PA Technique of Colonial Iron Manufacture with Bio-Char
It was natural that men were attracted early to the manufacture of iron in Colonial America, for ore was plentiful. Acrelius, the Swedish pastor at Christina during the middle of the eighteenth century, wrote that there was more ore in Pennsylvania than the people could ever use. Iron deposits were found even among the loose stones on farm lands. The first ores used were those on the surface or just below; little technical knowledge and but a few simple tools were required to mine them. Trenches were dug, rarely more than 40 feet deep. When this depth was reached, new "mine holes" were started. Most of the Hopewell Furnace ores came from the Jones', St. Mary's, and Hopewell Mines, not far from the Village. Only a very few attempts were made at shaft mining before the Revolutionary War. Three or four good miners could generally supply all the ore needed for a single furnace.
Charcoal was the fuel used to smelt iron ore in America throughout the eighteenth century and the first three decades of the nineteenth. It made an ideal furnace fuel, being almost free of sulfur, and its ash, consisting largely of lime and alkalis, supplied part of the necessary flux. The charring was done in open piles, mostly during the winter months. Generally it was done in the woods adjacent to a furnace or forge, but sometimes within the limits of settled boroughs. The charcoal "pit," or "hearth," was simply a circular clearing, dry and level, about 30 to 50 feet in diameter. Workers, known as colliers, were required to "coal" the wood, which was cut into given lengths for this purpose by the woodchoppers and piled in the shape of a cone. As many as 10 or 12 colliers might be needed to keep a furnace going.
Making charcoal. This cross section of a pile of cordwood illustrates the manner of
stacking the wood reparatory to starting the "coaling" process.
The fire is started in the pocket made by the withdrawal of the center pole.
Frederick Overman, The Manufacture of Iron in All Its Branches,
When the piles were in process of charring, they had to be watched day and night. Thus the bleak and lonely colliers' huts were built in the silent forests, far from the plantation center where the other ironworkers lived. Hickory was the best wood for making charcoal, but black oak and chestnut, being more abundant, were generally used. The wood was not charred immediately after being cut, but only a short time before it was needed. Large as most of the strong-walled charcoal houses were, they could not hold enough fuel to feed the furnace for any great length of time, and to have left the charcoal outside would have made it unfit for use. An average furnace would consume perhaps 800 bushels of charcoal every 24 hours, and this required about 50 cords of wood of 20- to 25-year growth. Some furnaces consumed almost the yield of an acre of woodland each day. Perhaps the one disadvantage of charcoal as a fuel was its lightness, which made it easy to crush. This was the factor which limited the height of colonial furnaces to a maximum of about 35 feet.
Courtesy Chester County Historical Society.
