The furnace itself was built 25 to 30 feet high with a hearth or a crucible where the molten iron was collected, perhaps a foot or two deep and three or four feet wide. Just above the hearth the opening flared outward and was termed the "bosh." The bosh was about eight feet in diameter at its widest and narrowed as it converged toward the top.

The outside of the furnace was built of sandstone with a liner of firebrick. Furnaces were usually built with an incline just behind to ease charging and loading. The trestle leading to the charging point was usually built of heavy planks with a track on it. Men, often slaves, would roll wheelbarrows of raw materials over this trestle and dump them into the top of the furnace.

To produce one ton of iron, the furnace required an exact recipe of 200 bushels of charcoal, 2 tons of iron ore, and 500 pounds of limestone, all of which would be lit and joined inside the furnace. A waterwheel-powered bellows kept the fires hot. It took 4 to 6 hours to produce molten iron, with a layer of slag floating on top. The slag would be drained off through the "cinder hole," and then the molten iron would be drained through the "tap hole" below.

The slag would be added to the slag heap still visible in front of the furnace today, but the molten iron would be allowed to run down a narrow crevice in the sand into a corresponding and larger trench in the sand to cool into pig iron.

The daily product of the Newlee Iron Furnace was 3¼ tons, at a cost of $19.40 per ton in 1877 figures. The iron made at Cumberland Gap was shipped down Powell River to Chattanooga. This furnace was the only furnace in the Dyestone belt still using charcoal in 1877.