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Ken Johnston

Archaeological slag: can someone tell me what was going on based on these artifacts?

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This looks like a job for Mark and Alan!

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Somebody request a historical archaeologist with an interest in iron? At your service! B)

 

You have discovered a blast furnace site, where charcoal was used to make cast iron. You have ore, slag, firebrick, and a bit of cast iron sprue. You didn't fill out your location so I looked up your IP, which shows you to be in eastern Ohio, is that correct? Loads of charcoal-fired blast furnace stacks in that area, mostly dating in the 1820-1870 timeframe. This website might help you: http://www.oldeforester.com/ironintr.htm.

 

Is the furnace still standing? Or did you just happen upon the slag heap out in the woods?

 

Some of these furnaces would have produced some finished castings, but most just made pig iron to use in making wrought iron and steel. There may or may not be (or have been) a finery forge nearby, this stuff was bring shipped incredible distances even way back when. For instance, pig iron made near where I live was being shipped via wagon, flatboat, and steamboat all the way to Pittsburg, PA in 1850. That's over a thousand miles by water through four states (six if you count TN twice and Ohio once), down the Watauga to the Holston and Tennessee Rivers all the way to its confluence with the Ohio in Kentucky, then upstream on the Ohio to Pittsburg.

 

Any other goodies floating around?

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Somebody request a historical archaeologist with an interest in iron? At your service! B)

 

You have discovered a blast furnace site, where charcoal was used to make cast iron. You have ore, slag, firebrick, and a bit of cast iron sprue. You didn't fill out your location so I looked up your IP, which shows you to be in eastern Ohio, is that correct? Loads of charcoal-fired blast furnace stacks in that area, mostly dating in the 1820-1870 timeframe. This website might help you: http://www.oldeforester.com/ironintr.htm.

 

Is the furnace still standing? Or did you just happen upon the slag heap out in the woods?

 

Some of these furnaces would have produced some finished castings, but most just made pig iron to use in making wrought iron and steel. There may or may not be (or have been) a finery forge nearby, this stuff was bring shipped incredible distances even way back when. For instance, pig iron made near where I live was being shipped via wagon, flatboat, and steamboat all the way to Pittsburg, PA in 1850. That's over a thousand miles by water through four states (six if you count TN twice and Ohio once), down the Watauga to the Holston and Tennessee Rivers all the way to its confluence with the Ohio in Kentucky, then upstream on the Ohio to Pittsburg.

 

Any other goodies floating around?

 

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Thank you very much Alan. Can you tell me which of the pieces is ore vs. slag? I understand the firebrick one. Also, is the green glass considered slag? The objects came from a 5ft deep trench on top of hill. These pieces are all I have found. The context is prehistoric (Paleolithic) stone tools so I was trying to determine if these can be accounted for historically. The slag was probably buried historically into this context. There is a smithery location 250 yards and 55 feet elevation below the slag find site. It was in operation during the time frame you describe.

 

An archaeologist friend of mine also found slag in a Paleolithic context and isolated some organic-bearing material in it which was carbon dated to Paleolithic times by the world's top lab for this. I took a sample from the item in the 1st photo which I thought might be charcoal and might also be radio carbon dated. It was not organic and maybe because what I thought was charcoal was actually coal. My friend is trying to get additional dates to see if his slag could be that old.

 

I think what I have is historical but I'll let you know if he gets any more very old dates. Appreciate your help, thanks for sharing your knowledge.

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Lots of furnaces in southeastern Ohio. I've been to many of the sites and so has Mr. Powers. The green glass slag is what you usually find in Ohio and Northern Kentucky. Other areas in Western Ky and Tenn. have many different colors of glass slag, from black, purple, grey, to Robin egg blue. I was curious about the different colors and had access to an x-ray spectrometer. After analyzing the different colored slags, I found they were all nearly identical in composition. so I'm not sure why the different colors.

I can't seem to post any pictures, I'll try again later.

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This location is just off the old National Road (US 40) 2 miles north of Jacksontown, Ohio, in Licking County. With all the traffic on the National Road I was puzzled why people would be smelting on what appeared to a small scale (no huge slag pile or bloomery remnants I have been able to detect.) Or maybe metal raw material along with the slag was delivered to the nearby smithery.? Or could these be products of a smithery operation? I am aware of places like Hope Furnace and Buckeye Furnace and Union Furnace and others stretching into Kentucky which were using a band of high quality ore up to a foot thick which is located just above the Vanport limestone formation. Was this stuff pictured here made in an operation as large as those? Please excuse my ignorance. I'm a stone tool guy and after running into the slag became interested in this whole area. Thanks for the information.

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I had read an article on small pit furnaces near Columbus, Oh. They were very early furnaces, maybe 1700's. It may be somewhere in the link Alan posted. I'll check my furnace map and see if it shows anything for the area you described. I stomped all over the woods near Dillon Lake just north of Zanesville, there was a furnace there in the early 1800's but I couldn't find any sign of it, only some anchors in the river for a dam they used to power the blowers and other equipment. Slag usually isn't on top of a hill, it's dumped in the steam or piled in the old ore pit, I don't know why anyone would haul it up.

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My guess would be redeposition. The glassy slag is from a blast furnace, not a bloomery or forge. Slag from bloomery/finery operations is much more foamy-looking. I can assure you it is not prehistoric. To get a date from slag you need to have thermoluminescence testing done, and that is not cheap. Not worse than AMS carbon dates, though. Around $500-$1000 a pop depending on what the lab has to do to prep it.

 

The Euro guys go nuts with slag colors, but all they mean is iron content (which relates to smelt efficiency)

, oxidation level in the furnace, and sometimes trace elements.

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Oh, and your second photo looks like ore from here. I'd have to see it in person to be sure.

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We make hundreds of pounds of slag every day (well, we melt 4-5 days per week). It all looks like the green piece you have. Our melters pull slag samples during the melt to determine how much oxygen is active in the metal and add de-oxidizers accordingly. We are melting via Electric Arc Furnace (EAF) with acidic slag. Basic slag tends to be a bit bluer, and I think this is due to the extra calcium (lime) added. Ours is just in the green--->black spectrum. All induction melting I have seen makes black slag, but we don't inject oxygen for that.

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http://s183.photobucket.com/user/Jammer_55/library/Iron%20furnace

 

Is there some reason I can't post the link from my photobucket? I just typed this one for the whole album. Lots of different furnaces but with very little explanation. I just love traveling to these furnace sites, I just can't tromp back through the brush like I used to. Now finding the ore source is as much fun as finding the furnace.

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