Copper Casting In America (Trevelyan)

Maybe you missed it but

Eric Stevens

Just as well the ancient egyptians didn't know that they couldn't do what they were doing. :-)

Eric Stevens

So, are you claiming to have evidence that the ancient Egyptians successfully cast pure native copper?

The metallurgical references I have say that native copper was extremely rare in Egypt. Almost all of the copper they had was refined from ores (smelted), and the results were *not* pure copper. Rather, they were alloys, whether intentional or not, of copper, arsenic, zinc, iron, or tin. These alloys behave *very* differently from pure native copper when casting is attempted.

Gary

No, I didn't miss it. That's where the reference to artifact R666 was found. None of the other artifacts shown present convincing evidence (characteristic porosity) of having been poured in atmosphere.

Gary

Interesting that he'd characterize it as "relatively dense for its size". The density measurement reported on the web site says it is less dense than ordinary native copper (8.2 vs 8.9). That's consistent with the porosity shown in the radiograph.

I suspect that Dr Barker has neither metallurgical nor geological training. So his density report is just that of a layman picking up a hunk of metal. But if I'm wrong in that supposition, then he is contradicting the information provided on the web site.

That would be significant in itself. The heat required to melt such a mass of copper can't be produced in an ordinary open wood fire. A forced draft fire burning a high carbon fuel such as charcoal or actual metallurgical grade coal would normally be required to supply the heat necessary to melt that mass.

Now that's consistent with a smith's forge or a casting furnace. It isn't consistent with an ordinary wood fire used to anneal worked native copper. So that lends support to the thesis that the ancient Native Americans controlled such a high temperature technology.

OTOH, a forest fire can produce sufficient natural draft to reach the required temperature. So it is *possible* that R666 was in such a natural fire. That would explain what we see in the radiograph without the necessity of claiming high temperature technology for the ancient Native Americans.

The fact that we have only one artifact showing the characteristic porosity we'd expect from native copper melted in atmosphere lends credence to the latter hypothesis. If we saw a *lot* of artifacts from different locations showing characteristic porosity, that'd be another story. But no good evidence has been presented to support that, certainly not the other examples on the web site. The radiographs of other items on the site are more consistent with wrought items than cast items.

As I mentioned previously, surface blisters are not what we're looking for in terms of the porosity characteristic of pure copper casting. What we need to see is a foam of microscopic bubbles, and clusters of tiny visible bubbles deep in the metal on the radiographs. That's absent from the other radiographs on the site.

Gary

Gary,

He has a background in anthropology, so I wouldn't expect that he would necessarily have much in the way of metallurgical training, and his geology might be limited. As you noted, his observation on the heaviness of the object seemed to belie amateur status in those fields.

I'm not arguing about the details reported in Conner's web site. I'm just concerned that his and his sources may have gone beyond the evidence in certain cases.

I'm getting around to reading two detailed archaeological reports on the Riverside site, as well as a short report on mortuary issues at the site written by Lewis Binford. You have helped me frame some key questions to keep in mind when reading them. In addition to the obvious (copper artifacts and cremation details), you've got me looking for localized, atypical hearths and discussions about charcoal and/or ash that might be from forest fires instead of controlled hearth or cremation fires. Thanks.

What strikes me about the copper blob we're discussing is that if it were to have been overpour or other waste from a casting event, I'd expect it to have been added to a 'try again' pile, to be melted with other smaller bits for later casting. Of course, it could have just been forgotten. I'll have to look in the reports for indications of ceramics, with a specific concern for what might have been used as crucibles.

Yes, that's why I was interested in your take on R666/55786. If there were other good examples of melted copper, I'd have expected that the web site would have presented them. As it is, it looks as though I'll have to dig for other examples that might show casting.

Tom McDonald

Did you see my Message-ID: in which I quote metallurgical aspects from Mallery?

Eric Stevens

Apart from the fact that it all depends what you mean by 'pure', yes, I have read to that effect.

While not directly addressing the point, you may be interested in

Eric Stevens

If I remember it correctly, saw a report at my friend's house the other day, it was in an Ohio site such was found or at least ceramics found was believed to have been used as crucibles.

Inger E

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

What I've seen since I started looking into this is a report of a purported ceramic mold fragment discovered in Ohio. However, there is considerable disagreement as to whether that actually is a mold fragment or not. It is also far from the native copper sites being discussed, and hasn't been dated to the time frame under discussion. So it sheds very little light on the subject of pure copper casting.

Gary

While not Egyptian, and the artifacts analyzed show evidence of being wrought rather than cast, the chemical analysis does back my position. The metals being worked were alloys, not pure native copper.

Gary

Inger,

I'd like to have information about that site in Ohio. I'm especially interested in:

Date(s) and culture(s) of the ceramics;

Reports and photos about the potential crucibles;

Location(s) of the find(s);

References to work on the artifacts, and/or primary investigator(s) on the studies.

Thanks.

Tom McDonald

Well, Gary, the folowing sure seems to imply that the ancient Egyptian did some copper casting.

Ancient Egyptian raw materials: metals - copper, bronze, iron, gold, silver, lead

Re: copper objects [rather than bronze]:

The objects were generally cast, which is quite difficult to do with copper because of the formation of gas bubbles during the pouring of the metal and its shrinking when it cooled down. Then they were hammered cold to give them their final form.

Yuri.

Yuri Kuchinsky -=O=-

Hi, Gary,

Here you seem to be implying that copper casting wasn't done in the ancient world at all.

You couldn't be more wrong, my friend... Sure seems to me like you're not very knowledgeable about the ways that the ancient peoples worked with metals.

And this implies that your general knowledge about metalworking is rather deficient, since you've reached the above conclusion based on it, rather than on your familiarity with archaeological evidence.

So here's some archaeological evidence for a change, that refutes your speculations about the ancient peoples not casting pure copper.

INDIA

IRELAND

Copper and Tin Mining in Ireland in the Bronze Age

SOUTHERN SIBERIA

Some examples of early smelted copper artefacts:

-- 3800 BC Spatula, Chisel, Awl - Iran (Yahya)

-- 3500 BC Flat axe - Egypt

So it's never too late to educate yourself about such things, Gary.

Best regards,

Yuri.

Yuri Kuchinsky -=O=-

Yuri,

Your site tells us that copper ore was what was available, not native copper; and that it had to be smelted before use. IOW, it's not clear whether the Egyptians ever had copper of the purity of the native copper in the upper Great Lakes area. In addition, the smelting and melting of that copper would more than likely have resulted in a copper alloy, not pure copper.

Of course, if you have better evidence that shows Egyptians cast 99+% pure copper, you are welcome to present it here. I for one would be very interested in that evidence.

Tom McDonald

As I said, it all depends upon what you mean by 'pure'.

Eric Stevens

On Mon, 28 Jun 2004 13:07:35 -0400, Gary Coffman 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

Eric,

In the context of this thread, at least its original context, the copper was native copper in the upper Great Lakes area of the US and Canada. That copper is typically well over 99% pure out of the ground, and does not have to be smelted to remove impurities. If another context is in evidence, then a definition of the term 'pure' is needed.

In the cases Yuri noted (e.g.: Egypt, Harrapa, China), that copper was apparently smelted from ore, and analysis of individual artifacts would be necessary to describe the ratio of copper to alloy materials. In one of Yuri's examples, 'pure' copper artifacts were all below 98.8% copper.

I agree, therefore, that one cannot take a statement that some artifact or artifact type was 'pure copper' at face value. It needs to be quantified.

Tom McDonald