The Forge

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First published in the May 2025 Colerain Courier Newsletter

During some recent tours of Colerain Forges Mansion a few visitors asked me, “Where did the furnace sit?” The short answer to this question is that Colerain Forges did not have a furnace; it had forges. With this in mind, I thought I would take a few moments and write a few lines explaining what a forge is.

So, what is a forge?

The technical name would be a finery forge. What it did was refine pig iron from a blast furnace, which is high in carbon, into wrought iron. This would make it malleable for blacksmiths to work with. The type of refining mostly used in America would have been what was called the Walloon method. This method used two hearths in its process: the finery hearth and the chafery hearth. 

The process started with the pig iron being slid through the pig hole in the back of the finery forge into the finery hearth. Then, it was brought to melting temperatures by burning charcoal and air from the water wheel-operated bellows. As the bellows brought the metal to melting temperature, the air blast burned off the carbon in the pig iron. The melted metal trickled down to the bottom of the hearth, where the forgemen formed it into a ball and began to forge it under a large water-powered trip hammer, turning it into wrought iron by pounding out any impurities such as slag. The trip hammer would have been water wheel-operated and the head would have weighed around 500 lbs.

Once the ball of metal was formed into a more pure form of iron, it was called a bloom. Then, the bloom would be turned into a bar. At that point, the bar was called an anconie. The anconies would have been the shape of a dumbbell about 3 feet long, with one end slightly larger than the other. Upon formation, it was placed in a chafery hearth, heated to forging temperatures, and forged under the trip hammer into its final size. The size of the bar would be large, pure-wrought iron. The bars were shipped to a rolling and slitting mill to be worked down into more usable bars and plates.

Colerain Forges consisted of three forges: the upper and lower Sligo Forges and the Marshall Forge. The forges sat along the Spruce Creek, and this creek provided the power to operate their water wheels. Before the forges were consolidated into Colerain Forges, they purchased and processed pig iron into wrought iron from several blast furnaces in the local area. By the late 1820s, Colerain Forges were processing pig iron from Pennsylvania Furnace into blooms and shipping them to Sligo Iron Works in Pittsburgh.