Copper Casting In America (Trevelyan)

Gary Coffman wrote:


Thank you that were the words I was looking for those that equals or points to "melted".... and this I have no problem with.
[..]

OH no you don't! You claimed "chemical" remember - not "melted".

...as I have been suggesting - small pieces made bigger via melting....

We were talking about so called "native copper" - ie PURE copper. My pointing to inclusions of all sorts of other imperfections among the "pure copper" veins has been rejected as it tends to point to a necessity of purification via melting. Isn't this argument now supporting my earlier suggestions, previously rejected? You are now the second person to point to "melting" for the bubble to occur/form.
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Simply over annealing one time should not cause bubbles where no flaw existed. However, over annealing can play havoc with the grain size, subsequent forging can start and then enlarge a separation caused either the weakened grain structure or possibly a preexisting flaw. If gas or moisture is able to permeate this separation, heating will will cause that gas to expand, forming a blister.
The piece in question was the blade that had one single blister clearly visible on the surface as well as in the radiograph. If this piece were able to be radiographed from the side, I would bet that the blister would be lentil shaped, showing clearily that it was caused by the expansion of what had been a flat flaw.
This is not to say that the piece could not have been melted and the flaw flattened by forging, but it also doesn't conclusively prove that it was cast.

Yes, with a lot of annealing you can coax a lot out of even bad metal. but the closer the anneal is to the finished product, the softer the finished product would be.

Even at it's hardest, copper is pretty darn soft.

work
I have no idea of what purity of copper they were using. Native copper essentialy is crystalized out of a superheated and supersaturated geothermal stew. The longer it takes this stew to cool the bigger and purer the crystals are. The native copper in the UP tends to be of abnormaly high purity. This is were the casting problems come from. Were they to melt a piece of half breed with sufficient silver, there would be few problems casting it.
Paul K. Dickman
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"Paul K. Dickman" wrote:

.... or even more than one time "where no flaw existed"....

Yep, that is quite possible too - only then one would expect, under close inspection, it would show a crack to the outside. Still one more thing is required - the metal be hot enough to be quite "plastic" for it to expand and form the bubble. Which isn't a long way away from it being fully melted to a liquid form

As you have demonstrated the bubble's shape isn't a governing factor of its cause.

The problem being two fold. One the radiographed picture showing the bubble isn't large enough to see if it has any associated porosity with it. Again forging can have reduced the visibility of such as well as any telltale shape of the bubble. The only other "clue" is the text claiming "proof" of "cast". Until proven to the contrary, one would have to assume they had a better view of the radiograph and physical inspection of the artefact than we have from the web page - secondly that they have the knowledge of the effect of casting - as well as forging of cast billets.
I for one am not prepared to reject their view on the basis of the information able to be seen on the web page. Instead I would say even IF it is cast, it is insufficient evidence to claim any common practise of casting from those few artefacts without further investigation.

Yes, I though it was probably the case - here it is worth noting that the "bad" is a relative term and to the ancients it probably wasn't as "bad" as it would be to modern craftsmen.

Yep. Here again is information that isn't known or at least readily available.

But they wouldn't know that. What they would note is that the tips would break after having been bent and unbent several times. Sharpness to the point and sides of a projectile tip would probably be more important to them than the hardness.

It was mined in West Mexico, and exported to where it was used.

So I believe. I have no idea of the purity of copper from Mexico, but this is stated:
http://www.nmnh.si.edu/anthro/outreach/anthropolog/anthropolog_2004_winter.pdf "Bells of native copper were among the exotic goods excavated in Chihuahua, Mexico ......" As I understand it "native copper" is a reference to rather pure copper.

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And as I note below, they are quite wrong. It is rather obvious that they have little practical experience or knowledge about working native copper. It behaves significantly differently from other metals when melted or cast.
Your authorities are a dentist, an engineer whose expertise is with iron and steel, and one chemist (who disagrees with 4 others at his school). Frankly, not a very impressive collection of authorities on the metallurgy of native copper.

There's a huge gap between "not identical" and grossly dissimilar. The physical chemistry of atmospheric melting of pure copper isn't something you can just wave away, or class as a dispute between quoted sources. It is a physical fact. Anyone who actually works with the metal is well aware of the forms the characteristic porosity take.
The blister they're claiming as evidence of casting simply isn't an example of the characteristic porosity you get when melting copper, which always is a collection of foam-like tiny bubbles deep in the metal. It *is* an example of what happens when you anneal native copper after it has been cold worked.
Pictures of just such blisters are on the pages Tom referenced, where Neubauer used cold work and annealing to produce artifacts like those the ancients produced. In the photos, you see blisters very similar to those being claimed to be evidence of casting on work which has provably not been melted or cast.

Again, I point to the fact that they're simply wrong.
Gary
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Gary Coffman wrote:

Copper is copper no matter what part of the world it is in. ALLOYS vary from place to place. So I find it hard to accept Michigan "native copper" is much different from that here in Australia.
I would also direct your attention to this:
http://people.uncw.edu/simmonss/P6030052.JPG
There is little question this has been melted - and where are the obvious faults?

If you go to purchase a bottle of wine, which is the most important - the label on the bottle or the taste of the content? The above is pointing to the label, ignoring the content.

[..]
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wrote:

Michigan native copper is 'meteoric' copper. Australia does have some meteoric copper (see http://www.econs.ecel.uwa.edu.au/AMHA/Newslett/news21.htm ) but it is accessible in quantitities very much smaller than in NA.

Eric Stevens
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I'm fascinated by the "meteoric copper" idea.
I'm ok with the notion that elements up to Iron are formed by gradual fusion processes inside stars.
But as far as I know, that's where these fusion processes stop.
Copper isn't formed in that way.
So I can't see how a lump of space debris could reasonably be copper. It could reasonably include a *bit* of copper, but not easily *be* a copper lump. Iron yes, you certainly get lumps of iron when, e.g. a supernova goes whomp, but copper, no I don't see how that's going to happen.
So I find it enormously unlikely that a lump made predominantly of copper might end up as a meteor. Does anyone know if there is any credibility in this claim in practice?
Apparently on date Sat, 03 Jul 2004 10:44:05 +1200, Eric Stevens

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Martyn Harrison wrote:

Martyn,
    In this case, the term 'meteoric' doesn't mean 'from meteors', as it does when it's used in the phrase 'meteoric iron'. At least as it's used in archaeology.
    Eric explained it, and could do better than me; but I recall it means that the copper was precipitated out of solution that was forced closer to the surface into igneous, and IIRC sedimentary, formations.
    As I understand it, all the elements beyond iron are formed via supernovae. So, in that sense, yes; the copper we're discussing did come from elsewhere in space.
Tom McDonald

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On Sat, 03 Jul 2004 00:38:46 GMT, Martyn Harrison

You're being confused by Eric's use of an obscure term of art for geochemically processed copper originating in a water saturated subsurface environment. All that "meteoric copper" means in this context is that it was deposited geochemically from a mildly acidic aqueous fluid whose watery origin was surface precipitation (rain->meteorology->meteoric), rather than liberation of water of hydration in the deep rock.
A more complete explanation is that rainwater percolated down through faults in volcanic rock and reacted with volcanic sulphur to form a mild sulfuric acid solution. This acid solution, raised to temperatures on the order of 350C in the basement rock (and still liquid due to the high pressure there), then dissolved copper being held in more complex oxide or sulphide form in the deep rock, producing a solution of CuSO4. Over time, geologic processes forced this copper laden solution back up towards the cooler surface regions. When iron bearing rock was encountered, the reaction
CuSO4 + Fe => FeSO4 + Cu
resulted. Since copper and iron sulphates are soluble in water, they are free to move about in the rock following fissures and faults. But metallic copper isn't soluble in water, so after the reaction it is left behind to form "veins" of native copper in the rock matrix.
To go into excruciating detail on this process requires knowledge of physical chemistry, equilibrium solutions, and a good bit of geology to understand why it works as it does.
For example, I'd expect objections from the lay person that since there is iron in the deep rock too, the geochemical refining process should have redeposited the copper there. But it doesn't, because the high temperature and pressure in the deep rock shifts the equilibrium point of the reaction in an unfavorable direction for that to occur. Higher up, where temperatures and pressures are lower, the reaction can proceed to a more favorable equilibrium with respect to copper precipitation. (There are other factors too, but I'm not going to write a geochemical treatise here.)
In any event, this natural geochemical refining process means that native copper (meteoric copper) consists of veins of extremely pure crystalline copper. This is what makes native copper so desirable, it doesn't have to be smelted or further chemically refined, it merely needs to be mechanically separated from the rock through which the veins pass.
Just as veins in the body come in different sizes, so too do ore veins in a rock matrix. The vein can be hair thin, or several feet in diameter, or any size in between. That means chunks of native copper come in all sizes, allowing the ancient craftsman working at a sufficiently rich site of native copper, such as Keweenaw, to choose the size of raw material appropriate for making whatever artifact he chose.
Gary
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wrote:

Metallic copper is readily oxidized by Oxygen with dissolve clorine under acidic conditions. Forms copper chloride which is soluble in relative high concentrations. Nitrates and other acids that are also present can do similarly. The problem with Sulferic acid, the product of hydration of S03 produced by volcanism is that it is incredibly unstable, and tends to deprotonate protonating anything. This will result in the protonation of NaCl forming NaHSO4 and HCl which is capable of catalyzing the oxidation of metalic copper to copper I chloride. When this is neutralized the copper with precipitate, forming copper carbonates usually.
It is a certain Irony of chemistry that sulfate is an oxidant, but because its so stable it generally doesn't act as an oxidant, but HCL which is technically a reductant can catalyze the oxidation of metals. The reason it can do this is that metals generally form a coat of oxide on the surface that prevent the underlying layers from oxidizing, the chloride ion, In the case of copper, although sulfate can solubilize copper I and II salts, the most common metal that coats copper is calcium or other common divalent cations. This is the reason its not good to have absolutely pure water running through copper, a small amount of calcium coats the copper and protects it. However calcium carbonates and calcium/copper complexes with carbonate are completely stable in acidic chloride solutions, and once the divalent cations are stripped from the surface of the copper it is free to oxidize with oxygen free radicals that are dissolved in water. Thus if the metalic copper is exposed to s acid sulphate solution, with contaminating salts of chlorine, floride or bromine, the consequence will be the oxidation of the metal.
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wrote:

My use of the term is correct. There are all kinds of ways of forming copper deposits of all kinds of purities. The unusually high purity of the Michigan deposits is attributable to the their 'meteoric' origin.

Eric Stevens
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On Sat, 03 Jul 2004 00:38:46 GMT, Martyn Harrison
corrected this:

'meteoric copper' is copper precipitated by the action of 'meteoric water'. See http://www.webref.org/geology/m/meteoric_water.htm and http://www.ocf.berkeley.edu/~tarcuri/finalproposal.html
"After hydrofracturing, temperature gradients and increased permeability along fractures caused meteoric waters to circulate through the pluton, effectively leaching metals from the porphyry and precipitating them in hypogene, hydrothermal veins."
Apart from that, your interpretation of the term 'meteoric' as referring to wacking great lumps of copper from space is understandable but incorrect.

I hope not.
Eric Stevens
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Eric Stevens wrote:

I really hate these poncy misleading terms like "meteoric" copper and "native" copper when perfectly good clear terms are available to use like "pure", "nugget", "vein"......
Hmmmm.... does that then meant that "meteoric iron" isn't really "meteoric" or extraterrestrial at all?

Yes, this is virtually my "back yard". There has been copper mining all along the Flinders Ranges, from North to South as well as on York Peninsular (Moonta -> Wallaroo -> Kadina districts, the "copper triangle"). A few kilometres from here is a perfectly good diamond pipe as well..... only they built a town over it, and the centre of the pipe is under the local footy oval... can't disrupt the footy you know!
The fact that they are lesser quantities doesn't really alter their composition. CU is CU wherever it is, irrespective of quantities.
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wrote:

But the Michigan copper and, presumably, the Balfour meteoric copper is of an unusually high purity.

Eric Stevens
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Eric Stevens wrote:

It is indeed that.
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On Fri, 11 Jun 2004 22:57:04 GMT, snipped-for-privacy@bellsouth.net (Gary Coffman) wrote:

With respect, that is nonsense. Casting is a technique which is used to make shapes and structures which cannot be easily made any other way.

You do them a disservice to describe them as "low skilled". The work is difficult and dnagerous, and it took centuries to develop the techniques.

Which is why the people who know how to melt and cast copper use that technique rather than straight smith-work.

I think you are missing the point, and so too may be the art historian. There seems to be evidence that some copper items were cast. From what I have read, the cast products would not generally qualify as 'art' and for that reason have understandably been ignored by art historians.

This from the guy who has just written that the task can be undertaken by low-skilled workers?

Neither. The claim merely is that some copper items have been cast.
Eric Stevens
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Eric Stevens wrote:

<snip>
Eric,          In the case of the copper artifacts in the upper Great Lakes area, all of the shapes and structures have been shown to have been made via cold and hot-working techniques. (Note that I am not saying that all the copper artifacts were so made; only that casting was not necessary.) As for whether certain types of tools and ornaments might be more easily made by casting, this is only true if the technology for casting has been developed. That is what is at issue.

    Yes, especially wrt copper (see Gary's discussion of copper casting problems below). So far as I can see at this point, there isn't good evidence for such a period of development in the archaeological record.
    OTOH, at least for the Old Copper and Red Ochre complexes in the Upper Great Lakes region, there don't seem to be many well-documented sites from that period (ca. 3000-1000 BC); and stratified sites are even more rare. Most of the copper artifacts were surface finds, and many came from collectors whose documentation of their finds generally ranged from fair to non-existent.

    Again, I don't know that that is true wrt copper, given the difficulty the technique appears to have in creating strong, high-quality results. OTOH, cold and hot working were known by the Native peoples in the Great Lakes ares to produce that very strong, high-quality result.
<snip>

    Eric, I read that to mean that casting, in general (as with iron, silver, bronze, gold, etc.) can be done by folks with fewer skills than smiths. However, copper appears to present particular problems with casting that are not so pronounced with other metals, and which require higher skill levels than would be required by those who cast other metals.
    This should be taken into consideration along with the fact that Great Lakes copper, and drift copper, don't need to be smelted to use. In other areas, where smelting ore _is_ required, the technology for melting metal is a given; here, it isn't.

    Eric, Yuri was making the claim that to say Indians of the Great Lakes area didn't cast copper was to express bigotry towards the First Nations of the area. Gary's argument flows from Yuri's standard 'mainstreamers are racists' rap, with its particular application in the cast vs. worked copper issue.
    I'm still agnostic, and am reading up on the archaeological references I can find. If you, or other folks, have suggestions for reading, I'm all eyes.
    BTW, I've just gotten Mallery's book (the 1979 version, revised and extended by Mary Roberts Harrison). I've only skimmed a bit of it, so I don't have an informed opinion on it yet. Will advise.
Tom McDonald
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On Wed, 23 Jun 2004 23:46:01 -0500, Tom McDonald

This is not my understanding. Metallurgical examination has shown that some of the artifacts have been cast.

That seems to be a different topic. Are you saying that even if they were found to be cast, it wasn't necessary for them to be cast?

I think you and I are approaching the question from opposite ends. You seem to be saying that no artifacts can have been cast, in the absence of direct evidence for casting techniques. I am saying that cast artifacts are evidence for the existence of casting techniques, even if direct evidence for such techniques is not known.

I don't read 'low skilled' as meaning 'lower skilled'.

There is a difference between 'smelted' as in refinining and 'melted' as for casting. I am not aware of evidence for the for the former in NA but there may be evidence for the latter in the form of cast artifacts.

Very much the curate's egg.
Eric Stevens
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Eric Stevens wrote:

Eric,
    That could be. That's why I wrote the below.
    My point here is that at least two researchers have done experiments using only cold and hot working, without casting, making all of the major types of artifacts found in the Great Lakes area. This is not to say that some might not have been cast. That's the issue. Contrary to what you write above, I have not yet completed my own look into whether some might have been cast. I'm not willing to take at face value reports of research the originals of which I haven't yet found.    

    It's the same topic. I was trying to avoid just this confusion by stating frankly that the research I mentioned does not rule out casting. And to your question, yes. I'm saying that it seems to me at this point that both casting and smithing could have produced the tools we find. The issue is whether both techniques were used, and if so over what time period and what places within the region.

    You mistake my meaning. I am saying that casting and smithing both could have been used. If there are artifacts that were cast, then that fact should inform future archaeological work.
    I'm not sure that you know this, but the main copper-using cultures of the upper Great Lakes areas are very poorly represented by habitation sites. In Wisconsin and the UP of Michigan, there are only a few such sites that have been found and studied from this period (Late Archaic to the transition to Early Woodland--ca. 3-4000 to ca. 100 BC).
    There are a great many sites with copper artifacts, but they are mostly either surface finds, or are in mortuary contexts; not where the ancient smiths/foundryfolk might have been expected to ply their trades
    I am less sanguine than you that old reports for which we have only second-hand sources, and for which we don't know the caveats and limitations of the researchers, can be accepted uncritically in the face of nearly unanimous statement from those who have studied the copper artifacts intensively that they haven't found convincing evidence of casting. However, I take offense at the suggestion that I've ruled out casting when I am actually looking into the issue with an open mind.

    Read it again. No mention of 'low skilled'. Merely that a smith needs 'higher level of skill' than a foundryman. A neurosurgeon may need a 'higher level of skill' than a dermatologist. Does this make the dermatologist 'low skilled'?q

    Of course smelting ore and melting for casting are different. However, if one needs and has the technology for smelting, melting for casting is not a technological leap. If one does not need to smelt ore, then melting it for casting requires that technological leap. The issue is whether that leap was made in this case. If cast artifacts are found, then looking for evidence of the development of that technology would be a higher archaeological priority than it is now.

    I'm not familiar with that. Will you explain for me?
Tom McDonald
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On Fri, 25 Jun 2004 19:24:15 -0500, Tom McDonald

Fair enough. You may remember that some years ago I reported that I had tried to track down Mallery's papers (left to the Smithsonian on his death) to obtain copies of the originals upon which he relied, but all the papers seem to have vanished into a black hole. It might be worth another try.

Only if your assessment is based on simplistic visual examination. Appropriate metallurgical tests are unambiguous.

I didn't say, or even imply, that you have unconditionally ruled out the possibility of cast artifacts.

Gary Coffman originally wrote of casting "It allows relatively low skilled workers to produce ... " and it was to this which I originally repsonded. My point was that casting is not a low skilled technique.

But is the fundamental proposition correct, that a dermatologist is necessarily of lower skill than a neurosurgeon? My observation is that while the disciplines are different, the skill levels are equally high in each.

The discovery of either smelting or melting would initially be accidental. I could think of circumstances in which melting could still occur when working with pure meteoric copper.

I do not share your certainty. Cast artifacts do seem to have been found. I am not aware that the reports cited by Mallery have been followed up in any way. As far as I can tell, nobody has even followed them up for the purpose of showing that they were wrong or that Mallery has misinterpreted them. The whole subject seems to have been treated as a non-issue.

A 19th century 'Punch' cartoon. The very new curate is having breakfast with his bishop and finds the boiled egg he has been served is rotten. The curate lacks the courage to complain about the bishop's breakfast fodder but the expression on his face alerts the bishop to the fact that all is not well. The bishop then asks ' ... and how is your egg?' The curate still too nervous to say the egg is rotten replies "Parts of it are excellent, my lord". That last is the comment I applied to Mallery's book.
Eric Stevens
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