Sizing a platinum ring

Hello everyone,

I came across a problem recently sizing a platinum ring and wondered
if anyone else has had this experience.

Stamped 950 Plat, looks and feels like platinum when you file it,

When heat was applied for the 1700 solder the ring started to
bubble. Upon further investigation, the inside of the ring looks like
a hershey crunch bar or a bad casting, all crazed and pitted. Put a
file to it, clean it up and it looks fine. The laser turned the metal
Grey in color so that was out. Had to seattle on 1500 solder which
did not make the metal bubble but yet there is not a faint dark line
where it was sized.

Is ther a new alloy that is now being used with platinum?

Any help for future problems of this sort would be of great help.

Thanks everyone,

First thing are you sure it is stamped plat and not 950PD, which
would be palladium.

Bill Wismar

not sure how experience you are so please forgive me if i state
things that you already know when working platinum you dont use flux
you use an oxidizing (oxi rich) flame if you try to use any other
alloy solder other than palladium or platinum you will contaminate
the metal and it will become brittle and sponge like if you need to
add material to make it bigger you must use platinum. Not seeing the
ring in question if it is platinum it sound like you are not the
first one to work on it and the person before did not follow these
rules. Or it was not cast in a proper set up not following these


Cobalt alloys give you this hassle. Stuller is one company using this
alloy in most all their castings. Several other design houses are
also going to this alloy. (Martin Flyer and Jeff Cooper are a couple)
If you use 1600 Stuller solder carefully, you can solder near
seamlessly. I believe that the cobalt alloy is a lot harder than
most others, casts with less problems but is a total pain to work
with from a bench jewelers point of view. Stuller’s website give a
lot of on how to work with it.

Tom Tilney

Any help for future problems of this sort would be of great help. 

Does it stick to a magnet?

If this is a cast piece then I would suspect that it is Pt/Co alloy.
It has a lower melting point than the Pt/Ru or Pt/Ir alloys. It also
oxidizes due to the base metal (cobalt) content. One way to know is
to check the item with a magnet, Pt/Co is slightly magnetic so if
you can get a little attraction to a magnet then it is platinum
cobalt alloy.

The main reason for using this alloy is that it casts so much better
than any of the other platinum alloys. It fills better with a finer
surface finish and has way less in the way of porosity issues. This
is why Stuller and the other major manufacturers use it in their cast
product. The down side is that it is softer than Pt/Ru.

James Binnion
James Binnion Metal Arts

Yes, I am experienced with all aspects of platinum but you made some
very valid points for those who are not. Yes, it is stamped 950
Plat., not 950 PD (have worked with that, what a pain). No, I have
not tested it for magnification.20

Thank you everyone for the info. I actually called Stuller and spoke
with someone who was really no help at all when it came to the
colbalt. Perhaps I will call again and ask for someone a bit more
knowledable for the next time I run across this situation.


I’ve worked with the cobalt platinum and find it a joy. (and it
sticks to a magnet which is why I asked that in an earlier post)

Could this platinum ring actually be palladium ? There is not much
difference in color, but the melting points are quite different.

Tom Arnold

I have also had this experience.In my situation the 950 platinum ring
was a cobalt alloy. This melts at a much lower temperature than
ruthenium/iridium alloys. It is also difficult to weld. I usually end
up using 1500 plat solder. There are two reliable tests. apply a
strong magnet to the ring, and if there is an attraction it is a
cobalt alloy. The other you described. When you heat the shank, it
will turn blue.

Hope this helps.