What's with this new platinum?

I had to finish, size and set a platinum ring alloyed with cobalt.
I really don't like the color or the way it works.
And the damned crap is magnetic fer Pete's sake!
Who thinks these things up? Stuller?
Jeez!

On Sat, 05 May 2007 20:14:19 -0700, in rec.crafts.jewelry Frosty
wrote:

I had to finish, size and set a platinum ring alloyed with cobalt.
I really don't like the color or the way it works.
And the damned crap is magnetic fer Pete's sake!
Who thinks these things up? Stuller?
Jeez!

It's not all that new, Ray. Cobalt / platinum has been around for at least 15
years or so. It was developed, along with a number of other platinum alloys, in
response to the increased demand for cast platinum products. Standard iridium
platinum is great for fabrication and hand working, but is rather problematic to
cast, being more prone to porosity and shrinkage problems than casters would
like. Cobalt platinum melts a little easier, and over a slightly wider
temperature range (difference between liquidus and solidus), and, with modern
casting equipment (by which I mean modern induction melt, controlled atmosphere
motor driven centrifuge machines), gives substantially higher quality castings
with fewer rejects due to shrinkage cavities or porosity in the finished
castings. It's often slightly harder, making it a little easier to polish too.
And cobalt is cheaper than iridium too.

When working it, you're right that at the bench, it's less nice to work with,
largely because it oxidizes. But that pickles off again. Not quite as ductile
as iridio platinum either, but in properly annealed, should be easy enough to
set. It's magnetic propeties are an advantage, for the most part, making it
easy to identify, and not getting in the way of normal working. It does mean
you keep the stuff that sticks to a magnet now, since in addition to iron, which
you want to remove from your mixed filings, it also removes the cobalt platinum.
But that's not bad, since now you can remove most of the cobalt platinum from
mixed gold and platinum scrap, making for better refining yields (that is, if
you only work with cobalt platinum.). Iron can be cleaned from those filings
with a quick wash in acid if you like.

It IS important to know when you're working a cobalt alloy, since if you need to
weld it, it doesn't torch weld as well as iridio platinum, and certainly not if
you're accidentally using iridio platinum as welding filler (like filler wire in
a laser welder, for example). But the "plumb" platinum solders from PMWest work
very well with it, perhaps better than welding, and leave no trace of a visible
seam if done well. If using traditional platinum solders, you'll likely want
to avoid the highest melting grades, due to cobalt platinum's lower melting
point.

As I said, the stuff is intended for casting, nothing much else. In that role,
it's an improvement from some standpoints (largly from the caster's perspective,
but also from the view of whomever would otherwise have to deal with surface
porosity.) For those of us on the bench, it's not much of an improvement at
all, and for some, an annoyance, since you can't treat it like iridium platinum.
but it's OK when you get used to the slightly different rules.

Peter

Frosty wrote:
I had to finish, size and set a platinum ring alloyed with cobalt.
I really don't like the color or the way it works.
And the damned crap is magnetic fer Pete's sake!
Who thinks these things up? Stuller?
Jeez!

Ah Stuller!, ... the Mircrosoft of the jewelry industry.

--
Abrasha
http://www.abrasha.com

On Sun, 06 May 2007 16:05:09 GMT in rec.crafts.jewelry Abrasha
, intended to write something intelligible, but
instead wrote :

Frosty wrote:
I had to finish, size and set a platinum ring alloyed with cobalt.
I really don't like the color or the way it works.
And the damned crap is magnetic fer Pete's sake!
Who thinks these things up? Stuller?
Jeez!

Ah Stuller!, ... the Mircrosoft of the jewelry industry.

LOL!!!! SO true!