On Sat, 18 Apr 2009 22:26:59 -0700, in rec.crafts.jewelry Muso
wrote:

I filled a one-tablespoon stainless
steel measuring spoon about half way full with zinc nuggets, and then
I heated the spoon with a propane torch. The torch made a red spot on
the side of the spoon, though the zinc did not seem to be melting.

Mike, it occurs to me to wonder if you're doing any research reading prior to
your experiments? If you had, you might have recognized that zinc, like lead,
like aluminum, or a number of other metals more reactive than gold or silver,
for oxide "dross" films quickly when melting. Even though the metal in the
spoon quickly melted, what you saw on the outside was a mess of zinc oxide. It
doesn't melt, so it completely hides what may be happening underneath to the
non-oxidized metal.

To some degree, this is unavoidable, since the grains/nuggets will already have
this on the surface, and when they melt, that rises to the top. Before pouring,
you'll want to brush off that mess so you're only pouring molten metal, not lots
of mixed in oxide crud too.

Another fix is to use a melting flux. Ordinary soft soldering acid flux, such
as plumbers use would do the trick just fine, And if you use a softer flame,
and actually hold the flame over the metal, the reducing atmospher of the flame
itself (the part of the flame past the inner blue cone, but still within the
glowing part of the flame, not way past where it's just very hot gases), that
part of the flame has little oxygen, so the metal stays cleaner during melting.

By the way, using clean zinc grain to begin with, unlike what you get from
murdering pennies, would drastically reduce the amount of oxide crud you have to
deal with... (grin)

Peter