Today’s blast furnaces are distant cousins to the iron works of the early colonial era. One such operation – possibly the first successful iron works in the colonies – is the Tubal Works in Virginia. Started by Colonel Alexander Spotswood nearly 300 years ago, it later became known as Spotswood Furnace.
Spotswood was sent by Lord Orkney to be the Governor’s representative to the Virginia Colony in 1710. Having discovered iron ore and abundant natural resources, Spotswood appealed to Great Britain for the necessary funds to construct an iron enterprise. These funds were refused, so Spotswood built the Tubal iron blast furnace in 1714 with private funds. Slave labor was not prevalent at this time, and German indentured servants who knew the iron-making trade were brought in to a company town a few miles from the furnace. This town is still known as Germanna.
Prior to this time, “bloomeries” scattered throughout the colonies produced blooms, which were an impurity-filled spongy iron mass made from ore and charcoal. As mentioned in a previous NYK, it was illegal for the colonies to make value-added products. This is the likely reason funds were refused for the Tubal Furnace. Great Britain didn’t want the colonies to have the ability to create their own products because it would kill their revenue stream.
When you consider what it took to keep the Tubal blast furnace fed, it’s amazing that it was able to run continuously for five to nine months. Four times an hour, a charge of 30 bushels (600 pounds) of charcoal, 1,000 pounds of ore and 50 pounds of oyster shells were dumped into the furnace. The furnace was tapped from below, and molten iron flowed into sand molds (sows) and was further distributed into smaller bars called pigs (hence the name pig iron). Each pig was 48 x 6 x 3 inches and weighed 55-60 pounds. There were 34 pigs to the ton.
While blast-furnace operations are major undertakings today, it was quite a process in the early 18th century. Supplying the necessary charcoal – coke had not yet become commonplace – required seven cords of wood per ton of iron. The seven cords becomes 150-240 bushels of charcoal, and at a furnace like Tubal, 60,000-144,000 bushels would be needed annually. Doing the math, the annual charcoal usage for Tubal Furnace would consume 140 acres of timber.
The charcoal was only produced as needed because if it were exposed to the elements, it would spoil. Charcoal was produced on a large circular hearth 30-50 feet in diameter. A collier arranged a 30-cord stack of logs to minimize air spaces, lighted it from the top and then covered the pile with leaves and dirt. With constant attention, the pile never became inflamed and would become charcoal in 10-14 days. A single collier and two or three assistants usually monitored nine hearths, and they would supervise the daily transport of wagons that carried 100-300 bushels of charcoal the 2- to 5-mile distance to the furnace.
By 1732, the Spotswood iron empire – four blast furnaces and two forges – was one of the largest industrial operations on Earth. In fact, by 1750, most of the iron imported by England – 2,500 tons annually – was produced in Virginia. Having a facility such as Spotswood likely had a significant impact on our victory over Great Britain in our struggle for independence years later.
In 1820, a manufacturer’s census of the Antietam Iron Works indicated that 360,000 bushels of charcoal were needed annually for the blast furnace, forge and casting facility. That’s approximately 420 acres of trees each year. Fortunately, for the good of our forests, coke (made from coal) began to be used at Antietam in 1838. The availability of coal and easy access to transportation of raw materials and end product was key to the rise of Pittsburgh as the steelmaking capital of the U.S.
Now you know that the roots of today’s blast furnaces are found in the backcountry of colonial Virginia. IH