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