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. For a people
without inert gas shielded continuous casting furnaces, it would be
nothing but frustration.

Gary