On Mon, 05 Jul 2004 01:49:44 GMT, Seppo Renfors wrote:
"Paul K. Dickman" wrote:
Seppo Renfors wrote:
Are you suggesting the "tears" are the result of (A) the pure copper having
been melted (B) because it is pure copper?

They are a result of the small air bubbles trapped throughout the metal
caused by melting it in less than controlled conditions.

I can understand that during a melting process where molecules are at
their most active, some reaction to air and a certain amount of mixing
can occur.

Atmospheric oxygen actually dissolves in molten copper, much as CO2
is dissolved in a soft drink. Take a common Coke, put it in the freezer,
come back in 30 minutes and pop the top. You get a foamy mess. The
same thing happens when molten copper freezes. The oxygen tries to
common back out of solution, causing the foamy mess copper workers
call characteristic porosity.

What I find difficult is that an annealing process causes
bubbles -UNLESS it is overheated to a melting point locally. How else
does something get INTO the metal to cause bubbles when it is pure to
begin with?

How about when the native copper was formed? Masses of native
copper typically have small inclusions, bits of rock, silver, etc. In
particular, in the Keewenaw range, calcium carbonate inclusions
are common (refer back to the frequently referenced article giving
the geology of the region).

When calcium carbonate is heated, it decomposes into CO2 and
calcium oxide fume. The CO2 will blow a blister if the inclusion is
near the surface of the piece of heated native copper being
annealed.

You have to understand that native copper is chemically pure
(99+%) metallic copper by definition, but it is deposited in a rock
matrix where it is later found and mined. Small inclusions are
common. They aren't *chemically* combined with the copper,
the copper is still pure, but they are *mechanically* combined
with it.

Gary