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