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[How2] Identify Platinum alloys


How can those of us that do trade work on all these Platinum
alloys Identify them & tell them apart!

Mark Chapman


How can those of us that do trade work on all these Platinum
alloys Identify them & tell them apart!

It’s tricky… mostly 'cause it’s still a new problem to most
of us.

But. Most platinum articles should be marked. If marked 900,
then assume iridium platinum, most likely. I’d assume iridio
platinum as well, on U.S. made goods that are unmarked or marked
just platinum when it comes from smaller shops and craftpeople,
or is handmade, or otherwise might be from a shop less likely to
have a more difficult to use “900 plat” stamp available. Much
of the older stuff is simply marked “plat” or “pt” with no
numerical indication, but is nevertheless 10% iridium. (New FTC
regs say that 900 platinum must be marked as such, not just
plat.) And many individual craftpeople or smaller manufacturers
may take some time to bother getting the newer stamps.

The odd or more difficult to use alloys are going to almost
always be castings, not fabricated pieces. At least in the U.S.
Almost all handmade work is most likely to be iridio platinum.

Marked 950, it’s most likely a ruthenium platinum, in the U.S.,
unless it comes from a manufacturer known to use Cobalt.

You can tell the cobalt platinum alloys because they are
slightly magnetic. You should have a GOOD strong magnet around
the shop anyway, to remove steel/iron filings and saw blades etc.
from your scrap, especially from the platinum scrap.

With the new alloys from Kretchmer/Hoover and Strong, you’ll
have to hope you’re forwarned, unless the alloy is marked
differently than you’d expect.

Note that with ruthenium platinum, intermixing it, such as in a
ring sizing, with iridio platinum, is not likely to cause you any
problems. Try not to mix the two types if you are recycling bits
and pieces. reuse (as in, melting to make new ingots for rolling
etc.) only pieces who’s identity you know for certain.

Hope this helps.

Peter Rowe


Dear Mark, Good question. Aside from the occasional ( and I do
mean occasional !)quality stamp that identifies the constituent
alloy, I know only of using a magnet against filings or a
graver-removed sliver for the presence of magnetic attraction to
detect the cobalt alloy. Jurgen Maerz’s entry, I think,
described some color differences that might help. As I’ve
stated before, “When in doubt, Weld with pure platinum”.

I recall about a year ago or so, Platina Casting (a division of
Alex Primak in N.Y.) wanted to introduce “14K platinum”,i.e. 585
parts pure platinum to some other metal or metals. They also
wanted to introduce, likewise, a “18K plat” alloy as well.
Thankfully, it hasn’t been well received at all! Can you imagine
having to identify such alloys as well as stocking all the
appropriate solders? What a potential nightmare! I, for one,
hope we never see such stuff.


Mark, If it is Platinum Cobalt, it is magnetic. If it is
anything else it is not. Just remember to weld the shank when you
size. If you have problems, stop, re examine the shank for
oxidation, and if present, solder with 1700. Call me if you have
more problems Jurgen 949 760-8279


Re: determining whether an allow is magnetic or not.

Actually this is easy, suspend a very small very strong magnet
from a silk thread as a pendulum slightly above the bench, and
mark the center position. Bring the suspect alloy, ring whatever
into contact with the magnet and see if you can pull the magnet
off center with it, if you can the allow is magnetic, if not it
is not.