Smelter Tech: The Reverberatory Furnace

The copper that arrived to the smelter was anywhere from 70 to 90 percent pure. Due to the unique nature of Lake Superior copper, most of those impurities manifested themselves as pieces of foreign rock imbedded within the copper itself. As a result Copper Country smelters – including the Quincy Smelting Works – utilized a rather uncomplicated procedure to purify their copper wares. A process that essentially boiled down to melting the copper and skimming off its impurities. The central piece of equipment used during this process was the reverberatory furnace.

A reverberatory furnace consisted of a large brick-lined pot – known as a hearth – in which the copper was melted down to a liquid. This was done not with direct heat, but with reflected – or reverberated – heat emanating from an adjacent firebox. The natural draft created by the furnace’s chimney would pull the hot gases from the firebox up across the specially curved top of the hearth before being pulled up the flue. Along the way those hot gasses would reverberate off the roof and bounce down into the copper filled hearth – slowly melting it.

While rather simple in its aggregate, the actually reverberatory process actually involved several procedures and nearly a full day before copper could be poured into waiting ingots. The first of these steps was to load the copper into the furnace in a process known as “charging”.

During the charging process the furnace’s firebox is doused and its doors and top are opened. While copper could have been loaded into the furnace from any of these side doors, most of the mineral was loaded from the top – thanks to the furnace’s removable top. The furnace is first filled with the smaller pieces of copper to create a carpet of mineral along the furnace’s bottom. Then the larger pieces – mass copper – are placed on top of that copper carpet. After the furnace reaches is maximum load – about 36,000 pounds – its top is dropped back in place and all the doors are closed.

With the furnace charged it was now time to ignite the firebox and beginning the heating process. A layer of coal was placed in the firebox atop a metal grate spanning across the ash pit and lit on fire. The fire is fed by air drafting up through the open ash pit, air that is forced through the grate and directly across the hot coals before its drafted over to the hearth and up the flue.

The natural draft created between the flue and ash pit opening creates a constant flow of hot gasses that drift out of the firebox, up over the hearth’s roof, and finally up the flue. As mentioned before, the curved top of the hearth forces those gases to reverberate down into the copper itself facilitating its melting. During this stage the furnace is kept tightly shut to maximize the heat within the hearth.

After a few hours in the furnace, the copper and rock will begin to melt and the next step of the process can commence. Due to the differences in density between copper and the rock that surrounds it, the molten contents of the hearth began to separate naturally into two distinct layers. At the bottom is the copper itself – known as the matte – while floating on top forms a layer of molten rock known as slag. Once formed, this slag would be skimmed off the top of the copper and removed through the furnace door. Skimming would continue for another 12-15 hours until all the remaining copper is thoroughly melted and all the slag that forms is removed.

With the melting stage now complete (16 hours later) the entire smelting process is three-quarters of the way complete. Now the final refining stage begins, were the last drops of impurities are removed from the molten copper in a process known as “rabbling”. Rabbling involves agitating the copper to expose it to air and oxidize and remaining impurities within it. This is done by blowing compressed air into the molten mixture, or more traditionally by splashing the copper around using a paddle-like tool known as a rabble. This oxidizing method forces further impurities out of the copper matte and to the surface. This is done for another 1-2 hours to insure the entire matte has been oxidized, at which time the resultant slag is again skimmed off and removed.

As a result of this rabbling a great deal of the copper matte has also been oxidized, creating a copper oxide mixture. In order to remove this excess oxygen from the mix and return the copper to a more native state, the matte undergoes a final stage in the smelting process known as “poling”. Here workers insert into the molten copper several poles of wood – usually poplar – measuring between 15 and 20 feet in length. As the wood is consumed in the hot copper, it releases carbon into the mixture. This carbon attaches itself to the oxygen in the copper to form carbon oxides which are then drawn up out of the furnace through the chimney.

Here’s a shot of this poling process being performed at the C&H smelter. The “pole” here looks more like a log as its dragged into the furnace by means of an overhead crane. Several more poles can be seen stacked up in the foreground. This process would continue for sevearl hours until the majority of the copper oxide had been reduced. At this point the copper is as pure as the reverberatory furnace is going to make it and the final step can finally commence.

That final step would be the casting process itself, by which the molten copper is removed from the furnace in large ladles and then poured into rows of ingot molds. Those molds would then be dropped into a water bath to cool them before being removed and sent out to the warehouse – some 22 hours after the copper was first loaded into the furnace.

Information for this post was obtained from “The Copper Mines of Lake Superior” by Thomas Arthur Rickard (1905).

Discuss…

  1. John from the Prairie

    Ok, we have mines, railroads/trams, stamp mills, smelters, coal docks, explosive cheese factories, but where were the bricks made? I love the red sandstone buildings, but there is still oooooodles of brick to be made for building, in addition to paving stones, and in the picture above, fire bricks.

    Who made the bricks in the Copper Country?

  2. Of all my research into the region for my historic map sets I only found evidence of one brick works in the entire region – that belonging to the North Canal Brick Company up along the Portage Canal just north of Oskar. There was also an Asphalt Block and Paving Company out on the Franklin sands at Gross Point, but I can’t be sure they made bricks.

    The most common brick company I found out on my travels was a company called Brush, which I found stamped on many bricks all over the area (osceola, south kearsarge, north kearsarge, tamarack…)

    I thought perhaps mine companies were making their own bricks, but of course I have yet to find C&H’s brick factory along mine street here in Calumet….

  3. Great posts on the Quincy smelter. Very cool the site still remains. It must have been quite a contrast between the glory days of the Quincy and the last decades. Just cobble things together with the least investment. Simple return on investment, understandably, and nobody probably thought twice about it at the time. Still tough to see those early grand structures just essentially worked into the ground.

  4. As a general observation. I find early industrial landscape photos amazing. Pretty much not a tree in site. Trees were the first to go as they were a great local resource. All similiar in northern MN, WI. In this day and age, I can’t image these beautiful areas today looking so bleak but I suppose that was progress in those days and folks had a completely different perspective or expectations of the land.

  5. There’s a video put out by C&H in the 50s that you can still get that shows the smelting process. I forget the name, but know that they sell it at Quincy, Copper World, etc. Or you can be cheap like me and get if from the library.

    It also starts out in front of Centennial #3 ;)

  6. Just because Jay mentioned it, I think there’s also a video which shows the dewatering of one of the Centennial shafts — showing various levels, and what artifacts were revealed, as the water went down. Made me drool a little.

  7. Ive seen the video Jays talking about, dcclark where did you find that video?

  8. The one David’s talking about is “Unwatering the Osceola”. I’ve tried to get it from my local library via Melcat, but was unsuccessful.

    Just because your local library doesn’t have a book or video you’re looking for, they can still get it. Just use the Melcat system. I’ve gotten many books sent to my local library from the Portage Lake library in Houghton.

  9. Bricks, I found a reference to Lake Superior Stone Brick Company which was in Ripley, this was in 1913. They made a sand-lime brick, from the little reading I did, they weren’t to good for exterior surfaces.
    The other thing I did read was the clay in the UP was not good for brick making, it was to sandy if I remember right. So for good brick, the material would have had to be shipped in.

  10. I have that video of the Unwatering of Osceola, I could only imagine trying to pump that much “untreated” water out of a mine now. Down the creek, through the swamp and out into Lake Superior.
    The thing that got me was the diver they sent down into the shaft to open a water valve that would allow I believe it was Tamarack to help pump water out. Not sure if they showed that in the video, Tech has a couple of photos of it.

    http://digarch.lib.mtu.edu/showbib.aspx?bib_id=676088#

    http://digarch.lib.mtu.edu/showbib.aspx?bib_id=686582#

  11. … the first thing he did upon coming up from however many thousands of feet underwater was to have a smoke. Anyone else think that wouldn’t exactly fly nowadays? :P

  12. I did a quick Google search on “unwatering osceola video” (no quotes) and found several sites selling the DVD for under $25. Keweenawvideo.com is one of the sites that has it. They also have one called “Quality Control from Ore to Finished Product” with a C&H logo on the cover that may be the smelting video that Jay was talking about.

  13. LOL!!!

    “Thanks for risking your life by diving several thousand feet into a hole in the ground, now I’m going to have to ask you to step outside to have a smoke.”

  14. Exactly how far down was the 28th level? I cannot believe that the diver went 2800 feet !

  15. 2800 feet was probably right on the incline, although if you assume that the shaft was on a 45 degree angle (measured from vertical), then it was closer to 1900 feet in vertical depth. I assume that’s why he was in that HUGE pressure suit… no way anyone could go that deep without pressure!

  16. Then wander around in a dark tunnel looking for a water valve, not my idea of a day at work. Cough, cough, get me up, I need a smoke
    Both of those videos are good, the Quality Control one is nice since it shows a bit about the whole process

  17. Yep, that’s the one I was thinking of. Quality Control is an interesting video that shows the later C&H operations.

    Well, other than the older gentlemen yelling at you in the beginning ;)

  18. IT maybe 280 Fathoms as well… Quincy for example measure depth in Fathoms (divided by 10) below surface along the dip of the deposit. The East adit is on the 7th level, or 70 fathoms/420 feet. The 28th level at Osceola maybe 280 Fathoms or 1680 Feet along the dip. I would have to scale it off to confirm…

    The diver probably wasn’t all that deep, what happened was Osceola was connected to the C&H workings at the 28th level, and a bulkhead was erected so the Osceola workings could flood without impacting the C&H workings. Once pumping started a diferential head started to build and the valve connecting the two needed to be opened inorder to equilize the workings and not only speed the rate of dewatering but allow dewatering to safely continue (high pressure blow outs tend to suck!)

  19. As far as being some 1,500 to 2,800 feet below the ground, I would THINK that if it were not for the temperatures (and dangers) involved one could get away with a simple dry suit or wet suit today. From what I recall from WAAAAAY back in the day with physics and such, diving 2,000 feet in a lake or ocean is one thing as you are feeling the weight of the WATER above. The various mine shafts and stopes would greatly alleviate that weight or pressure?? Just a thought…. :)

  20. From my recollection, traditional lake diving in a dry- or wet-suit, most people shouldn’t go below 60 – 100 ft. Even in a mine shaft, I can’t imagine you’d get much farther!

  21. David’s right. The average sport diver is only advised to go no deeper than the 80-100 range. I was thinking about possibly getting into scuba diving last spring. That’s a rich man’s sport.

  22. I wonder if some of the water had been pumped out already before the guy was sent down, I just couldn’t imagine sending him from the surface.
    From what I remember, they had to clean the shaft as they went down, they were sliding a pump down the skip road as they went. Somewhere I saw photos of that, it may have been in the video.

  23. Did a little digging for brick manufacturers, maybe Mike can look at this web page when he gets a chance and see if the Brush name on some of these bricks look like the ones he has seen.
    If they are a like, the manufacturer was out of New York state around Buffalo.

  24. The stamps are different, but those samples listed might of been early versions. It lists Brush as beginning in the 1870’s, the earliest examples of Brush bricks I found were in hoist foundations at Osceola, which dates to the late 1870’s. Anyway Buffalo would make sense, its on the great lakes chain and would of been easy to ship up here by boat.

    By far the Brush brick is the one I find most everywhere – in fact I found some here at the smelter as well.

  25. I am not sure how deep commercial divers can go, but they use those pressure suits and breath a special mixture of gases, not just compressed air. I took SCUBA lessons, and our instructor was one of those adventurous types who happened to do commercial diving. He was describing going down on the face of a dam to look for leaks, which required going down to over 500 feet deep. He explained a process that he had perfected to be able to drink a beer down there while in his pressure suit.

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