Copper Casting In America (Trevelyan)

wrote:


going
to
develop
this
other
copper yes, bronze yes, silver yes(to pour in forms) but not iron. That they didn't do until they began trading silver, furs and eagles with the Norse according to the oral tradition I have had from respected Indians I spoken to.
Inger E
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Gary Coffman wrote:

I agree that is most likely to have been the procedure. On the other hand what we don't really know is if the porosity was a problem for them.

I suspect you are using modern ideas as a guide, knowing of other techniques etc. Back then in learning about melting copper, they must observe it melt. Learning annealing they again need to observe the effects, thereby also learning to heat to just below melting point and lend itself to the "hammer welding" you refer to below.

....and it would also eliminate porosity, would it not? So the small bit could well be melted and cast into a small ingot - to later "hammer weld" the porosity out of it.

I'm aware of the difficulty - as well as the evidence it provides of casting. As such evidence does exist, even if not widely, it indicates the ability to melt copper.

Try the old 3 cent piece - it was silver + copper alloy. Nor does it need to be "fit for casting" in the modern sense, as all I see it used for is to generate a larger lump of material to work with as a smith would.

A copper alloy is in general called "bronze" irrespective of the mix (eg arsenic + copper) except when it is called "brass" (nickle + copper?).

No, it has been done a lot of the time. In Sweden (damn I lost the info tag..) they have something they call "malm" (ore) that is a bronze, but a far redder colour than normal bronze. I can't tell you the mix of it as I lost the info. However there is a lot of arsenic + copper bronze around in Asia Minor. It was mined in the Ural mountains as a ready mixed ore.

It does if you heat it to the melting point of copper.
http://ia.essortment.com/threecentcoin_rlzk.htm

Tin is indeed the most common, but not the sole mix.

It is still called "bronze" as the "bronze age" term itself says.

Ahhh.... but irrespective of the fact that artisans may get their nose out of joint, melting/smelting metals IS called a "technology". So having that technology under ones belt in addition to the smithing, is indeed one up on the smithing alone :-)

Not suggesting modern people do cast copper - I am saying ancient people did.

While there is/was almost pure copper available at the time, much of it had impurities embedded within it. Large hunks of pure copper were relatively rare. The vast amounts that are indicated to have been mined must include copper with much impurities or copper embedded in other material. This had to be refined somehow, melting is the simplest way of refining it - unless you know of another technique available to the ancients.

Nobody is suggesting that smithing isn't an extremely skilled occupation..... but then so is flint knapping in my view. The casting was not used to manufacture anything much apparently. I see it as a refining process to later be hammered at near melting temperatures, thereby producing fine artefacts.

As I said mastering one technology, is less than mastering TWO technologies.... if you want to call smithing a "technology" in favour of Art :-)

I don't know what if any testing of composition of artefacts has been done. Some bronzes only contain 3 -> 5% tin elsewhere. If none are done then a claim that bronze doesn't exist can't be made. Testing the metals would also finger print them for origin, which hasn't been done either to my knowledge.
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Seppo Renfors wrote:

<monster snip>
Considering copper :
1. find some rich ore or native or near native. 2. build one hot fire - continue burning and increase coal / charcoal contents. 3. add copper or ore - perhaps using glass technology of the time - pit glass ? more melted stone that is glassy and use this slab as a cookie sheet . :-) 4. cover the top with more fuel and then cap it off - perhaps air vent on the side of the wind...
A reduction fire - and when cooled off it might have metal in the sheet...
Maybe.
Martin
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@ home at Lion's Lair with our computer snipped-for-privacy@pacbell.net
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It would be a problem, a big problem.

No, it couldn't. Porosity isn't just little bubbles in the metal. Those bubbles contain air, and at molten temperatures, the oxygen in that air would oxidize the inside of the bubble. So what you wind up with is a mass of copper with a lot of oxidized holes in it. You can't weld copper that is oxidized. If this happens when a modern TIG welder is welding copper (gas shield failure), the only thing he can do is grind out all the porosity and start over.

No trick to melting copper. Doing something intelligent with the molten metal in an atmospheric environment is a different matter. As I noted previously, casting pure copper is difficult, even today. For a people without inert gas shielded continuous casting furnaces, it would be nothing but frustration.
Gary
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wrote:

But the question is, how pure was the copper.
In any case, copper can mostly by prevented from oxidising by melting it under a layer of crushed coal or charcoal. In fact this method was used for the production of largely deoxised (tough-pitch) copper in recent time.

Don't under rate the cunning of anceint man.
Eric Stevens
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The native copper we've been discussing is very high purity. The halfbreed ore does contain silver, but the silver isn't in solid solution with the copper (copper-silver alloys are difficult to produce). Instead it is in the form of distinct crystal inclusions which would melt out and separate before the copper would melt.

A graphite cover was used to prevent oxidation while melting (coal won't work because of the large fraction of volatiles, charcoal might be useable). But you also have to deal with the air entrained when pouring.
A bottom pour furnace is helpful, but you really need deoxidizers in the alloy to prevent severe porosity problems. Tin and zinc are the preferred deoxidizers. Arsenic also works, but the fumes are deadly. Lead makes the metal more fluid, and assists in filling out the mold. None of those are naturally present in the native copper we're discussing.
Also, as a side note, where is the evidence for coal mining or large scale charcoal production in the area? You don't get to copper melting temperatures with a simple wood fire. You need a forced draft fire with a high carbon fuel.

Don't underestimate the difficulty of getting sound pure copper castings. Low alloy bronzes and brasses (approx 0.5% to 1% tin or zinc respectively) aren't too bad to cast, high alloy bronzes and brasses are easy. But casting pure copper is hard, even with today's technology.
Again, porosity is the problem, and that should show up on radiographs, as it does for R666 (which certainly shows evidence of being melted in atmosphere, though not necessarily evidence of being cast), but none of the other artifacts presented show that sort of porosity.
I believe we are agreed that only atmospheric casting was within reach of the ancient Native Americans (or ancient Old World founders for that matter), so we *should* see characteristic porosity in any pure copper items they attempted to cast. Now of course the Old Worlders had the advantage of ores which did contain suitable deoxidizers. They weren't actually casting pure copper. But the Michigan copper was essentially pure native copper.
Gary
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wrote:

Here is a quote from 'Metallurgy for Engineers' Rollason, 2nd Edition, first published 1939:
Begin quote: --------------------------------- Production of Tough Pitch Copper. In fire-refining copper the impurities are removed by oxidising the metal until about 4 per cent copper oxide (Cu20) is absorbed. During this stage the impurities form oxides more readily than the copper and are removed as a slag or evolved as gas. The last impurity so removed is sulphur which is not completely driven off as sulphur dioxide by mere oxidation, but to remove the last traces the metal has to be violently agitated by poling, i.e. introducing an unseasoned piece of wood under the surface. This causes a miniature fountain of molten copper, and allows the air to come into contact with the spraying metal. Small test castings or button castings are taken to indicate the state of the metal. With sulphur present the ingot spurts just as it goes solid due to the evolution of gas (SO2), but as the sulphur is reduced in amount the surface of the ingot sinks in the manner normal to most metals. If a micro-examination is made of this metal it will be found to contain globules of copper oxide in the form of a eutectic (Cu-Cu2O). A layer of crushed coal is then placed on the molten copper, and as poling continues the copper oxide is reduced and when a content of about 0.04 to 0.08 per cent oxygen is reached the surface of the button remains level and the properties of the metal are good, in other words "tough." The lower the oxygen, the higher the so-called "pitch" and vice versa, hence the name "Tough Pitch." As poling continues past this point the copper absorbs hydrogen from the furnace gases and when cast the metal rises on solidification. These changes in behaviour, micro-structure and mechanical properties are due to the influence of hydrogen and oxygen on the copper. ---------------------------------------- End quote
The above confirms not only the use of crushed coal but also the primitive nature of the processes by means of which relatively pure copper was produced even in the 20th century. Stirring with a piece of unseasoned wood is a practice which may have roots going back for millenia.
My point is that our ancestors have had a habit of producing materials with primitive techniques which we have now largely forgotten about. The fact the we now do things only with modern gizmos doen't mean that our ancestors couldn't do much the same thing some other way.

A good bed of well ventilated charcoal will suffice. One often finds melted copper in the remains of burned out buildings.

Once again, it depends what you mean by pure. Somewhere I have seen reference to a recognised ancient copper alloy containing 0.5% As which was produced by addition of the As. Clearly they were able to produce copper with less than that level of As.

Only if they used the relatively pure meteoric copper of Michigan. It was laikely to be naturally alloyed if it was smelted.

But it wasn't the only source of copper.
Eric Stevens
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Eric Stevens wrote:

<snip>
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
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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
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wrote:

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 http://www.minsocam.org/MSA/collectors_corner/vft/mi2c.htm

Only in some places.

Eric Stevens
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Gary Coffman wrote:

See: http://www.iwaynet.net/~wdc/copper.htm
The 4th and 5th pictures down.

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.
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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
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Gary Coffman wrote:

Not everything that is possible is probable.
Wishing won't make it so.
Yuri.
Yuri Kuchinsky -=O=- http://www.trends.ca/~yuku
A great many people think they are thinking when they are merely rearranging their prejudices -=O=- William James
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Yuri Kuchinsky wrote:

Yuri,
    Exactly. So why are you clinging to your wishful thinking, instead of researching the issue?
Tom McDonald
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Gary Coffman wrote:

[..]
They disagree with you as it states "The casting bubble can clearly been seen...."

In my experience of examples of all kinds - no two are ever identical.

Again, I point to the fact they disagree.

One cant make that claim without investigation, there hasn't been any undertaking by others do examine artefacts for casting. Again I point to the article:
Neiburger said "Further xeroradiographic surveys and analysis of the 25,000 existing copper artifacts from that period (Archic Midwestern United States) are necessary for the determination of how extensively early Native Americans had used melted metal."
It doesn't look like any real studies has been done to say casting was NOT practised - or that it was. Personally I don't expect a hell of a lot of casting due to the pure copper being available (even if not always in large lumps) - but I cannot dismiss the evidence, limited as it is, considering the LACK of research undertaken so far.

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Seppo Renfors wrote:

    Gary showed that the porosity typical of pure cast copper is not present in that artifact. He even explained in just below.

    Do you know what 'characteristic' means in this application?

    It appears 'they' were mistaken.

    Yes, there has. Please note that every artifact that does not show the internal characteristics of melted copper is evidence against that item being cast. And, as Gary and Paul have pointed out, when an artifact shows clear evidence of having been made by smithing, that is evidence against it having been cast.
Again I point

    I fully agree, and hope that more such studies are done.

    We've been looking at the evidence for a bit now, on this thread. The evidence for casting that's been presented so far appears to have suffered in the course of examination. That said, I would very much like to see more investigation done on this subject.

    Seppo, would you care to comment on this last by Gary?
Tom McDonald
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Tom McDonald wrote:

Please point out the "porosity" in this sample:
Two copper pigs:
http://people.uncw.edu/simmonss/P6030052.JPG
The casting is obvious in this:
http://people.uncw.edu/simmonss/LA_1240-1.4.jpg
Both pictures show melted copper - pre Colombian melted copper! It leaves Gary's statements hanging in the air.
However if one considers that "bubbling" has been claimed to be caused by "overheating" in a annealing process - then it is saying "melted" at the same time, as it cannot bubble UNLESS a portion of it is melted. Also "welding" requires the melting of the metal - or so goddamned close to it that the friction heat generated by a blow on it does melt the metal.
Those are two logical examples of melting occurring - the knowledge of melting copper existed. It beggars belief that scraps and off cuts were NOT melted when the process must have been known to them. That people suggest they would rather go and do hard manual labour another day to find a piece "just right" for the job, when it is right there, right now, right before them. All they have to do is melt it into one lump.
The implied suggestion they would rather do the hard labour, and not proceed with the easier option available immediately to them, isn't consistent with known human behaviour.
[..]
SIR - Philosopher unauthorised ----------------------------------------------------------------- The one who is educated from the wrong books is not educated, he is misled. -----------------------------------------------------------------
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Seppo Renfors wrote:

Seppo,
    First, the porosity would be most likely visible on radiographs, or in a section through the bubbles. You haven't given me the information necessary to determine this for these copper pieces.
    Second, no one argues that no copper was ever melted in pre-Columbian North America. The question, especially for the upper Great Lakes area, is whether this was done by humans; and if so, whether it was done on purpose to make tools or ornaments.
    Third, the artifacts shown are from Lamanai, Belize, and date from after about 1200 AD. They have el zippo to do with copper work in the Upper Great Lakes area in the Archaic. Is that why you posted links to the photos, but not to the web page they're on? That page specifies all this:
"Copper and bronze (copper-tin and copper-arsenic) began to arrive at Lamanai during the 13th century AD. Provenience studies conducted by Dr. Dorothy Hosler at the Massachusetts Institute of Technology revealed that the copper used to produce many of these items was obtained from West Mexican ore fields."
http://people.uncw.edu/simmonss/lamanai.htm

    This is grasping at straws, Seppo.

    Woulda coulda shoulda. As Inger what value to place on 'what-if's'.

    The implied suggestion is that the Indians wisely used the techniques that produced the best tools and ornaments for them.
    As Gary has pointed out, often, and you seem not to have grasped, casting pure copper is very inferior to forging pure copper in terms of the quality of the finished product. Choosing to use a process that produces a lower quality result over a well-known process that produces a higher quality result is not consistent with known human behavior.
Tom McDonald

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Tom McDonald wrote:

Indeed. The fact of "bubbles" doesn't necessarily point to of "overheating" while annealing. That radiographs are needed to determine casting means it cannot be determined from a visual inspection unless a un-worked piece eg like the small pigs in the picture. This work hasn't been done for the artefacts that I can find - therefor I cannot give it - nor can you then claim "not cast" for them.

You certainly could have fooled me. I has seen a number of instances where it is claimed no s/melting was needed the copper was worked by hammering. That embeds the statement "no s/melting".

I highly recommend you withdraw that and rephrase it - lest you want to be seen saying "native people are not humans"!!

The web site URL is posted in another message. The pictures were the relevant part for this issue of "obvious porosity". Again you are wanting to look at the label, ignoring the content!

I just take the opportunity to remind you that West Mexico is in "North America".

What "straws"? Is the above right or wrong? Where is your common sense? Note the picture again where I point to casting is obvious - that picture suggests a considerable overheating of the metal to have that result. This simple fact points to problems with temperature control - it would be no different when annealing something - temperature can (and is so claimed) get too high so the material melts. Them not noting this is suggesting people are (A) blind (B) stupid. I say they were aware of the method required to melt copper. Why do you disagree considering your earlier statement "no one argues that no copper was ever melted" - but yet you do exactly that right here.

None of the above applies at all Tom - you are operating with a closed mind at present, and doing your damnedest to contradict your claim "no one argues that no copper was ever melted"!!

You would further argue that they elect doing something that is much harder in favour of something that is easier. This is unrealistic. It is a very modern notion to make bikes that go absolutely nowhere, even when pedalled for hours!

I suggest you look at Paul's message, and follow the links therein:

Again, as it almost always is, there is more to this than meets the eye - the simple claim "casting makes poorer quality - therefor it wasn't done" is far, far too simplistic.
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wrote:

Reasonably pure copper can be welded at ambient temperatures merely by pressure. MIllions of electrical connections rely on this property.

Eric Stevens
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