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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#41
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Copper Casting In America (Trevelyan)
On Sun, 27 Jun 2004 02:58:26 -0400, Gary Coffman
wrote: On Fri, 18 Jun 2004 16:34:00 GMT, Seppo Renfors wrote: Gary Coffman wrote: If they did open atmospheric casting (and I'd strongly contend they didn't have the technology to do any other kind, nobody did until the latter half of the 19th century, and then only as a laboratory curiosity), the resulting copper wouldn't be suitable for cold work, too much porosity. 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. It would be a problem, a big problem. If they did attempt to salvage copper scraps, they likely *hammer welded* them. That's done at temperatures below the melting point of copper, so porosity doesn't become as serious a problem. ....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. 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. You need to understand that copper behaves *differently* from silver, gold, or even iron. Those metals respond well to casting techniques. Nearly pure copper does not. 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. 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. 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. For a people without inert gas shielded continuous casting furnaces, it would be nothing but frustration. Don't under rate the cunning of anceint man. Eric Stevens |
#42
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Copper Casting In America (Trevelyan)
On Sun, 27 Jun 2004 03:11:14 -0400, Gary Coffman
wrote: On Sat, 26 Jun 2004 11:13:49 +1200, Eric Stevens wrote: On Wed, 23 Jun 2004 23:46:01 -0500, Tom McDonald wrote: 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. This is not my understanding. Metallurgical examination has shown that some of the artifacts have been cast. The evidence brought out in this thread is that *one* copper artifact shows radiographic evidence (characteristic porosity) for part of it being heated above the melting point in atmosphere at some point. That is in no way conclusive evidence of casting technology. The piece may have been an attempt at casting, or it may simply have been overheated while being worked. Maybe you missed it but http://www.iwaynet.com/~wdc/copper.htm was cited a few weeks ago in sci.archaeology and introduces evidence for the casting of copper. Arlington Mallery's book gives more details including the results of competent metallurgical examination. Eric Stevens |
#43
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Copper Casting In America (Trevelyan)
On Sun, 27 Jun 2004 03:03:50 -0400, Gary Coffman
wrote: On Wed, 23 Jun 2004 23:46:01 -0500, Tom McDonald wrote: Eric Stevens wrote: On Fri, 11 Jun 2004 22:57:04 GMT, (Gary Coffman) wrote: But that said, casting pure copper is a bitch. This from the guy who has just written that the task can be undertaken by low-skilled workers? 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. Exactly, and further, skill alone isn't sufficient to make sound castings of pure copper. The proper equipment is also required. Specifically, an inert atmosphere furnace. That technology didn't exist until the late 19th century. Just as well the ancient egyptians didn't know that they couldn't do what they were doing. :-) Eric Stevens |
#44
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Copper Casting In America (Trevelyan)
On Mon, 28 Jun 2004 09:04:49 +1200, Eric Stevens wrote:
On Sun, 27 Jun 2004 03:03:50 -0400, Gary Coffman wrote: On Wed, 23 Jun 2004 23:46:01 -0500, Tom McDonald wrote: Eric Stevens wrote: On Fri, 11 Jun 2004 22:57:04 GMT, (Gary Coffman) wrote: But that said, casting pure copper is a bitch. This from the guy who has just written that the task can be undertaken by low-skilled workers? 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. Exactly, and further, skill alone isn't sufficient to make sound castings of pure copper. The proper equipment is also required. Specifically, an inert atmosphere furnace. That technology didn't exist until the late 19th century. Just as well the ancient egyptians didn't know that they couldn't do what they were doing. :-) 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 |
#45
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Copper Casting In America (Trevelyan)
On Mon, 28 Jun 2004 09:04:48 +1200, Eric Stevens wrote:
On Sun, 27 Jun 2004 03:11:14 -0400, Gary Coffman wrote: On Sat, 26 Jun 2004 11:13:49 +1200, Eric Stevens wrote: On Wed, 23 Jun 2004 23:46:01 -0500, Tom McDonald wrote: 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. This is not my understanding. Metallurgical examination has shown that some of the artifacts have been cast. The evidence brought out in this thread is that *one* copper artifact shows radiographic evidence (characteristic porosity) for part of it being heated above the melting point in atmosphere at some point. That is in no way conclusive evidence of casting technology. The piece may have been an attempt at casting, or it may simply have been overheated while being worked. Maybe you missed it but http://www.iwaynet.com/~wdc/copper.htm was cited a few weeks ago in sci.archaeology and introduces evidence for the casting of copper. Arlington Mallery's book gives more details including the results of competent metallurgical examination. 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 |
#46
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Copper Casting In America (Trevelyan)
On Sun, 27 Jun 2004 14:59:04 -0500, Tom McDonald wrote:
Gary Coffman wrote: On Sun, 27 Jun 2004 13:18:58 -0500, Tom McDonald wrote: Gary Coffman wrote: The evidence brought out in this thread is that *one* copper artifact shows radiographic evidence (characteristic porosity) for part of it being heated above the melting point in atmosphere at some point. That is in no way conclusive evidence of casting technology. The piece may have been an attempt at casting, or it may simply have been overheated while being worked. Are you referring to the sort of amorphous, three-cornered blob listed in Conner's web site as 'R666', and in the Milwaukee Public Museum (where it's curated) as '55786': http://www.iwaynet.net/~wdc/copper.htm If so, I have found additional information about that piece. Yes, that's the one. What have you learned? I corresponded with Dr. Alex Barker of the Milwaukee Public Museum about this artifact, since they are curating it there. His response about the description of the artifact was as follows: "As to why one might wonder if it had been cast, it's relatively dense for its size, and one surface is fairly smooth and rounded--not like the upper surface of cast metal, however, but one might perhaps imagine it as the bottom of an irregular puddle of metal." 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. The description he gave seems to fit the photo on Connor's site. It doesn't look like any purpose-made artifact; but it does look as one might expect a bit of accidentally melted copper to look, if it just fell into the ashes of the fire and cooled there. To my untutored eye, at least. 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 |
#47
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Copper Casting In America (Trevelyan)
Gary Coffman wrote:
On Sun, 27 Jun 2004 14:59:04 -0500, Tom McDonald wrote: Gary Coffman wrote: On Sun, 27 Jun 2004 13:18:58 -0500, Tom McDonald wrote: Gary Coffman wrote: The evidence brought out in this thread is that *one* copper artifact shows radiographic evidence (characteristic porosity) for part of it being heated above the melting point in atmosphere at some point. That is in no way conclusive evidence of casting technology. The piece may have been an attempt at casting, or it may simply have been overheated while being worked. Are you referring to the sort of amorphous, three-cornered blob listed in Conner's web site as 'R666', and in the Milwaukee Public Museum (where it's curated) as '55786': http://www.iwaynet.net/~wdc/copper.htm If so, I have found additional information about that piece. Yes, that's the one. What have you learned? I corresponded with Dr. Alex Barker of the Milwaukee Public Museum about this artifact, since they are curating it there. His response about the description of the artifact was as follows: "As to why one might wonder if it had been cast, it's relatively dense for its size, and one surface is fairly smooth and rounded--not like the upper surface of cast metal, however, but one might perhaps imagine it as the bottom of an irregular puddle of metal." 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. 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. The description he gave seems to fit the photo on Connor's site. It doesn't look like any purpose-made artifact; but it does look as one might expect a bit of accidentally melted copper to look, if it just fell into the ashes of the fire and cooled there. To my untutored eye, at least. 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. 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. 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. 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. 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. 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 |
#48
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Copper Casting In America (Trevelyan)
On Sun, 27 Jun 2004 19:18:20 -0400, Gary Coffman
wrote: On Mon, 28 Jun 2004 09:04:48 +1200, Eric Stevens wrote: On Sun, 27 Jun 2004 03:11:14 -0400, Gary Coffman wrote: On Sat, 26 Jun 2004 11:13:49 +1200, Eric Stevens wrote: On Wed, 23 Jun 2004 23:46:01 -0500, Tom McDonald wrote: 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. This is not my understanding. Metallurgical examination has shown that some of the artifacts have been cast. The evidence brought out in this thread is that *one* copper artifact shows radiographic evidence (characteristic porosity) for part of it being heated above the melting point in atmosphere at some point. That is in no way conclusive evidence of casting technology. The piece may have been an attempt at casting, or it may simply have been overheated while being worked. Maybe you missed it but http://www.iwaynet.com/~wdc/copper.htm was cited a few weeks ago in sci.archaeology and introduces evidence for the casting of copper. Arlington Mallery's book gives more details including the results of competent metallurgical examination. 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. Did you see my Message-ID: in which I quote metallurgical aspects from Mallery? Eric Stevens |
#49
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Copper Casting In America (Trevelyan)
On Sun, 27 Jun 2004 19:00:11 -0400, Gary Coffman
wrote: On Mon, 28 Jun 2004 09:04:49 +1200, Eric Stevens wrote: On Sun, 27 Jun 2004 03:03:50 -0400, Gary Coffman wrote: On Wed, 23 Jun 2004 23:46:01 -0500, Tom McDonald wrote: Eric Stevens wrote: On Fri, 11 Jun 2004 22:57:04 GMT, (Gary Coffman) wrote: But that said, casting pure copper is a bitch. This from the guy who has just written that the task can be undertaken by low-skilled workers? 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. Exactly, and further, skill alone isn't sufficient to make sound castings of pure copper. The proper equipment is also required. Specifically, an inert atmosphere furnace. That technology didn't exist until the late 19th century. Just as well the ancient egyptians didn't know that they couldn't do what they were doing. :-) So, are you claiming to have evidence that the ancient Egyptians successfully cast pure native copper? Apart from the fact that it all depends what you mean by 'pure', yes, I have read to that effect. 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. While not directly addressing the point, you may be interested in http://www.lehigh.edu/~inarcmet/papers/jfa022002.pdf Eric Stevens |
#50
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Copper Casting In America (Trevelyan)
"Tom McDonald" skrev i meddelandet ... Gary Coffman wrote: On Sun, 27 Jun 2004 14:59:04 -0500, Tom McDonald wrote: Gary Coffman wrote: On Sun, 27 Jun 2004 13:18:58 -0500, Tom McDonald wrote: Gary Coffman wrote: The evidence brought out in this thread is that *one* copper artifact shows radiographic evidence (characteristic porosity) for part of it being heated above the melting point in atmosphere at some point. That is in no way conclusive evidence of casting technology. The piece may have been an attempt at casting, or it may simply have been overheated while being worked. Are you referring to the sort of amorphous, three-cornered blob listed in Conner's web site as 'R666', and in the Milwaukee Public Museum (where it's curated) as '55786': http://www.iwaynet.net/~wdc/copper.htm If so, I have found additional information about that piece. Yes, that's the one. What have you learned? I corresponded with Dr. Alex Barker of the Milwaukee Public Museum about this artifact, since they are curating it there. His response about the description of the artifact was as follows: "As to why one might wonder if it had been cast, it's relatively dense for its size, and one surface is fairly smooth and rounded--not like the upper surface of cast metal, however, but one might perhaps imagine it as the bottom of an irregular puddle of metal." 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. 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. The description he gave seems to fit the photo on Connor's site. It doesn't look like any purpose-made artifact; but it does look as one might expect a bit of accidentally melted copper to look, if it just fell into the ashes of the fire and cooled there. To my untutored eye, at least. 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. 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. 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. 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. 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 |
#51
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Copper Casting In America (Trevelyan)
On Mon, 28 Jun 2004 08:52:10 +1200, Eric Stevens wrote:
On Sun, 27 Jun 2004 02:58:26 -0400, Gary Coffman wrote: 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. But the question is, how pure was the copper. 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. 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. 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. For a people without inert gas shielded continuous casting furnaces, it would be nothing but frustration. Don't under rate the cunning of anceint man. 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 |
#52
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Copper Casting In America (Trevelyan)
On Mon, 28 Jun 2004 06:46:49 GMT, "Inger E Johansson" wrote:
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. 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 |
#53
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Copper Casting In America (Trevelyan)
On Mon, 28 Jun 2004 17:38:04 +1200, Eric Stevens wrote:
On Sun, 27 Jun 2004 19:00:11 -0400, Gary Coffman wrote: On Mon, 28 Jun 2004 09:04:49 +1200, Eric Stevens wrote: On Sun, 27 Jun 2004 03:03:50 -0400, Gary Coffman wrote: On Wed, 23 Jun 2004 23:46:01 -0500, Tom McDonald wrote: Eric Stevens wrote: On Fri, 11 Jun 2004 22:57:04 GMT, (Gary Coffman) wrote: But that said, casting pure copper is a bitch. This from the guy who has just written that the task can be undertaken by low-skilled workers? 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. Exactly, and further, skill alone isn't sufficient to make sound castings of pure copper. The proper equipment is also required. Specifically, an inert atmosphere furnace. That technology didn't exist until the late 19th century. Just as well the ancient egyptians didn't know that they couldn't do what they were doing. :-) So, are you claiming to have evidence that the ancient Egyptians successfully cast pure native copper? Apart from the fact that it all depends what you mean by 'pure', yes, I have read to that effect. 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. While not directly addressing the point, you may be interested in http://www.lehigh.edu/~inarcmet/papers/jfa022002.pdf 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 |
#54
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Copper Casting In America (Trevelyan)
Inger E Johansson wrote:
"Tom McDonald" skrev i meddelandet ... snip 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. 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 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 |
#55
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Copper Casting In America (Trevelyan)
Gary Coffman wrote:
On Mon, 28 Jun 2004 09:04:49 +1200, Eric Stevens wrote: On Sun, 27 Jun 2004 03:03:50 -0400, Gary Coffman wrote: On Wed, 23 Jun 2004 23:46:01 -0500, Tom McDonald wrote: Eric Stevens wrote: On Fri, 11 Jun 2004 22:57:04 GMT, (Gary Coffman) wrote: But that said, casting pure copper is a bitch. This from the guy who has just written that the task can be undertaken by low-skilled workers? 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. Exactly, and further, skill alone isn't sufficient to make sound castings of pure copper. The proper equipment is also required. Specifically, an inert atmosphere furnace. That technology didn't exist until the late 19th century. Just as well the ancient egyptians didn't know that they couldn't do what they were doing. :-) 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 Well, Gary, the folowing sure seems to imply that the ancient Egyptian did some copper casting. [quote] Ancient Egyptian raw materials: metals - copper, bronze, iron, gold, silver, lead http://nefertiti.iwebland.com/trades/metals.htm 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. [unquote] Yuri. Yuri Kuchinsky -=O=- http://www.trends.ca/~yuku Reality is that which, when you stop believing in it, doesn't go away -=O=- Philip K. Dick |
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ancient copper casting outside N Am ( Copper Casting In America(Trevelyan)
Gary Coffman wrote:
On Wed, 23 Jun 2004 23:46:01 -0500, Tom McDonald wrote: Eric Stevens wrote: On Fri, 11 Jun 2004 22:57:04 GMT, (Gary Coffman) wrote: But that said, casting pure copper is a bitch. This from the guy who has just written that the task can be undertaken by low-skilled workers? 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. Exactly, and further, skill alone isn't sufficient to make sound castings of pure copper. The proper equipment is also required. Specifically, an inert atmosphere furnace. That technology didn't exist until the late 19th century. Gary 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. [quotes] INDIA http://www.hindunet.org/hindu_histor.../artefacts.htm Melting of native copper was done by putting the regulus [lump of copper] over furnace or fire in a crucible and then casting it. IRELAND Copper and Tin Mining in Ireland in the Bronze Age http://www.thecelticplanet.com/mining.htm It is estimated that in the early Bronze Age in Ireland, not more than 14% of artifacts were of bronze. The remainder were made from copper only SOUTHERN SIBERIA http://faculty.web.waseda.ac.jp/yukis/sougen13.mei.html Intriguingly, the majority of cauldrons recovered in southern Siberia were also made of pure copper instead of tin bronze. According to Bogdanova-Berezobskaya (1963: 136, 153), among the twenty cauldrons analyzed, thirteen are pure copper, five arsenical copper (As 1-1.5%), one tin bronze, and one Cu-Sn-Pb alloy. [the date range above seems to be 7th-8th centuries BC] http://www.thecopperlink.com/product...i-of_index.php the oldest artefacts are not made of copper tin alloys, they are made of pure copper. Some examples of early smelted copper artefacts: -- 3800 BC Spatula, Chisel, Awl - Iran (Yahya) -- 3500 BC Flat axe - Egypt [end quotes] So it's never too late to educate yourself about such things, Gary. Best regards, Yuri. Yuri Kuchinsky -=O=- http://www.trends.ca/~yuku Reality is that which, when you stop believing in it, doesn't go away -=O=- Philip K. Dick |
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Copper Casting In America (Trevelyan)
Yuri Kuchinsky wrote:
Gary Coffman wrote: On Mon, 28 Jun 2004 09:04:49 +1200, Eric Stevens wrote: On Sun, 27 Jun 2004 03:03:50 -0400, Gary Coffman wrote: On Wed, 23 Jun 2004 23:46:01 -0500, Tom McDonald wrote: Eric Stevens wrote: On Fri, 11 Jun 2004 22:57:04 GMT, (Gary Coffman) wrote: But that said, casting pure copper is a bitch. This from the guy who has just written that the task can be undertaken by low-skilled workers? 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. Exactly, and further, skill alone isn't sufficient to make sound castings of pure copper. The proper equipment is also required. Specifically, an inert atmosphere furnace. That technology didn't exist until the late 19th century. Just as well the ancient egyptians didn't know that they couldn't do what they were doing. :-) 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 Well, Gary, the folowing sure seems to imply that the ancient Egyptian did some copper casting. [quote] Ancient Egyptian raw materials: metals - copper, bronze, iron, gold, silver, lead http://nefertiti.iwebland.com/trades/metals.htm 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. [unquote] 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 |
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Copper Casting In America (Trevelyan)
On Mon, 28 Jun 2004 13:22:35 -0400, Gary Coffman
wrote: On Mon, 28 Jun 2004 17:38:04 +1200, Eric Stevens wrote: On Sun, 27 Jun 2004 19:00:11 -0400, Gary Coffman wrote: On Mon, 28 Jun 2004 09:04:49 +1200, Eric Stevens wrote: On Sun, 27 Jun 2004 03:03:50 -0400, Gary Coffman wrote: On Wed, 23 Jun 2004 23:46:01 -0500, Tom McDonald wrote: Eric Stevens wrote: On Fri, 11 Jun 2004 22:57:04 GMT, (Gary Coffman) wrote: But that said, casting pure copper is a bitch. This from the guy who has just written that the task can be undertaken by low-skilled workers? 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. Exactly, and further, skill alone isn't sufficient to make sound castings of pure copper. The proper equipment is also required. Specifically, an inert atmosphere furnace. That technology didn't exist until the late 19th century. Just as well the ancient egyptians didn't know that they couldn't do what they were doing. :-) So, are you claiming to have evidence that the ancient Egyptians successfully cast pure native copper? Apart from the fact that it all depends what you mean by 'pure', yes, I have read to that effect. 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. While not directly addressing the point, you may be interested in http://www.lehigh.edu/~inarcmet/papers/jfa022002.pdf 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. As I said, it all depends upon what you mean by 'pure'. Eric Stevens |
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Copper Casting In America (Trevelyan)
On Mon, 28 Jun 2004 13:07:35 -0400, Gary Coffman
wrote: On Mon, 28 Jun 2004 08:52:10 +1200, Eric Stevens wrote: On Sun, 27 Jun 2004 02:58:26 -0400, Gary Coffman wrote: 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. But the question is, how pure was the copper. 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. 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. 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. 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 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. A good bed of well ventilated charcoal will suffice. One often finds melted copper in the remains of burned out buildings. For a people without inert gas shielded continuous casting furnaces, it would be nothing but frustration. Don't under rate the cunning of anceint man. 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. 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. 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. Only if they used the relatively pure meteoric copper of Michigan. It was laikely to be naturally alloyed if it was smelted. 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. But it wasn't the only source of copper. Eric Stevens |
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Copper Casting In America (Trevelyan)
Eric Stevens wrote:
On Mon, 28 Jun 2004 13:07:35 -0400, Gary Coffman wrote: snip 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. But it wasn't the only source of copper. 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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Copper Casting In America (Trevelyan)
Tom McDonald wrote in message ... 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 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. ..http://www.geo.msu.edu/geo333/gold.html 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 |
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Copper Casting In America (Trevelyan)
On Tue, 29 Jun 2004 09:49:39 +1200, Eric Stevens wrote:
On Mon, 28 Jun 2004 13:07:35 -0400, Gary Coffman wrote: On Mon, 28 Jun 2004 08:52:10 +1200, Eric Stevens wrote: On Sun, 27 Jun 2004 02:58:26 -0400, Gary Coffman wrote: 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. But the question is, how pure was the copper. 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. 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. 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. 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. 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 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. A good bed of well ventilated charcoal will suffice. One often finds melted copper in the remains of burned out buildings. 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. 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. Only if they used the relatively pure meteoric copper of Michigan. It was laikely to be naturally alloyed if it was smelted. 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. 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. But it wasn't the only source of 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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Copper Casting In America (Trevelyan)
Paul K. Dickman wrote:
Tom McDonald wrote in message ... 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 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. .http://www.geo.msu.edu/geo333/gold.html 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 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 |
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Copper Casting In America (Trevelyan)
On Mon, 28 Jun 2004 21:45:11 -0400, Gary Coffman
wrote: On Tue, 29 Jun 2004 09:49:39 +1200, Eric Stevens wrote: On Mon, 28 Jun 2004 13:07:35 -0400, Gary Coffman wrote: On Mon, 28 Jun 2004 08:52:10 +1200, Eric Stevens wrote: On Sun, 27 Jun 2004 02:58:26 -0400, Gary Coffman wrote: 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. But the question is, how pure was the copper. 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. 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. 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. 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. The quote is a procedure for smelting chalcopyrite ore. I don't know where you get that from. The opening sentence says very clearly "In fire-refining copper ... ". That's a very different procedure from what is required to process pure native copper. Apples and oranges. 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. 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. A good bed of well ventilated charcoal will suffice. One often finds melted copper in the remains of burned out buildings. 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. 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. 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. That's a very different question from the use of coal to prevent oxidisation. 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. Only if they used the relatively pure meteoric copper of Michigan. It was laikely to be naturally alloyed if it was smelted. Meteoric copper? Perhaps you're thinking of iron. 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/collecto...r/vft/mi2c.htm 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. Only in some places. 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. But it wasn't the only source of 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 Eric Stevens |
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Gary Coffman wrote: On Mon, 28 Jun 2004 08:52:10 +1200, Eric Stevens wrote: On Sun, 27 Jun 2004 02:58:26 -0400, Gary Coffman wrote: 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. But the question is, how pure was the copper. 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. 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. 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. For a people without inert gas shielded continuous casting furnaces, it would be nothing but frustration. Don't under rate the cunning of anceint man. 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. See: http://www.iwaynet.net/~wdc/copper.htm The 4th and 5th pictures down. 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. 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. -- SIR - Philosopher unauthorised ----------------------------------------------------------------- The one who is educated from the wrong books is not educated, he is misled. ----------------------------------------------------------------- |
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Tom McDonald wrote: Gary Coffman wrote: [..] 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. 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. 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!! http://www.iwaynet.net/~wdc/copper.htm As it is, it looks as though I'll have to dig for other examples that might show casting. 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. -- SIR - Philosopher unauthorised ----------------------------------------------------------------- The one who is educated from the wrong books is not educated, he is misled. ----------------------------------------------------------------- |
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Tom McDonald wrote: Eric Stevens wrote: On Mon, 28 Jun 2004 13:22:35 -0400, Gary Coffman wrote: On Mon, 28 Jun 2004 17:38:04 +1200, Eric Stevens wrote: [..] While not directly addressing the point, you may be interested in http://www.lehigh.edu/~inarcmet/papers/jfa022002.pdf 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. As I said, it all depends upon what you mean by 'pure'. 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. http://www.dayooper.com/Networks.JPG The copper may well be 99% pure - what about the rest? It isn't every day people find huge lumps of pure copper without impurities embedded within it. This is the dilemma that people bypass and ignore. This has a good story about the Great lakes Copper deposits. http://www.geo.msu.edu/geo333/copper.html [..] -- SIR - Philosopher unauthorised ----------------------------------------------------------------- The one who is educated from the wrong books is not educated, he is misled. ----------------------------------------------------------------- |
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On Tue, 29 Jun 2004 05:48:01 GMT, Seppo Renfors wrote:
Gary Coffman wrote: 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. See: http://www.iwaynet.net/~wdc/copper.htm The 4th and 5th pictures down. 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. 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. 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. 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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Seppo Renfors wrote:
Tom McDonald wrote: Gary Coffman wrote: [..] 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. 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. 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!! http://www.iwaynet.net/~wdc/copper.htm 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. As it is, it looks as though I'll have to dig for other examples that might show casting. 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. 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 |
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Seppo Renfors wrote:
Tom McDonald wrote: Eric Stevens wrote: On Mon, 28 Jun 2004 13:22:35 -0400, Gary Coffman wrote: On Mon, 28 Jun 2004 17:38:04 +1200, Eric Stevens wrote: [..] While not directly addressing the point, you may be interested in http://www.lehigh.edu/~inarcmet/papers/jfa022002.pdf 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. As I said, it all depends upon what you mean by 'pure'. 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. http://www.dayooper.com/Networks.JPG The copper may well be 99% pure - what about the rest? It isn't every day people find huge lumps of pure copper without impurities embedded within it. This is the dilemma that people bypass and ignore. This has a good story about the Great lakes Copper deposits. http://www.geo.msu.edu/geo333/copper.html [..] 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 |
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Tom McDonald wrote in message ... 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 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 |
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Paul K. Dickman wrote:
Tom McDonald wrote in message ... 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 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. http://www.csasi.org/2003_summer_jou..._poundings.htm http://www.csasi.org/2003_spring_jou..._poundings.htm http://www.csasi.org/2004_january_jo...er_process.htm In the 1947 book, _Indians Before Columbus_, by Paul S. Martin, George I. Quimby and Donald Collier, all in the Anthropology Department of the Chicago Natural History Museum, I found this on page 42: "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 |
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On Mon, 28 Jun 2004 21:31:53 -0500, Tom McDonald wrote:
Paul K. Dickman wrote: 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. .http://www.geo.msu.edu/geo333/gold.html 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 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. 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 |
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Copper Casting In America (Trevelyan)
On Tue, 29 Jun 2004 07:05:25 GMT, Seppo Renfors wrote:
Tom McDonald wrote: 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. http://www.dayooper.com/Networks.JPG The copper may well be 99% pure - what about the rest? It isn't every day people find huge lumps of pure copper without impurities embedded within it. This is the dilemma that people bypass and ignore. This has a good story about the Great lakes Copper deposits. http://www.geo.msu.edu/geo333/copper.html 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 |
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Copper Casting In America (Trevelyan)
Apparently on date Wed, 30 Jun 2004 04:08:35 -0400, Gary Coffman
said: 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). 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. |
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Copper Casting In America (Trevelyan)
Martyn Harrison wrote:
Apparently on date Wed, 30 Jun 2004 04:08:35 -0400, Gary Coffman said: 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). 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 |
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Copper Casting In America (Trevelyan)
Gary Coffman wrote:
[snip] The apparent fact that the Native Americans *didn't* cast native copper This is a "fact" only if you disregard all evidence to the contrary, as you appear to be doing. 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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Copper Casting In America (Trevelyan)
Gary Coffman wrote:
On Tue, 29 Jun 2004 05:48:01 GMT, Seppo Renfors wrote: 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. 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, 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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Copper Casting In America (Trevelyan)
Tom McDonald wrote:
Yuri Kuchinsky wrote: Gary Coffman wrote: On Mon, 28 Jun 2004 09:04:49 +1200, Eric Stevens wrote: On Sun, 27 Jun 2004 03:03:50 -0400, Gary Coffman wrote: On Wed, 23 Jun 2004 23:46:01 -0500, Tom McDonald wrote: Eric Stevens wrote: On Fri, 11 Jun 2004 22:57:04 GMT, (Gary Coffman) wrote: But that said, casting pure copper is a bitch. This from the guy who has just written that the task can be undertaken by low-skilled workers? 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. Exactly, and further, skill alone isn't sufficient to make sound castings of pure copper. The proper equipment is also required. Specifically, an inert atmosphere furnace. That technology didn't exist until the late 19th century. Just as well the ancient egyptians didn't know that they couldn't do what they were doing. :-) 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 Well, Gary, the folowing sure seems to imply that the ancient Egyptian did some copper casting. [quote] Ancient Egyptian raw materials: metals - copper, bronze, iron, gold, silver, lead http://nefertiti.iwebland.com/trades/metals.htm 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. [unquote] 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 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=- 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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