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