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   Report Post  
Old June 27th 04, 10:52 PM
Eric Stevens
 
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Default 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   Report Post  
Old June 27th 04, 11:04 PM
Eric Stevens
 
Posts: n/a
Default 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

  #44   Report Post  
Old June 28th 04, 01:00 AM
Gary Coffman
 
Posts: n/a
Default 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   Report Post  
Old June 28th 04, 01:18 AM
Gary Coffman
 
Posts: n/a
Default 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   Report Post  
Old June 28th 04, 02:45 AM
Gary Coffman
 
Posts: n/a
Default 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   Report Post  
Old June 28th 04, 04:40 AM
Tom McDonald
 
Posts: n/a
Default 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   Report Post  
Old June 28th 04, 07:38 AM
Eric Stevens
 
Posts: n/a
Default 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   Report Post  
Old June 28th 04, 07:38 AM
Eric Stevens
 
Posts: n/a
Default 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   Report Post  
Old June 28th 04, 08:46 AM
Inger E Johansson
 
Posts: n/a
Default 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





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