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5% cobalt/platinum

Hey, what do you all think of Stullers announcement that they
are now turning out castings with a new 5% cobalt 95% platinum
alloy? Seems that this metal can’t be welded with traditional
methods, oxidizes, is slightly magnetic and easily contaminated
with small particles of iron…have I remembered all the
problems? Oh, it shouldn’t be coated with boric acid because it
could become brittle after heating. Well, what do you think?

Bruce D. Holmgrain E-mail:
Snail Mail: POB 7972,McLean, VA 22106

I think one should not be afraid of Pt/CO 95/5 . In Europe it
has been the alloy of choice for platinum castings for many
years. The fact that ANY platinum alloy is easily contaminated is
well known and a clean work space will remedy that. The benefits
are clear. Pt/CO makes better castings as it flows better, the
finished product will hold its polish better as it is harder. The
slight oxidation during the soldering process is not a problem.
Just avoid solder containing Cadmium. Using 1700 welding solder
it is not a problem to size these rings. That extra step after
soldering to remove the slight oxidation will become routine, as
did fire coating for gold . If you have any technical questions
about platinum feel free to call the PGI hotline at (714) 760-8882

Jurgen J. Maerz, Mgr. technical education PLATINUM GUILD

Just in case there are some people out there who don’t receive
the Stuller newsletter, “Finding Facts”: here is a direct quote
from the January 1997 issue on the subject of platinum & cobalt.

"Stuller cast platinum products are made from a 95/5
Platinum-Cobalt alloy. Because this alloy behaves differently
than 90/10 Platinum-Iridium alloy, we wanted to give you the
following tips on using the metal. Since cobalt is
ferro-magnetic, like iron, this alloy is slightly magnetic. You
should avoid contamination of the piece with magnetized bench
scrap. The melting temperature of this alloy is 1765 degrees C
(3209 degrees F), compared to 1800 degrees C (3272 degrees F) for
90/10 Platinum-Iridium alloy. This difference makes fusing the
two alloys practically impossible.

"When sizing a shank made from this alloy, use a 1700 degrees C
solder. When joining this alloy to gold, use a cadmium-free
karat gold solder. Cadmium will migrate into the grain
boundaries of this alloy, causing brittleness.

“This alloy will tarnish (oxidize) during soldering. Do not
coat the piece with boric acid prior to soldering, as this will
lead to brittleness and breaking along the joint. After
soldering, coat with boric, heat to approximately 1200 degrees F
(low red color), and pickle to remove the oxides.”

I hope this makes the overall picture more clear. Happy

Joel Kahn <@Joel_Kahn>
Comptroller for Maxon’s Jewelers
Diamond Merchants & Estate Jewelers
Authorized Dealer for Rolex & Tag Heuer
2622 S Glenstone, Springfield Missouri 65804 USA
Voice: 417-887-1800 or 417-887-1809
Fax: 417-887-3422