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Day 74 (11.14.07) - Cornwall Iron Furnace

Again, I gave up on Philly. We learn how iron was smelted, cast and forged in Cornwall, PA from 1742 - 1883.

overcast 55 °F


Miles Driven - 38
Weather - Cool, but decent (mid 50's)
Camped - Lancaster, PA Walmart (No, I am NOT driving up to Hershey again!)


I set the alarm last night so we would be ready at 8 AM when the rental car place opened. By 8:15 we hadn't heard from them so I called. Sure, they could get us a car today, but by 4 PM and the price was $10 higher then what they quoted me when I made the reservation the night before. Maybe my skin is just too thin, but I had a problem with this change in time & price and told them to forget it. So again, no Philly.

We hung around the campground for awhile to catch up on laundry and other chores, then decided we still had time to head at least a little bit south today. Shortly after we left, Mom spotted a red tailed hawk - since this was her find, she wanted me to upload this even though the picture wasn't that great. I shouldn't complain though, it's probably a good sign that we still find interest in such things after 2 1/2 months on the road.


A few miles farther we saw a brown sign for Cornwall Furnace (brown usually meaning a point of interest, park, museum, or such). We didn't have any information about this but I thought it sounded interesting and turned off. When we got to Cornwall, we found a really cool gothic looking building that said it was the "Cornwall Iron Furnance" museum. The furnace itself is about in the middle (where the Chimney is). It was 'fed' from the upper floor of the building on the left, and molten iron used for molds or 'pig iron' in the molding room at the bottom floor of the building on the right.


The visitors center had a really nice interpretive area with displays about the history of the iron furnace, how it worked and types of products it made. You could also take a tour of the furnace itself as well as some of the support structure. Unfortunately there were too many steps for Mom, but she was able to watch an introductory film and go through the interpretive displays, which had all the essential information. I also took the tour and bought a book in the gift shop, so she didn't miss very much - except Fred, my tour guide.


I think it would be easier to understand all this if I mix up the information from the Interpretive displays and the furnace tour, and just present the iron making story from Cornwall.

Iron making itself dates back to the late bronze age. There is a great deal of debate, but most evidence points to the Hittites developing the first smelting process to reduce iron ore into workable iron. The iron in iron ore,is bound up in molecules with oxygen. Smelting is a process where carbon is used to break up the Iron Oxide molecules into separate Iron and Carbon Dioxide molecules. (Smelting is used for other metal ores as well, but this discussion is about Iron, so I'll ignore those). When iron smelting was first developed, people couldn't heat the ores high enough to actually melt iron, so they used a furnace called a 'bloomery'. This worked and continued to be used to make wrought iron until the middle ages, but it didn't produce very much iron for all the effort.

Even bloomeries needed a higher temperature then could be created by a wood fire alone, so used charcoal and air bellows to increase the heat produced by the charcoal. As demand for iron grew during the middle ages, people began to build bigger and bigger furnaces and develop techniques to increase production. Waterwheels were introduced to pump larger bellows needed for bigger furnaces. Some of the large bloomery furnaces probably started getting hot enough to actually melt the iron ore and there was probably a gradual shift to blast furnaces as the benefits became apparent. The first written record of a blast furnace (one that produced molten iron intentionally) was in 1340 in Belgiam.

So most of the early middle ages, Bloomeries could produce only about 15 kg of iron per firing, and firings were not continuous. The later ones brought that output up to about 300 kg, but still wasn't a lot of output for the effort. The Cornwall blast furnace produced about 2 tons of iron per tap (twice a day), quite an improvement over bloomery outputs. By 1883 it was obsolete however as coal burning 'hot' blast furnaces required none of the forest chopping/charcoal making effort and produced about 5 times as much iron. (100 tons/week vs 20 tons/week).

Early immigrants to America bought iron from England, but this was slow and very expensive and probably couldn't meet the demand of a rapidly growing population. So the early colonists had a pretty big incentive to look for their own sources for iron (also some immigrants probably brought iron working knowledge & skill over with them). The first successful iron works was built in Saugus, Massachussets in 1646. By the 1730's, there were already six iron furnaces in Pennsylvania when a man named Peter Grubb moved to the Cornwall area. He was a stonemason, but recognized good iron ore outcroppings next to his property. Shortly after, he acquired that property and by 1742 has built the furnace at Cornwall.

Over the years, this developed into a small, self contained community (company town).

A cadre of workers chopped wood, then colliers converted it to charcoal needed by the furnace. 340 acres of wood were needed per year.

Molders used clay to prepare molds for cast iron products. They were amoung the most skilled workers, but were only paid for the good pieces they produced.

The founder was in charge of the whole operation, he determined the proper amounts of ore, limestone and charcoal to load into the furnace, controlled how much air blast was used and when to tap the molten iron.

Minors dug the ore in an open pit mine. Although the furnace was closed in 1883, the mine continued in operation until 1952, and again as an underground mine until 1973 when it was flooded by Hurricane Agnes. (The mine was fairly well spent by then, so engineers advised against the cost of pumping it out and reopening it). During 234 years of operation, the Cornwall mine produced 106 million tons of iron ore. The type of ore found in Cornwall was Magnitite (FE3-O4), also called Lodestone.


The top of the furnace (Tunnel Head) is 31' from the floor and 17" wide. It gradually widens to a maximum of about 9' (the Bosh), then narrows again to about 4 ' at the bottom (or Crucible). The walls were as much as 9' thick at the base, so the entire furnace was about 28' wide on each side.

Of course, the tour couldn't take me into the inside of the furnace, so a diagram may prove useful. Throughout the day, loads of iron ore, limestone and charcoal and shoveled into the top (tunnel head). As these make there way down, the charcoal burns hotter and hotter until the ore starts to melt. Air is pumped into the furnace from three sides (the dark line leading to the bottom of the furnace from the left - the final tube is called the Tuyere.


Limestone is used to bind to impurities in the molten iron and settles to the bottom as slag. Slag is lighter then the molten iron, so can be poured off first and separated from the more pure iron.

Carbon from the burning coal binds to the oxygen in the iron ore and escapes out the chimney as carbon dioxide (CO2).

This type of furnace was kept running 24 hours a day, 7 days a week, for most of the year. It took two days to restart it, so this isn't something you'd want to put out any more often then necessary. During the first hundred years or so when the water wheel was used to provide the blast (air pumped into the furnace), the furnace was only shut down when the creek froze in the winter for about three months. Any maintenance work was done to the furnace then (relining the inner brick walls for example). In the 1840's, a steam engine replaced water for pumping air, so the furnace only had to be shut down for about a month for maintenance.

Also, around 1800, the bellows were replaced with blowing tubes. These look like big water tanks, but used a piston to pump air through a duct system into the furnace. There were two tanks, one on each side of a giant water wheel, so air would always be pumping. (I thought this shot showed the wooden blowing tubes, but it just shows the wheel & giant axel that drove the tubes. My pictures from the tour didn't come out as good as I'd like)


So we visited the tunnel head and saw where charcoal, limestone, and iron ore was dumped into the furnace. Then we climbed down to the wheel and blowing tubes pumped air into the furnace, so the main section left was the bottom of the furnace (hearth) where the final product was tapped. Twice a day, when the iron was ready, a clay dam stone would be removed and first the slag run off. Then another clay block removed and the molten ore poured out.

Some ore was collected in ladles and poured into prepared clay molds. The Cornwall furnace produced iron plates for stoves as well as cast cooking pots and pans. Here is a picture of the hearth, with a couple of molds ready for pouring (there was some scaffolding on the right side, so this is showing only part of the front view).


This was called a 'Ten Plate Stove', since molds were made of ten separate plates, then assembled to make the stove:


Also, molten iron ran down ditches that had been previously formed in the floor of the furnace room (molding room) and into slots molded from pieces of wood. Early iron workers thought this arrangements looked like baby piglets sucking from the mother sow, so these bars were called 'Pig Iron' and the name stuck.


Pig iron was the main product produced by the Cornwall furnace. This wasn't very useful by itself, but was the major product required for other iron work by forges and foundries. Cornwall was also a fully integrated iron works, so did produce cast iron products and also bar iron from a forge, but also sold pig iron to other foundaries and forges. In 1865, a 100 pound bar of pig iron was valued at $2.

The differences between the types of iron works are then:

The blast furnace, which produces molten iron, 'Pig Iron' - or the raw iron product after smelting.

The foundary, which produces cast iron products. Many furnace operators also ran a foundry at the same location.

The forge, which converted the cast iron (primarly 'pigs') into stronger wrought iron.

The iron formed from smelting is hard and brittle. It can be useful for objects which need to withstand a lot of heat but don't have to take much of a pounding, which would crack them. If cast iron is pounded, it realigns the iron molecules and strenthens them. It also removes even more impurities. Wrought iron (usually in bar form) was the product needed by blacksmiths to make horseshoes, farm implements, hinges, door and window latches. Bar iron could also be run through a rolling mill and converted into nails.

By the late middle ages, Europe had developed a water driven Trip Hammer, which could forge much larger quantities of pig iron into wrought iron then could be done manually. Here is an illustration of a trip hammer in use in England. The bright glowing object is a piece of pig iron that has been heated red hot, then is being pounded by the trip hammer as the water wheel alternately raises and drops it.


This very similar trip hammer was in use in PA near Caldwell. It is probably the only wooden trip hammer left in existance in the western hemisphere. The large hammer head would be on the left, but is not attached.


I never quite understood why ore had to be 'smelted' before, or what the big deal was with the 'iron age', so this was all very educational for me. It was also interesting to note how much wood had to be converted to charcoal to smelt iron so that by the time the American colonies were getting started, most of Britian's forests were gone and it and needed American pig iron to keep it's forges working. This was why the English Parlement passed laws requiring raw pig iron to be shipped to England for processing. However the colonists also needed wrought iron products and it certainly was not cost effective to ship the pig iron to England then have to buy the finished iron products back at much higher prices. Hmm, it's interesting how all this starts to fit together...

So, having spent most of the morning doing chores and most of the afternoon learning how iron was made, we didn't have much time left. We did pass this beautiful United Methodist Church in Cornwall on our way out of town - loved the way they mixed stone and brickwork in the same building.


However, it was too late to do much else. We did have time to stop in Lancaster, learn where the best places were to learn about the Amish (on tap for tomorrow), and find a Wal-mart to stay in. (We were still close enough to Hershey to go back to the nice RV campground, but I think emotionally we needed to feel like we were moving south - even if it wasn't very far.)

Posted by jl98584 15:45 Archived in USA Tagged family_travel

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