Copper Casting In Ancient America



Maybe you saw some other data but what I saw was a *single* blurry x-ray photo, with a *single* blurry white dot in it. I was supremely unimpressed with that, so much so that I would say it wasn't a gun and it sure wasn't smoking.
But maybe there were other x-ray photos?
Jim
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The picture of the adze head had clusters of bubbles, quite characteristic of casting (or poor arc welding).
Gary
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Gary Coffman wrote:
<snip>

Gary,
    On what do you base this? Are you aware of the distances that this copper was traded in North America? We're not just talking about northern Wisconsin and the UP of Michigan.
    The extraction took place over more than 5000 years, albeit there were some periods (e.g.: ca. 3000 to 1000 BC) in which the copper seems to have been more intensively used.

    What about an unsystematic trade? For most of the time, there does not seem to have been long-distance trade; but things were traded between contiguous populations over thousands of miles. Late in pre-Columbian times, there were a couple of cultures that may have had longer-distance trade; but even that seems to have involved middlemen at various points rather than direct trade from the source to the end-users.
Everything I've read recently seems to say that

    That's true. There was for certain some contact around 1000 AD, including at least one short-term (>10 years) Norse occupation in Newfoundland. There were undoubtedly other visits by the Norse to other parts of coastal North America. There might have been some Norse travel beyond that; but that hasn't been established. Work continues that might reveal more contacts.
    That's my view. Unless you've got a stomach for lots of crap, I'd suggest you tip-toe away quietly from this particular line of thought. YMMV.     

    I've been wondering this for a while. Are there any other ways in which such voids might occur in copper without melting the copper? For instance, might linear voids occur if the copper were folded and hammered together, or if a couple of separate pieces were hammered into one piece?
    Also, are there any other ways for bubbles to occur in copper artifacts without casting? The Native Americans were known to have worked copper while it was hot (I've heard up to 800 C); would this have any effect on voids or bubbles?

    Can that be turned around a bit, to say that if porosity exists in a very small percentage of copper artifacts that may have been cast, this would indicate a fair degree of sophistication in casting copper?
Tom McDonald
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On Sun, 30 May 2004 13:32:25 -0500, Tom McDonald

http://www.minsocam.org/MSA/collectors_corner/vft/mi2c.htm is a site giving the background to the formation of the Michigan deposits.

Eric Stevens
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Eric Stevens wrote:

That site is probably the most extensive one available on the Great Lakes copper deposits. Unfortunately it loads terribly slowly. This page adresses the topic of this thread directly: http://www.minsocam.org/MSA/collectors_corner/vft/mi3a.htm
Quote: "The natives used the copper to create projectile points ( spear points, arrowheads, harpoons), cutting tools, chisels, knives, celts, axes, wedges, awls, fishhooks, gaffs and ornaments ( beads, bracelets, gorgets small breast plates). They would hammer the copper into sheets and then form the tools. The hammering would work harden the copper so a heating in the fire allowed the metal to anneal and remove the dislocations that cause brittleness. They would grind the cutting edges to sharpen them. There is no evidence that they melted the copper and poured it into molds. The copper was already a pure native metal so that they did not have to heat ore up and smelt it from copper compounds."
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This also appears to be how they made the copper comals in Oaxaca.
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wrote:

I don't insist that there be no middlemen. Even modern trade is often conducted via middlemen. What I am suggesting by saying the trade was likely systematic is that it wasn't just a matter of happenstance that items were traded. I suspect that to move the quantities involved beyond the local area, a more deliberate system of trading would have been required.

Pre-Columbian visits to the New World aren't something I know much about, for sure. But the little I've read about it seems to say that the Norse weren't the only ones involved, nor were the contacts limited to just North America. Anyway, that's not the purpose of this post, or as far as I can tell, this thread. So I'm willing to leave it at that.

Linear voids are characteristic of incomplete forging. But the radiograph of the hand adze referenced showed clusters of bubbles. I know of no way to produce that other than by casting or arc welding.

Hot work will tend to close voids. It won't produce bubbles.

I don't think that's a fair statement. Absence of a fault doesn't prove much unless you already know the item was cast. However, if you could show by other means that the item was cast, then the lack of faults would be an indication of casting sophistication.
Gary
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Gary Coffman wrote:

<snip>
Gary,
    Thanks for clearing that up. If I understand you correctly, you think finding linear voids in worked copper artifacts, one cannot assume that those artifacts were cast.
    OTOH, finding bubbles is, to your knowledge, indicative of the artifact having been cast from molten metal. I noticed you said, "I know of no way..." rather than "Only casting or arc welding will produce" wrt bubbles. Is this just normal caution, or do you feel unable to make a categorical statement here? If the latter, do you know who or where one might go to get more complete and up-to-date information?
    I hope you don't take offense by my asking this; but this is fairly important to me, and I'd like to get as complete an answer as I can.

    Yeah, didn't think so.

    Thanks. If some of the copper artifacts we're discussing are found to have been cast by Indians, I'd like to think the Indians who made them had developed sophistication in the process.
Tom McDonald
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wrote:

Correct. Linear voids aren't porosity in the usual sense.

I was trying to be careful in my language. There may well be more exotic ways to generate internal bubbles in copper than atmospheric casting or arc welding. But I'm confident the statement is accurate in the context of this discussion.
Please note, however, that I am not a metallurgist by trade. I do have some training, and some experience working copper, but if you require a credentialed opinion, then I'd suggest consulting a metallurgist working for one of the large copper mining or fabricating companies.

I'd be very surprised if the Native Americans would have had much success producing porosity free castings using the simple casting methods likely to have been available to them.
Modern industry finds it difficult. They use chemical-electrolytic methods to get void free copper. High pressure casting machines, and the use of inert gas shielding, are other methods employed to produce nearly porosity free copper objects. Those methods should have been out of reach of Native Americans of the era under discussion.
For that reason, I'd consider porosity the "smoking gun" for ancient cast copper artifacts. Primitive essentially pure copper castings *should* have porosity, so if it isn't there, then the object very likely wasn't cast.
(Note that the presence of significant alloying elements can change this statement dramatically, but isn't relevant for the nearly pure native copper under discussion.)
Please note that I'm am not saying that they couldn't have produced *serviceable* castings. A little porosity won't ruin most castings. It is just something you *expect* to find in cast copper objects, even modern ones. Usually, it is harmless, but it will almost always show up on an X-ray.
Gary
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Gary Coffman wrote:

The URL cited in the beginning of this thread http://www.iwaynet.net/~wdc/copper.htm refers to E.J. Neiburger as the main proponent for prehistoric NA copper casting. A recent paper by Neiburger with his arguments on this can be found at http://www.csasi.org/2002_july_journal/pg-144-146.htm . From the contents of the following issues there does not seemed to have been a reply, but two issues later there is a paper on a possible process for the manufacture of sophisticated copper tools without using casting, see http://www.csasi.org/2003_spring_journal/red_metal_poundings.htm with two followup papers linked at the bottom.
Very interestingly (at least to this amateur) the process proposed seems to produce the kind of bubbles Neiburger takes as proof of casting. Thus bubbles are not necessarily the "smoking gun" of casting.
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Gary Coffman wrote:

Gary,
    Erik Hammerstad has found a couple of articles about a fellow who seems to have reproduced the bubbles found in some of the copper artifacts we've been discussing, but has done it without smelting, melting or casting. These were preceded in an earlier number of the same journal, by an article by the fellow we've been discussing that has claimed the bubbles are definitively from casting. I'd appreciate it, if you're willing, if you would take a look at these articles and give me your opinion.
    This is the article by Dr. (dentist) Neiburger from Illinois, who claims Indians used casts for copper tools, etc.:
http://www.csasi.org/2002_july_journal/pg-144-146.htm
    These next three are about a fellow from Minnesota, Joseph Neubauer Sr. (Keep the names straight; I mis-read it once, and was confused for a moment.) The first two discuss the 'Neubauer Process' of hammering and annealing copper, and include observations about surface and interior bubbles formed without melting the copper. The third is a more practical article, with detail about how he did what he did.
http://www.csasi.org/2003_spring_journal/red_metal_poundings.htm
http://www.csasi.org/2003_summer_journal/red_metal_poundings.htm
http://www.csasi.org/2004_january_journal/the_neubauer_process.htm
    The writing in the articles isn't up to professional standards (it's an amateur archaeological journal, after all). I found myself having to re-read bits to be sure I understood what Peterson was saying in the last three articles. This concerns me; but the information is the important bit, and I'd like to get your reaction to these articles.
    I appreciate any time you're willing to put into reading and commenting on this. Thanks.
Tom McDonald
<snip>
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wrote:

Ok, I read the articles. What Neubauer has produced are what are called *blisters* in the industry. That's not the same thing as casting (or welding) porosity bubbles. Though blistering may appear on the surface of castings, other (incautious) hot work can produce it too.

The pictures in that article aren't conclusive.
However, this picture http://www.iwaynet.net/~wdc/rivlump.htm is much more conclusive. Note particularly the central cluster of bubbles. This is archetypical of formations of large porosity bubbles.
Note also the general appearance of the entire section of the piece above the 'R' superposed on the radiograph. The "coarse" appearance there is indicative of microscopic porosity due to vigorous melting in an atmospheric environment.
The irregular voids in the upper left of the photo may be blistering. They aren't characteristic enough to say exactly what they are, or how they could have gotten there.
I would love to say with absolute certainty that at least a portion of the object was subjected to vigorous melting. I can't because the apparent coarseness could be due to surface irregularities. I'd want to see the object in 3D to rule that out for sure. But the cluster of larger bubbles is a pretty strong indication that the microscopic structure is similar.
Given the fluid nature of molten copper, I'd say the piece would have to have been contained in some fashion while it was molten in order to retain significant thickness when cooled. That's a rough and ready definition of open casting.
Note that a welding repair technique called casting in place would also produce this same sort of structure if done without inert shielding gas. There's a crackerjack welding instructor who lurks here who should be able to give you a graphic demonstration of what happens when TIG welding copper, and you lose your shielding gas.
In general, if you're trying to determine if a copper item was open cast, you should be looking for *many* tiny bubbles, most microscopic, that give the interior a coarse or foamy appearance on the radiograph at low magnification. At higher magnifications, you should be able to distinguish many clusters of microscopic bubbles. A few large, and especially irregular, surface blisters won't tell the tale.
Gary
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Gary Coffman wrote:

Gary,
    As always, thanks for your reply. If nothing else, I'm learning something.
    I've emailed the curator of the anthropology collection at the Milwaukee Public Museum, where R666 is apparently located. Here is his contact information:
Alex W. Barker, Ph.D. Vice President of Collections and Research, Curator of North American Archaeology & Department Head, Anthropology Phone: (414) 278-2786 Fax: (414) 278-6100 Email: snipped-for-privacy@mpm.edu
    With luck, he or one of his associates can give me a leg up on this issue from an archaeological perspective.
Tom McDonald
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Tom McDonald wrote:

No "linear voids" were in evidence in the material you have been referred to several times. The melting point of Copper is 1083 C, not overly high - to weld via forging requires it to be close to that temperature. The melting point of Iron is 1535 C.

Tom, you are resorting to SPIN again. The "I know of no way..." said by a person who is intimately familiar with the subject is the same as saying "Only casting or arc welding will produce...". There is no difference. You are attempting to build yourself an escape clause to denial again - not on any facts but by the simple re-interpreting (spin) of words.

What has been said by Gary is the same as has been pointed to by a number of people - to published information and other expert studies that includes x-ray information etc. There is no real mystery about this. The only mystery has been your denials of it.
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On Wed, 26 May 2004 16:47:59 -0500, Tom McDonald

I accept all that. However it is not an adequate answer to the questions posed by Gunner.

Eric Stevens
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