Eric,
This thread began, and has mostly developed, around that Michigan (with some from Wisconsin and Minnesota) native copper, more specifically its use in the upper Great Lakes area.
Yuri has begun a thread about copper casting outside of this area. Perhaps that would be a better venue for this more general discussion of ancient copper.
Tom McDonald
Much has been bandied about concerning the purity of the copper from the UP, but you must realize that the same geological process that separates the copper also separates several other metals at the same time. It does not place them miles apart but leaves the next to each other, fractions of a millimeter apart. for some clarification we will define some vocabulary.
Native copper This is copper that was left in it's metallic state by the process that concentrated it. It can be loose, or they can be stuck in a hunk of matrix exactly as they came out of the ground with other native metals in close proximity. Drift copper This is native copper that has been pounded from its matrix by glacial action. Placer deposit This is a deposit of native metal that has been removed from it's matrix by erosion (glacial or otherwise) moved from it's original location (usually by wind or water) and, by nature of its specific gravity and it's resistance to the motive force has been concentrate with other bits of metal with like characteristics.
The native copper of the UP is unusually pure. This does not, however, mean that every piece of rock with copper in it contains only copper.
Below is snip from a site about gold mining in the UP.
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In June the following year(1846), Houghton?s younger brother Jacob, found a vein of native copper on the Keweenaw Peninsula which held a small amount of gold. An assay yielded 10.25 ounces of copper, 1.75 ounces of silver and 12 grains of gold from the 28-ounce specimen
You can see that this particular sample was nearly 15% silver!
Drift copper has had most of the other materials removed by mechanical action and is usually very pure.
The specific gravities of silver, copper etc. are actually quite close when compared to sand and placer deposits may contain these in any mix.
Now as to melting.
These native metals are melted for one of three basic reasons.
One, to change it's shape to a finished product Even today, casting generally produces products that are inferior to wrought. It is only used when the form cannot economically be produced any other way, It is fairly difficult with pure copper, and frankly, if you found a 3 lb hunk of drift copper you would be better off pounding it to shape.
Two, to amalgamate several smaller pieces into one or more larger ones. The purpose of this is not ,necessarily, to produce a finished product, but to produce an ingot . Despite copper's casting difficulties, we have managed to pour ingots of it for almost as long as we have worked metals. The beauty of the ingot is that if you make it big enough, you can cut off the bad parts, melt them into the next ingot and pound the rest into whatever you want. However, since parent metal is no longer a single nugget of pure copper, the purity of the casting can be anything.
Three, to separate the metals from the matrix. This too produces a fine ingot and in the case of Mr. Houghton's sample, one with 15% silver .
Paul K. DIckman
The quote is a procedure for smelting chalcopyrite ore. That's a very different procedure from what is required to process pure native copper. Apples and oranges.
A fully engulfed large building, or a forest fire, can produce sufficient natural draft to reach copper melting temperature, but you'd need a forced draft for a simple bed of charcoal. For doing very small amounts of metal, such as small silver jewelry items, blowpipes would suffice, but for doing anything on the order of the size of the artifacts we've been examining, a bellows or blower would be required, and a *lot* of charcoal.
Let me propose that you conduct an experiment. Go to your local "high end" audio shop and purchase some oxygen free copper "monster" wire (similar properties to native copper). Now try to melt it in your backyard barbeque. The insulation will burn off, but I'll be very surprised if you can get the wire to melt without a forced air draft and *several* loads of charcoal.
Making charcoal is an industrial enterprise in itself. I'm asking is there any evidence of such activity in the area under discussion? So far I have seen no reference to such activities. Nor have I seen any reference to coal mining activity in the area. All that has been reported is mining of native copper deposits.
Meteoric copper? Perhaps you're thinking of iron. The copper we're discussing is native copper. Native copper is the result of a natural geochemical leaching process in certain types of rock formations. It results in extremely high purity copper.
True, there are impure ores present in the region as well. But there is absolutely no evidence that any of it was mined or processed prior to the latter part of the 19th century. Further, the impure ores which are present contain iron and sulphur as their major contaminants. Those impurities are extremely undesireable in copper that is to be cast. The ore has to be smelted to remove those impurities.
No significant amounts of tin, zinc, arsenic, or lead, which would improve casting qualities, are present in the ores of the region. So even if the ancients had adulterated their native copper with these ores, the result would not be an improvement in the ability to cast objects from the resultant mixture.
The ancients lacked a scientific understanding of metallurgy, but they weren't stupid. They proceded by a sequence of trial and error steps. If they added something, and the result was worse, they'd quickly understand not to do that again. Since the Native Americans in Michigan already had access to very high purity native copper, and any local adulterant they added would only make its properties worse, I'd suggest that they quickly learned not to add any adulterants.
Now the situation was different in the Old World. The metalworkers there had access to adulterants which *would* improve the casting properties of copper, and they fairly quickly learned to add such materials to their copper. That's not because they were brighter, it is simply because they had materials at hand which weren't available to the ancients of Michigan.
Gary
Paul,
I'm getting a good free education in this copper business. I thank you and Gary for your tutelage.
I don't recall reading anything about, for instance, silver artifacts in the upper Great Lakes area; but this doesn't mean it wasn't used. I rather suspect that folks were breaking rocks to extract copper, and may have discarded as debitage the non-copper bits.
I'll have to look into this, as it would seem that silver might have been present in large enough amounts that it might have wound up in archaeological contexts. And, of course, when white folks came later to investigate and further exploit some of the copper deposits, I'd be surprised if any silver were to have been ignored by them.
Tom McDonald
I don't know where you get that from. The opening sentence says very clearly "In fire-refining copper ... ".
But then that's not why I quoted the article. I did so to deal with your rebuttal of the use of a layer of coal to prevent oxidisation.
Actually I have carried out that very experiment to replicate damage seen to 'Monster cable' in a domestic fire. Just for the heck of it I through some into the base of a Jotul Alpha wood stove. The monster cable variously melted or sintered into a solid bar of copper. FYI, the Jotul Alpha is an 'air-tight' stove with the only air entry being down the face of the front door glass from the top.
That's a very different question from the use of coal to prevent oxidisation.
Its a term used to describe the copper deposited by contact with meteoric water. Meteoric water is ground water formed by precipitation. See
Only in some places.
Eric Stevens
See:
Isn't it just possible that you focus too strongly on perfect casting
- the imperfections resulting from casting may not have been a real big deal to the ancient people.
[..]
IT DOES!! It has been pointed to several times already. Your recent posting is regurgitating what you have posted before. An apparent casual visual inspection by the Museum curator, nothing more. Here is the URL again - and don't forget to scroll down a bit!!
Listen if the seriousness of your "looking" is equal to your looking on the web site - give it a miss. You wouldn't see anything anyway.
This has a good story about the Great lakes Copper deposits.
Those pictures do not show any evidence of the characteristic porosity copper casting would produce. The single large surface bubble is a blister, common when the surface of a wrought piece is overheated. Compare it to the radiograph of R666. The latter does show the characteristic deep pattern of porosity of an at least partially melted copper object.
But the imperfections due to casting pure copper *would* produce the characteristic porosity which is *not* seen in any of the pieces other than R666. As I have remarked in other posts, it is possible that this single sample may have been melted due to a cause other than deliberate casting, so by itself it is not conclusive evidence for a copper casting technology, though it is suggestive.
In any event, none of the other objects show the porosity signature of atmospheric casting. So even if the ancient people found flawed castings acceptable (and such castings would be weak and brittle), the lack of porosity is strong evidence that none of these particular items, with the possible exception of R666, were cast.
Gary
Seppo,
As Gary has pointed out, only the item R666 (site report artifact number), 55786 (Milwaukee Public Museum designation) shows the characteristic porosity of melted copper; the other copper artifacts on that page do not. My purpose in mentioning Alex Barker's observation was merely to have an eye witness to the artifact in question, to verify that it indeed does look like a lump of accidentally melted or discarded copper, as opposed to something that might have been, for instance, trimmed off the cast after cooling. The other relevant facts about it seem to have been adequately presented on Connor's web site.
So far, at least as presented on this ng, the only copper artifact that was certainly the result of melting is R666/55786. The other artifacts Mallery (and Connor) seem to think were cast either weren't, or don't have sufficient diagnostic information presented to decide.
Tom McDonald
Seppo,
Thank you for the urls.
From the second link:
"Michigan?s copper deposits were remarkable for their quality and purity. Bands of native copper were contained in outcrops 2 to 8 miles wide and of varying depth. The surface deposits first attracted the notice of Native Americans who dug out the easily accessible chunks and fashioned copper tools and adornments from them."
So mining appears to have *begun* where copper deposits were on the surface. This makes sense, as there was also drift copper (over a wider area than just the UP mining areas), and folks early on seem to have selectively used lumps of copper that needed no processing. While this might not have been an every day event, it clearly was common enough to produce many of the copper artifacts in the region.
As to mining the copper:
"They [Indians] dug pits in the ground and separated the copper from the stone by hammering, by the use of wedges, and, possibly, by the use of heat. Thousands of hammers have been found in and about the old pits."
It seems that these folks picked the visible copper out of the debitage after beating the bejesus out of the rock. That seems reasonable to me, as there seems to have been quite enough such copper available to make other methods of extraction unnecessary.
The dilemma you refer to does not seem to exist. Indian people developed the technology they needed to extract the resource they wanted. They may have developed copper casting technology as well. Since smelting wasn't necessary, casting would have been a stand-alone technology. It wasn't beyond the capacity of the Indians of the upper Great Lakes; but it also wasn't necessary.
Tom McDonald
You're missing my point. Given that casting pure copper is difficult and produces an inferior product, the casting of copper, simply to save you time forging, is a fool's errand.( Any craftsman worth his salt would figure this out by the third try. ) The only good reasons for doing it, are to make a bigger piece of copper or to clean the rock out.
Eventually, either of these tasks would lead to noticeable alloying.
I would expect this to show up in a full assay of the artifacts.
I've tried to follow this thread, (well, I wandered off when it turned into a shouting match) and I've yet to see anything that says that all the artifacts are 99+% pure copper or , in fact, that any were. I am sure that some testing must have been done, but I am a metalsmith not an anthropologist, and the relevant research has eluded me so, I have been unable to ascertain this one way or the other.
Paul K. Dickman
Paul,
Sorry. I got your point, but went off on my own tangent in my reply. I have gotten the idea that casting copper of the purity found in the UP mines and drift copper redeposited by glaciers is, as you put it, a fool's errand when forging was well known and widely practiced.
Your question about the purity of the copper in the artifacts is interesting. For my part, most of my sources tend to take it as a given that the copper artifacts in the upper Great Lakes area were nearly pure copper. I know that I've read articles that nail this down, and I'll try to get hold of some of them.
A kind person posted these links to articles in the Central States Archaeological Journal. You might find them interesting as they describe a series of experiments by one Joseph Neubauer, Sr., designed to see how the copper artifacts observed in the UP of Michigan could have been made. The first link is to an article discussing the characteristics of the material he used. The second is to a general introduction to the Neubauer experiments, and a step-by-step discussion of his process. The third is an overview and summary of the Neubauer Process. I'm not a metalworker, but ISTM that most of the information needed to replicate this Neubauer Process, and by extension the general method known to have been used by the ancient Indians of the area, may be found in these articles.
"Many pieces of copper obtained from burial mounds and from aboriginal camp sites have been chemically analyzed, with no trace of any tempering agent ever reported. In fact, the analyses prove conclusively that the copper in all the specimens examined is native copper, such as is obtainable without smelting at certain places in North America today, and that the aboriginal inhabitants were ignorant of the process of recovering copper from copper ores or of tempering or hardening by alloying copper with other metals."
I'll keep looking, however I have yet to come across any good evidence that the copper artifacts in the upper Great Lakes region were made from anything but the ca. 99.75+% pure copper, with occasional incidental inclusions of very small amounts of other materials.
Hope that is helpful.
Tom McDonald
The important point of Paul's excellent post is that if you find silver *inclusions* in the artifacts, you know that the copper was never melted (because the melting point of silver is below that of copper, and the inclusion wouldn't exist if the copper had been heated to melting).
The Neubauer articles you posted show these silver inclusions in both ancient and newly made copper tools wrought from Michigan native copper (also shown are the blisters produced by annealing and pounding which Conner incorrectly claims are evidence of casting).
OTOH, Paul is also telling us that if chemical analysis were to show an actual silver-copper alloy of uniform composition throughout an artifact, you could then reasonably conclude that it had been molten at some point.
I should note that the 15% silver assay Paul mentioned is not the same thing as saying you have a 15% alloy. Assay doesn't differentiate between inclusions and alloys. So don't be led astray by that.
If the object is high purity copper (less than 0.5% alloy), doesn't show characteristic porosity, and/or has silver inclusions, then you can be very certain it was never melted and never cast. That appears to be descriptive of all but one of the artifacts brought into evidence.
OTOH, if chemical analysis of the object were to show it is a true alloy of copper and other metals (mainly silver for Michigan native copper), and there is characteristic porosity (because silver is not an effective deoxidant for copper), then you can be confident that it has been melted in atmosphere.
Now that's *suggestive* that it may also have been cast, but as Paul notes, it may merely have been consolidated into an ingot which was then wrought into the artifact you're examining. And as I've noted, the melting of the particular artifact which does show characteristic porosity could have been accidental.
The Neubauer articles provide testimony of large amounts of small pieces of copper debris, like that produced when smithing copper in the Neubauer manner, found at native work sites which would only be there if they were *not* systematically melting and consolidating small pieces of copper. So even ingot production seems unlikely.
The more I look at this, the more the evidence piles up that the Michigan works did not involve casting of copper. Rather, the evidence, taken together, strongly indicates the Native Americans wrought native copper in ways likely to be similar to those used by Neubauer rather than casting them as some would like to claim.
The reasons I can draw that conclusion are that the artifacts appear to be mostly pure copper with little or no evidence of alloying, there are silver inclusions in some of the artifacts which is proof positive that they haven't been melted, some have blisters indicative of zealous annealing and pounding rather than melting, and there has only been one artifact shown to have the characteristic porosity caused by atmospheric melting, and that one may have been the result of an accidental exposure at some point to temperatures in excess of 1877F (a forest fire is a scenario I suggested to produce that high temperature).
One further point. *If* casting technology were being used, we'd expect to find numbers of identical artifacts, since that's what casting in molds produces. But in fact we don't find numbers of identical artifacts. We find artifacts of the same *style*, but differing in dimensions.
Neubauer says, correctly, that's a result of the necessity of following the copper when working it. In other words, the size and composition of any particular chunk of native copper dictates how much you can move and shape the metal, so it decides what sort and size of tool you can make from it.
I'd also like to reiterate something else Paul implied. The apparent fact that the Native Americans *didn't* cast native copper is an indication that they were intelligent and economical craftsmen. If they had tried casting, they would have quickly discovered it was an inferior method of utilizing the abundant raw materials available to them to produce a final product.
They weren't forced to deal with poor ores, they had abundant chunks of native copper of the appropriate sizes to smith anything they wished, and had no need to salvage small scraps. They could simply "high grade" the sites. So the intelligent thing to do would have been to work the way they apparently did, smithing instead of founding.
Gary
As that article notes, 14 billion pounds of copper have been removed from the area since the ancients were working copper there. Let the enormity of that number sink in. There was an *awful lot* of copper there in ancient times, much of it easily accessible from the surface.
Note also, as Neubauer does, that they didn't want "huge lumps". Copper is difficult to cut with primitive tools (isn't all that much fun with modern steel chisels). Neubauer suggests that the ancients would want to start with a piece of about the right size for the object they wanted to make. At most that would be a lump weighing a few pounds, in the vast majority of cases it would be a lump smaller than a hen's egg. Even today, such lumps are relatively plentiful in the copper belt. They were vastly more so 6,000 years ago before modern industrial man started extracting copper from the region.
Gary
We did come up with the idea that you might get this sort of temperature in a funeral pyre, because you need that sort of temperature to turn the body to ash.
Martyn,
I now think that it's unlikely that the melted bit was from a cremation, although it's not impossible. It wasn't found in a burial context, for one thing.
For another, at least one study of cremations at the Riverside site appear to indicate that the typical cremation fire was either not hot enough, or not maintained long enough, to fully reduce all of the bones. Since cremation temperatures are typically well below the melting point of copper (by over 300 degrees F, in several references), that scenario seems less likely that I first thought. I'd go with Gary on this one, especially as the occupation was aceramic.
If you are interested in following up on this, there is an article entitled, 'Analysis of a Cremated Burial from the Riverside Cemetery, Menominee County, Michigan', pp. 383-389, _An Archaeological Perspective_, 1972, Lewis Binford. Seminar Press, London. The article prior to that one is a comparative study of three other Michigan Late Archaic (Red Ocher) cemeteries, comparing a total of eight burials.
Note: some burials, as with the Riverside burial in the noted article, include more than one individual. The Riverside burial included a MNI of 4, three adults and a child.
Tom McDonald
This is a "fact" only if you disregard all evidence to the contrary, as you appear to be doing.
Yuri.
Yuri Kuchinsky -=O=-
Not everything that is possible is probable.
Wishing won't make it so.
Yuri.
Yuri Kuchinsky -=O=-
My main point here is that Gary Coffman is wrong with his speculations that copper casting was too difficult for ancient peoples to do.
I'm merely trying to teach Mr. Coffman a few things about metalworking, as it applies to ancient peoples.
Yuri.
Yuri Kuchinsky -=O=-
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