Hello!
I have a platinum ring I need to resize. I need to enlarge it
approximately 1 to 2 US ring sizes. Looking at the shank, I don’t
want to thin it so I want to cut it and splice some metal into it.
The ring is marked PT900. I’ve been looking at Stuller and H&S for
rectangular stock and they do not carry any PT900, although I can
get it as a custom order.
Can I use PT950/Ru or PT950/Co stock to resize this ring? What kind
of problems could I encounter if I attempt to do this?
Thanks,
Ron
Torch or laser welder? The cobalt alloy is lightly magnetic. Test
both the ring and the piece with a magnet and see if either stick at
all, if not they should work. Torching platinum is harder. If you
know someone with a laser, take a six pack over and see if you can
use it.
hi Ron
No worries using a richer alloy. The richer allos have higher
melting point but will have colour close enough to match without
being obvious.
If you have never welded platinum before there are some things you
should know however. If you know this please disregard.
-
don’t use any flux. platinum and palladium do not like it if you
use flux. they will become contaminated and brittle.
-
use an oxidizing flame. adjust your torch so a small bright blue
cone is all you see, no outer soft blue cone no orange showing.
-
use a small focused torch tip and no need to heat up anything but
the area you are trying to weld. this means you can use a heat stop
on any stones on the head of the ring. if it is a ladies ring i use
a #3 tip on my smith little torch oxy act. very rarely do i need to
use anything larger but you will not need to go past a #4 even on a
mans heavier ring.
-
the metal will radiate light and look like it is going to melt
before the solder flows. don’t second guess it. keep going until the
solder flows. platinum has a very high melting point and welds very
nicely. the first time you do this it will freak you out and you
will think it is all going to hell in a hand basket but the solder
will flow long before the metal melts. the key is small focused
flame close but not touching the metal.
-
use protective welding glasses. the light radiation is bad for
your eyes.
-
do not pickle. you will not need to as you will not be using
flux. it will clean up and smith to the right shape very nicely. I
usually size up slightly smaller so that i can smith a bit to get
shape right without the need for filing and sanding to much.
platinum is a chore to finish so the less you need to do the better.
I love working in platinum an find it easier to work than gold. you
can work on very focused areas. Usually the thing that stops people
from working platinum is the cost of the material but if you have
worked silver and gold you will find platinum is much easier to deal
with. it will stay cleaner and weld easier. just keep an eye on it
and make sure you heat it enough to allow the solder to flow right
through the join
if you don’t get it the first time you just need to re heat it. no
new application of solder or flux is needed.
hope this helps
Les
Can I use PT950/Ru or PT950/Co stock to resize this ring? What
kind of problems could I encounter if I attempt to do this?
Yes. You can use the other alloys. There can be a very slight
difference in color, but you’d have to look very closely to see it,
and even then, maybe not.
If you do the sizing by using platinum solder to solder in a piece,
then the alternative alloys won’t matter so long as the solder is not
too high a melting point for the alloy you’re using. Some of the
alternative alloys melt slightly lower than iridium platinum (pt900
is most likely iridium/platinum). If you use solder, I strongly
recommend the “plumb” platinum solders rather than traditional types,
which have less platinum in them. The traditional types, unless you
use the highest melting grades, produce seams that can polish out, or
show a difference in color. The plumb solders are invisible after
soldering and cleaning up the joints.
If you use either a torch or laser to weld/fuse the seams, then any
difference in the melting points may require slightly more skill to
get a properly done seam without areas at corners/edges getting
melted in, forming depressions you then have to fill in. With a
laser, it’s a minor problem. torch fusing can be a little trickier.
But you can do it. Between Ru or Co alloys, I’d choose the Ru alloys
for this.
Peter
I always try to use the same alloy when sizing platinum or gold. The
different alloys have different melt temps.
I prefer to fuse rather than use solder when sizing. Still do it old
school with a natural gas torch. I keep the different alloys of plat
separated and labeled. Each alloy has it’s uses. We like 10%
Irridium for hand fabrication. I like ruthenium plat. for cast
pieces. Big commercial casters like cobalt plat for casting, but I’m
not a fan of it.
Have fun and make lots of jewelry.
Jo Haemer
timothywgreen.com
I know it has been a while since I asked this question, but I was able to get it soldered together with no problems (at least it hasn’t broken apart or disintegrated in the last two years) 
Thank you all for the words of wisdom!