The Overly Iron Furnace Near Austin
We found proof that some Ohio fire pits, such as the Overly Furnace above, were iron furnaces. The best proof of this was gained from our 1992-93 excavation of a pit furnace in a cow pasture in southwestern Pickaway County, Ohio. The owners of this pasture land call it "Lynn Acres." Remains of this furnace were found mostly intact. We uncovered a deep bowl, its air duct and a work area in front of the air duct opening in the furnace wall. The Overly, Lynn Acres, and several other furnaces excavated in this area since 1949 used a 2,000 year old hearth matrix design to smelt iron. Proof that these Ohio furnaces are both prehistoric and pre-Columbian will be included in the author's book when it is published.
The Lynn excavation of 1992, below, shows these features: the smelting pit is at the top, showing the air duct which cuts across its bottom. The lower portion of this 1992 photo shows a shallow exposure of the work area. This work area was more fully excavated by the APGS in 1993.
The Lynn Acres Excavation
Artifacts recovered from the Lynn site, along with photos, were examined by Carroll Mobley, a professor of metallurgical engineering of The Ohio State University, Columbus, Ohio. The professor told us we had indeed found an iron furnace, based upon the evidence he was shown.
The Lynn Acres Furnace is an example of David Orr and I call the "Deer Creek" type, which we also classified as presumed historic. However, I was always a skeptic about this because of the economic considerations posed by the furnaces. These alone seem impossible to reconcile with the history of what became the Old Northwest Territory, which goes back to the early 1600s with the first French explorers. The evidence for the pre-Columbian origin of these furnaces will be fully developed in the author's book. Other furnaces of this type also exhibit the oval shape at the surface, and furnace sites are found with a very similar assortment of artifacts. These include slag, slag-glazed stones, baked clay, bog iron ore, charcoal, broken bricks, ashes, cinders, lime and iron artifacts. Where excavation has occurred, one or more furnace pits may be found.
The oval upper ring of the Lynn Furnace is approximately 9 by 8 feet in diameter and the bowl is 9 feet deep. The oval bowl descends to a linear bottom cut by an air duct. Evidence obtained from excavations indicates rounded stones were used at the bottom of the furnace bowl as a hearth to both support the fuel and ore, and furnish a blast of air.
The fact that such stones were part of a hearth matrix is easily inferred from adhesion marks, flow trails and frozen droplets of slag. The trails and droplets disclose the vertical orientation of a stone in such a hearth matrix. Also, many of these stones are coated with iron-slag and the color of the slag can indicate where a glazed stone was exposed to a reducing atmosphere (gray-green) or the oxygen-rich inflow of the air blast (orange).
The Lynn Acres excavation was the first and is so far the only scientific investigation of a natural draft pit iron furnace in America. Over 2,000 measurements of furnace features and artifact positions were taken in three dimensions, using measuring tapes and a plumb bob. An A-B baseline was surveyed and excavation levels established every 10 centimeters using a transit. Previous excavations of several of these furnaces by amateurs were not conducted using accepted archaeological methodology and only a few crude measurements were made.
No professional archaeologist has participated in an excavation of one of these furnaces, but we hope this can be arraigned in the future. Several good Deer Creek type sites exist which should contain intact or nearly intact furnaces here in Ohio, including one I discovered in Delaware County, Ohio in November, 1996, the Hoover Furnace. Diagnostic artifacts, such as stones glazed with iron slag, make finding such furnaces easy for experienced investigators of APGS once their occurrence is reported to us.
Bog iron ore, locally available in shallow deposits, was used in Ohio's natural draft pit iron furnaces burning charcoal fuel at around 2150 degrees Fahrenheit to produce wrought iron. The direct reduction process was employed to smelt wrought iron, the kind of iron blacksmiths used to make a wide range of useful tools and hardware items such as nails, rivets, and hinges.
Wrought iron can be hammered, bent and twisted into shapes desired by a blacksmith and one piece can easily be joined to another by welding. But true wrought iron is no longer made and has almost disappeared today, replaced by hollow or solid steel bars, which can be mass-produced.
True wrought iron can still be seen and appreciated in heavy old fencing surrounding some historic homes and buildings. Its production was a hot, labor-intensive task that required skilled ironworkers to produce relatively small batches of iron. The mass production of steel, beginning in the 1870s, led to the decline of wrought iron production and its eventual disappearance from the marketplace.
Even before the introduction of the mass production of steel, direct process iron furnaces were replaced by indirect process furnaces. The indirect process furnaces produced hot liquid iron which was poured into molds to form bars of cast iron. These bars were then processed further in other furnaces to produce wrought iron more efficiently and on a larger scale. Both direct and indirect process furnaces were used in America in the 18th and 19th centuries, but indirect process furnaces by far were more efficient and produced much larger quantities of iron.
The production of wrought iron in a direct reduction furnace requires both high temperatures and a chemical reaction.
Lynn Air Duct In Front of Furnace Bowl
The air inlet of the Lynn Acres furnace, above, was formed by walls of hand-made brick. The wall was at right angles to the brick-walled air duct, which runs under the furnace, extending back from the ruler. The duct averages about 15 inches high and wide; its dimensions varied slightly along its course. The stone slabs in front of the furnace were used to roof over the air duct.
Judging by evidence of iron slag on bricks found in the furnace, Orr and I believe a brick wall was used near grade level to retain the surface soil. These bricks are glazed only on one side, which must have been the side facing into the furnace. Hard-baked clay formed lower portions of the furnace bowl surface.
The extreme heat and possible repeated uses of the Lynn furnace is indicated by heavy glazing on many of the bricks we found. As is usual in metallurgical brickwork, clay was used as mortar for the bricks of the Lynn Acres furnace.
Aerodynamics permitted these furnaces to be operated without any mechanical air blast, such as a bellows. A blacksmith's bellows, for instance, would be far too small for such a task. In fact, it would have taken water wheel power and a bellows several times larger to supply such a blast.
But the air ducts are sufficient evidence to prove the Deer Creek furnaces were blown by a natural draft. Because of aerodynamic laws, air supplied by the duct increases in speed after it reaches the hearth matrix area of the furnace bowl. As it moves up through small spaces between rounded stones, air path volume is reduced. The air loses pressure and speeds up through the small passages of the hearth matrix, creating a blast of air. Even more of a blast could be gained by facing air duct entrances into the prevailing wind to gain a higher initial air speed. The Lynn furnace air duct opening was aimed to the southwest, the direction of local prevailing winds.
The only direct process furnaces in America recorded by history were either Catalan forges, small above-ground structures resembling over-sized blacksmith's forges, or larger stone tower furnaces, which might be 30 feet high. Both produced wrought iron. Other American furnaces used in the 18th and 19th centuries were indirect process stone tower furnaces, which produced cast iron pigs.
What was so mysterious about the Ohio pit iron smelters was this: Orr and I found no historic mention of them just as Mallery was also unable to find. Also, as yet I have no archaeological evidence which might conclusively identify those who constructed and operated such furnaces. However, since native Americans didn't possess iron smelting technology, the Ohio pit iron furnaces Orr and I agreed presume the furnaces were historic, dating back to the arrival of the earliest European-American pioneers in the state. We further assumed Ohio's early pioneers probably built pit smelters near where bog iron ore was easy to obtain and also, nearby the sites of early settlements and water-powered grist and sawmills. We also presumed that while these furnaces are not mentioned in Ohio history, they were overlooked as merely an adjunct to the other important activities of blacksmiths. I recognized at the time how unlikely an assumption this was, but realized that at this stage in the investigation, I needed to operate "in the safe mode," to borrow a term from Microsoft's Windows terminology.
Although we had both thermoluminescence (TL) and radiocarbon dates established for material from the Arledge mound furnace, we regard these dates as only suggestive and not as conclusive because of the disturbances caused by previous investigators. Their failure to conduct scientific excavations gives us reason for caution.
Both the TL and radiocarbon dates for the Arledge furnace fall in the middle of the 18th century, however. The TL result for Arledge, obtained from glaze on a lump of clay furnace wall, was 1740 AD, plus or minus 15 years, and from hard-baked clay, 1740 AD, plus or minus 25 years. The testing was conducted in 1992 in the TL laboratory of Professor Ralph Rowlett at the University of Missouri Anthropology Department at Columbia, Mo. The fact that this date is completely impossible, when just the science of economics alone is applied, will be fully explained in the author's book! Additional evidence will add further proof of the prehistoric presence Old World Iron Age people in Ohio.
Meanwhile, it is strange to note the same bowl-hearth matrix-air duct design was used in Europe in ancient times. In 1870 in Belgium, the remains of two natural draft pit iron furnaces were uncovered with stonework bottoms and air ducts. These furnaces were considered ancient by scholars of metallurgical history of the time of their discovery.
One such scholar, James M. Swank, secretary of the American Iron and Steel Association, mentioned the Belgian furnaces his history of iron making from ancient times through the America Colonial period, right up to the 1880s, when his history was published. Swank's history was part of his report on "The Manufacture of Iron and Steel" in the United States. This appeared in an authoritative, official U.S. government publication, a large dictionary-size volume, the "Report on the Manufactures of the U.S. at the Tenth Census" (June 1, 1880), which was published in Washington in 1883.
Swank clearly considered these Belgian furnaces to be ancient. In discussing the manufacture of iron without the use of an artificial blast in Europe at the very beginning of "the Christian era," Swank described the Belgian furnaces:
"At Lustin, in Belgium, between Namur and Dinant, two ancient furnaces were discovered in 1820, on the top of a hill, with iron yet remaining in them. They consisted of simple oval excavations with rounded bottoms in a bed of clay, 12 feet long and 9 feet wide with depth in the middle of about three feet, the top being level with the surface of the surrounding soil. A channel excavated in the clay, but covered over with stones, conducted the wind into the lower portion of each furnace. The opening of this channel was turned in the direction of the prevailing wind, so that iron could only have been made on windy days. These bloomaries contained lumps of crude wrought iron."
It is amazing to note that Swank could almost be describing the Lynn Acres furnace the APGS excavated in 1992-93! How did this technology span a 2,000-year gap from ancient Belgium to show up again in our 1992 excavation in Ohio? Was it re-invented by someone? (The depth of the Belgian furnaces seems too shallow, but over several thousand years erosion or plowing could have removed the upper portions of the oval pits.)
Equally mysterious, cast iron bars were found in some of the Deer Creek type furnaces. It is clear these furnaces were made to smelt iron from ore by the direct process, so why are the seemingly useless cast iron bars sometimes found? Were they made by accident when these furnaces got too hot?
The number (more than 30) of the Deer Creek type sites also poses a mystery, unless they are in fact the remains of the iron-production efforts of Ohio's earliest settlers. But history records no such thing. For instance, there is no mention in Swank's lengthy history of America iron making of pit iron furnaces being used at all. Instead, he limits the use of pit furnaces in more recent times to what we today call "Third World" Asian and African nations.
The Catalan forge was used in Europe in both ancient and modern times and also in early America to produce small yields of hundreds of pounds (as compared to the thousands of pounds of iron produced by the larger stone chimney furnaces of the same period in America).
A history of iron making in Ohio also is included in Swank's 1883 report, and he notes Ohio's first iron furnace was the "Hopewell" built in 1803 in Mahoning County not far from the Ohio-Pennsylvania boundary. This was a stone chimney blast furnace used to make 2.5 to 3 tons of cast iron daily, a giant compared to the Deer Creek type pit furnaces.
Those who wish to look further into this mystery might find my site database interesting:
Ohio Archaeo-Pyrogenic Sites Database
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