In 1734, Peter Grubb acquired three hundred acres about five miles south of present-day Lebanon and found that its magnetite-rich iron ore was surrounded by the other elements needed for an iron plantation: flowing water to run bellows, timber for charcoal, and limestone to add flux to the iron smelting furnace. The magnetite ore not only was lower in oxide content that other ores, but at Cornwall it lay atop and only slightly below the earth's surface, another advantage for Grubb. America's early iron centers were usually located away from heavily cleared regions, and the need to house groups of workers created isolated plantation communities. Grubb began by building a bloomery, in 1737, to test the value of his ore. Bloomeries belonged to an older technology which blast furnaces were gradually replacing. Basically enlarged blacksmiths' hearths, the blooms-lumps of pasty iron-the bloomeries produced were an impure iron because the process only partially melted the iron ore. The blooms were than hammered to remove carbon, producing a wrought iron of inferior strength.

Replacing this with the superior technology of a thirty-foot high blast furnace in 1742, Peter Grubb turned out a highly carbonized but brittle iron. It was about this time he named the operation Cornwall for the county in England from which his family had emigrated.

Producing greater heat than any bloomery could, the furnace rendered molten iron from the ore. Impurities, including "sinter" (or cinders), silicates, and phosphorous were separated as slag and discarded, and a highly carbonized iron was drained into shaped areas of two types to cool and harden. Long depressions in sand produced irregular bars, called "pigs" because their formations resembled piglets nursing from a mother sow. If not made into pig iron, the molten iron was drained into forms for rigid objects such as cooking devices, stoves, and eventually cannon barrels. This was cast iron. Both cast iron and pig iron had high carbon content, but the pig iron was taken to iron forging facilities where heating and pounding turned it into quality wrought iron.

The blast which gave the technology its name was air forced in under pressure from leather bellows driven by a water wheel turned by the Furnace Creek. An arched recess in the side of the furnace contained the blast pipe, called the tuyere, which conducted the forced air into the furnace's fire. The blasts produced spurts of intense heat necessary to melt the ore. Temperatures rose to levels between 2650 and 3000 degrees Fahrenheit. In the crucible, or hearth at the bottom of the furnace, iron oxide in the ore was reduced as oxygen combined with the ascending carbon monoxide gas from the burning charcoal, generating, as end products, iron and carbon dioxide.

The furnace, built of native sandstone, stood on the side of a hill whose inclined path made it easy to raise charcoal, iron ore, and limestone flux the thirty feet to the top of the stack. A find grade of sandstone lined the stack, and clay or mortar filled the space between it and the outer stone.

Downward from the square opening at the top, the stack widened until it reached its center, the "bosh," which was nine feet wide. Below that, the furnace tapered inward to four feet at the hearth or crucible. This shape maximized the concentration of heat and the lower inward sloped walls were necessary to support part of the working mixture. Without this slope, the mix would have been so concentrated that the blast could not have passed through the mixture. Adjacent to the hearth was the casting house or shed in which both the cast objects and the iron bars were made.

Control was exercised by the founder, stationed at the top of the stack, called the tunnelhead. He determined the proportion of charcoal, ore, and limestone flux that made up the batch to be dropped in. These inserted materials were called the charge. He made his mix by deciding how many filled baskets of each of the three components to include, rather than precisely measuring or weighting the items. The heat was a variable of the quantity of charcoal in the charge. If the founder perceived that the furnace flames were dark, the furnace was not hot enough; if bright and smoky, there might be excess limestone or not enough ore.

The making of mass quantities of charcoal to fire the furnace was an industry in itself. Split wood-preferable hickory, chestnut, black oak, or white oak-was hauled to dry, level sits sheltered from the wind, free from stones but not loamy or sandy. The wood was made into charcoal by slowly roasting it in thirty-to forty-foot diameter hearths or "pits" under carefully controlled conditions. The collier stacked cordwood around a central chimney. This mound was then covered with leaves and dirt and set on fire at the center. Each pit took twenty-five to fifty cords. A collier carefully tended the smoldering wood around the clock for ten to fourteen days until it was completely charred. Enough heat had to be produced to expel tar, moisture, and other substances from the wood without consuming the wood itself. The collier located soft spots by jumping of the mound, then dug them out and refilled them. To avoid the possibility of the charcoal getting wet and becoming unusable, wood was usually cut and stored in the winter, and not charred until just before it was needed.