenth-century the Shenandoah Valley made iron one of its prime sources of income. The blast furnace was one essential aspect that led to the success of the manufacturing of iron in the Valley.

The location of a blast furnace was key to its operation. Furnaces were located near a source of ore. This was very important, because you did not want to waste resources such as labor to haul the ore to the furnace. It was also beneficial for its location to be near a source of flux, which was used to remove the impurities from the ore in the form of slag. Limestone was used as flux in the Valley. Fuel for the furnace also had to be present. Charcoal was used to fuel the furnace, so wood or forest areas were important. Hauling lightweight charcoal was not a problem, so its source could be farther away than the source of heavier ore or flux. Furnaces were also dug into or near banks. Banks served as ramps, so that ore and other material could be easily dumped into the furnace through the charging hole, which was at the top of the furnace. The bank also served in protecting the fire in the furnace from being disturbed, because the maintenance of a constant temperature was very important to the production of the iron. Another essential aspect of the location of the furnace was a water source. The furnace used the water as its power and as a source of transportation. Sometimes the readiness of a water source proved to be a problem due to Virginia’s occasional droughts (Brady, 2-3). The map (see figure 1) in Bond of Iron reveals that almost all forges are located near large secure bodies of water, like the North River (Maury River).

 
 

Figure 1 (picture from Dew, Charles in Bond of Iron)

 The design of the furnace was also important to its efficiency. A spot with good drainage is needed for a firm bed. The interior of the furnace must be able to withstand high temperatures, so firebrick is used for the interior. The hearth of the furnace was made of sandstone. For the exterior of the furnace, durable stone was used to absorb some of the pressure as well as to support the interior of the furnace (Clinton, 1-2). Throughout the Valley, blast furnaces can be seen to be pyramidal in shape. They are usually thirty to forty-feet tall. There was an opening at the top and usually three at the base of the furnace. The opening at the top was called the charging hole, which was used to add limestone, ore, and charcoal (see figure 2 for design). The central cavity of the furnace was called the bosh, and had a diameter starting at three feet and ending at about ten feet. The bosh then narrowed into the crucible, about two feet in diameter. One opening at the base was for the tuyere, the conduit that applies the blast. Another opening was the taphole, where molten iron would run onto the casting floor for molding, and the last opening, which was blocked by stone, was for the occasional cleaning of the crucible (Salmon, 23). Furnaces in the Valley used either waterpower or wind power for their bellows, which supplied air to the tuyere.

Before the furnace could be used, it had to be broken in. A new furnace had its lining washed with a composition of lime, clay, and salt in order to glaze the interior. This formed a protective layer, like when waxing a floor. A small fire was left in the furnace for about ten days with the top covered to allow it to dry out. After that the furnace was filled with coal in order to keep a fire burning for four days to heat and dry the furnace thoroughly. The furnace was then filled with alternating layers of ore and coal (or charcoal). The burning of the furnace was then monitored for a few days. The pressure of the furnace was increased gradually so the furnace can adjust properly. Clinton says that it should be kept at half pressure for the first few days and after the first week it should be increased gradually. The furnace should be running at full capacity in about four weeks (Clinton, 3). The breaking in of a new furnace was very important. If the furnace was not broken in, it could crack due to the rapid change in temperature.

The process involved in producing pig iron is very complex. The furnace is first filled with ore, flux, and charcoal. These are dumped into the bosh, from the opening at the top of the furnace, the charging hole. They are ignited and the air is supplied by the tuyere. Air came to the tuyere from large bellows, which were powered by a waterwheel or windmill. The furnace was then tapped off, and molten metal run off into molds of cast iron called sows and pigs. The molds are named sows and pigs, because it looks like little pigs feeding from their mother. The impurities, slag, were run off into a pit, where the slag cooled and hardened (Brady, 2). Not all ore was the same, so certain things were added into the mix to produce quality iron. If your ore contained too many sulfurs, large amounts of limestone could be added to carry off the sulfur, or slag. Too much, however, could also be a problem, because it could produce a brittle iron (Brady, 7). This is why the additives into the mix could vary day-to-day depending on the ore. The finished product was then taken to a forge to be refined.

The Shenandoah economy prospered due to the iron industry. The industry had its problems, though. Ore became scarce in the Valley. Forges would shut down, because ore deposits were low. This was a major problem at Bath Forge. Another problem came after the Civil War; when slavery was abolished the industry lost its labor force. Iron works were almost totally manned by slaves, because slave labor was skilled labor at a cheap price. After the Civil War forges all over the Valley shut down, because of limited ore deposits and slavery. Britain and the North were also a problem for the iron industry in the Valley. Britain flooded the market with good quality iron at lower prices. Britain had better technology that allowed them to produce iron cheaper than the forges in the Valley. Britain and the North were more industrialized in the industry.

Blast Furnace at William Weaver's Buffalo Forge in Rockbridge County (refer to figure 1)

 Blast Furnace designed under the General Education Program
 
 

1999 General Education Pilot Program Home