On Tue, 15 Jun 2004 05:29:28 GMT, Seppo Renfors wrote:
Gary Coffman wrote:
On Thu, 10 Jun 2004 15:36:41 -0400, Yuri Kuchinsky wrote:
Copper Casting In America (Trevelyan)
[..]
So here we see the sort of an anti-Native bigotry that is
still all too common within our professional archaeological
establishment. These folks really still live in the middle
ages!

What a dark snake-pit of racism and bigotry our academic
establishment is... This never ceases to amaze me, I must
say.

This is the Dumbing-Down Crew that is hard at work to deny
the cultural achievements of Native Americans.

Realize that casting is primarily a technique used for cheap mass
produced items. It allows relatively low skilled workers to produce
large numbers of relatively complex identical items. Cold working is
a much more challenging, and artistically unique, way to produce
intricate copper ceremonial items. The smith has to have a higher
level of skill than the foundryman to produce equally complex work.

Given that, it seems to me that your claims of bigotry by a art
historian are unfounded. If anything, the idea that the art objects
were produced by cold work makes them even more impressive
examples of the skill of the worker than if they were mere castings.

Whilst there is little argument with that, it is still illogical to
believe that casting wasn't done. Each maker of jewellery, ceremonial
items would have ended up with "scraps" of copper. It is unlikely they
would have simply been thrown away. The annealing of copper would
bring it to melting temperature often enough for smaller thinner bits.
It suggests a very likely occurrence that they did melt copper, if for
no other reason than to make bigger pieces out of the small scraps and
off-cuts. This they would again cold work another time.

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.

Note too that the annealing temperature of copper is *way* below
the melting point. If they did melt parts of an object they were
annealing, they were using grossly too much heat. In other words,
it would be a mark of incompetence on their part if evidence of
such melting were found.

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.

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.

(Bronze is a different matter, of course, but there still has been
no evidence presented of bronze artifacts from the locale and
period under discussion in this thread.)

But that said, casting pure copper is a bitch. Porosity is the enemy,
even for modern copper founders. They charge a hefty premium for
low porosity castings. Alloying the copper to make bronze improves
matters *enormously*, and production of such alloys was a huge
technological leap forward for the casting industry.

*If* the Native Americans of millenia past made the technological
leap of producing bronze alloy, it would be a significant achievement
(as it was when Old World artisans did it). But I've seen no evidence
produced in this thread that the ancient Native Americans made
such a technological leap forward.

IIRC silver is found in with copper deposits in the Great Lakes area
and it has a melting point a bit lower lower than copper. It is likely
they could have used a silver/copper alloy or "bronze". If the
minerals co-exist then there is no need for "mixing", it is automatic
as with arsenic/copper deposits.

A quick search of the UNS database doesn't show any silver-copper
binary alloy listed as suitable for casting. Nor is such a binary mixture
called bronze.

The search did turn up "nickel silver" copper alloys suitable for casting,
but the composition of those alloys *contains no silver*. They do contain
large amounts of tin, nickel, and a bit of lead. All of the binary alloys of
silver and copper listed are labeled as "wrought", meaning that they
are suitable only for cold work.

The associated native copper and silver found in the Keweenaw
Peninsula is known as "Halfbreed". It isn't even an alloy (solid
solution). It consists of intertwined gross crystals of the two
separate metals. It is difficult to produce an alloy of silver and
copper in the absence of tin.

If you heat a sample of Halfbreed, the silver melts out before
the copper reaches melting temperature, leaving a mass of
copper with voids where the silver was. It does not produce
bronze.

The presence of tin is usually, though not always (aluminum
bronze being the primary exception), a prerequisite for a
copper alloy to be called bronze. I'm unaware of any tin
deposits in the UP of Michigan.

Note, an alloy of arsenic and copper was once called bronze
too, but it is dangerous to produce, and exceedingly brittle in
use. Old World artisans very quickly abandoned it. Again, no
evidence of artifacts from the UP of Michigan composed of
that alloy has been presented.

The artifacts described appear to all be relatively pure native copper.
As such, the *intelligent* way of working the material would have
been smithing rather than casting. So if the motive were to make
ancient Native Americans appear stupid, then claiming that they
used open casting techniques would be the method of choice to do
so. Now ask yourself which side of the argument is making that
claim.

You see, the thing is that cold working something doesn't require
"technology", where melting/smelting does. It is the implied lack of
technology where the suggested prejudices arise from.

Hmph! You might remember that one of the newsgroups where this
thread is appearing is the *metalworking* group. Most of the members
are machinists, either by vocation or avocation. In other words, their
primary occupation is working of metals at temperatures below the
melting point. They would *strongly* object to the notion that casting
should be the signature mark of metalworking technology.

Most of the more advanced technological working of metal is done
cold, or at least at temperatures below the melting point of the metal.
That's *particularly* true for pure copper. Most of the more astute
members would never even consider casting as a viable method for
producing pure copper objects.

Note that I am not insisting that no copper casting industry existed
in the UP of Michigan in pre-Columbian times. At least one radiograph
I've seen seems to indicate copper which had been melted in atmosphere
at some point. But what I am saying here is that atmospheric copper
casting is a particularly unintelligent way of utilizing the pure metal
when the alternative of lower temperature smithing is available.

So the apparent fact that most of the artifacts found show evidence
that they were smithed rather than cast clearly indicates that the
Native Americans were sophisticated in the working of the copper
available to them. Insisting that they cast the objects instead would
be an attempt to show that the workers were *not* sophisticated.

A very important indicator of technological sophistication is knowing
how to choose the appropriate method to work with a particular
material. In this case, the technologically appropriate method is
*not* casting. So if your objective is to minimize the technical
prowess of the Native Americans, you'd be in the camp pushing
for copper casting. Casting dumb, smithing smart.

(Again I must point out that bronze is a different matter, but no
evidence has been presented to support the production of bronze
in the locale and time under discussion.)

Gary