I have been welding platinum for years and for the most part
everything goes smoothly. Occasionally though, I come across rings
that feel and cut like platinum, will take the heat past red, & then
will simply melt at the joint. This same material will not
accommodate 1700 solders either. I have read that Plat AU has a
lower melting point and is becoming popular with the manufacturers
for its casting properties but I don’t think this is what I am
running into because it is relatively new.
Here’s the question: Is there a way of testing platinum before hand
to get a better feel for what the ring is actually made of and judge
how to approach it before lighting the torch? Platinum shanks get
expensive…obviously.
Also, when these problems occur how do others of you handle the job
for a clean finished outcome?
This happens to be a pet peeve of mine, I get trouble calls
regularly from jewelers who have no way of knowing what they are
working on. In my opinion, for this reason PT (only) stamping is a
HUGE disservice to the trade, just to cater to marketers who while
wringing their hands, claim the public just can not see the value in
90Pt/10Ir platinum jewelry compared to PT stamped jewelry. They will
never convince me. In my opinion any perceived advantage is offset by
bench jewelers mishandling the pieces while performing some ordinary
service like sizing.
At least with gold we can see if it is white or yellow, and act
accordingly! Too many “hidden” alloys will ruin the serviceability!
In your case a few things come to mind- You may be running into
palladium jewelry, or you may be running into heat treatable PT,
which often contains gallium and other low flow metals, resulting in
a flow point of around 1600 C. Jurgen Maerz once suggested to me that
the best way to ID heat treated PT is to take a very sharp graver and
engrave a bit off in an inconspicuous place. If the metal feels soft
and curls up it is regular PT. If it chips away in small bits it is
something else like HT platinum.
The number of PT alloys is growing. The downside of this 950PT
stamped PT with no hint of other metals is screwing up a bench
jeweler’s ability to correctly service thousands of pieces of very
finely made PT jewelry.
Hi Mark, There are several new platinum alloys that have been
formulated for casting that have lower melting temps Like Plat S
that melts at around 1600 C so your 1700C solder is much too hot.
The safe thing would be to stick to 1500C or lower melting platinum
solders or to use a laser. I don’t know of any way to tell the
difference between the various platinums short of an assay.
There are other alloys of platinum that are more likely the culprit.
Most likely you are running into pt/cobalt alloys. Some companies
have totally switched to pt/cobalt; Stuller is an example. Another
difficulty is palladium, though this is pretty rare. My
recommendation is to change from welding to the plumb platinum
solders put out by Precious Metals West or Hoover and Strong (I like
pmwest’s product a little better myself, but they are both good)
The easy solders are great on the pt/cobalt alloys (and lower
melting temp 900 pt alloys) and even the medium solders work OK, but
if you don’t have a lot of experience with using the plumb solders
you may have more problems in regards to melting so take a little
more care. The hard solders are great for the other platinum group
alloys that have higher melting temps like 950pt/iridium,
950pt/ruthenium and 999pt.
One trick with the plumb pt solders is to not use a solder pick in
the traditional manner. Instead, place a little spittle on the seam
with a clean pick then, with some saliva still on the pick touch the
pallion of solder and place it on the seam. Heat the seam very
slowly until the saliva has evaporated and then solder as usual.
The plumb solders just don’t work well with a solder pick.
Filing and sawing, or other techniques that require a sense of how
the different alloys feel are helpful ways of determining the type
of alloy, but they require a lot of practice and discrimination, but
this will probably work most of the time: First heat the shank to a
high red heat and let it air cool (protect any diamonds with boric
acid, don’t get it on the area where you are going to solder). If
it is pt/cobalt it will oxidize, if it is palladium it will oxidize
too so you still need to take some care, though palladium has a much
lower temp and is likely to melt. The other, nonoxidizing alloys
are a little more difficult to determine so If I wasn’t sure I would
use the easy plumb platinum solder and not risk it. After your
soldering is done, recoat the entire piece with boric acid and heat
to a very light red. After cooling, pickle the item and the
oxidation will be removed.
The S+ alloys from Hoover are also tricky to determine if they are
not stamped S+, but you can detect them by the way they file; they
are not as “sticky” as other platinum alloys and in fact feel much
more like gold alloys except in it’s heft. S+ alloys also have a
lower melting temperature and require the use of the easy pt solders
and the refluxing/pickling steps. These alloys may also have been
heat treated so care must be taken to note if the item seems to have
softened significantly after heating. Heat treating is a whole
other subject that I won’t go into, but be aware that it can be a
factor.
I’ve not worked with the newest pt/au alloy, but it sounds fun.
The bottom line is that the use of platinum is prolific and has
never been more rewarding or difficult to work with. Those who
choose to learn the ins and outs of this metal, can really demand
good pay; there’s always someone out there who will butcher it so
specialists will be more and more in demand.
This is surely Jurgen’s territory, but I’ve had quite a bit of
experience with platinum so I’ll contribute. For sizing platinum
rings, I’ve completely abandoned the old platinum solders in favor of
the newer platinum plumb solders, which melt at 1350, 1450, and 1550
Celsius (I believe those are the temperatures). This would be low
enough for the new HT platinum’s alloys, but you’d probably be wise
to use the lowest temperature solder, live with the slight gray line,
and get in and out quickly since you’ll still be somewhat close to
the melting temperature of the parent metal. You can identify the
platinum cobalt allows, which are favored for delicate castings since
they have a lower melting temperature and finish easier, because they
are slightly magnetic. Lay the article on the table and touch a
strong magnet to it and it will stick slightly, and it the article
is light, will partially pick it up off the table. If you are
constructing with platinum, you may still need the old solders, since
they flow more easily than the plumb solders and leave nice bright
fillets in the seams, but use strategies in construction that
maximize contact and limit shear on these joints. If you are
constructing with platinum, the problem of melting temperature is
moot, since you’ll be using your own platinum which I would assume
you would buy as a known quantity, unless you simply tell the
supplier “surprise me”. As for palladium, which you won’t encounter
very often,
the color is a give away for the discerning eye, and if it’s rhodium
plated, that should raise your suspicions anyway. I’ll be watching
to learn something from this thread.
Hi , I will toss my two cents in here …Since we do not laser here [
yet :-)]…We have made a rule ; all generic stamped [ 950 or just
Pt / Plat] or unstamped , but is platinum . Are soldered when being
sized , with the .900 [ or “easy”] plumb plat solders ,[ we use
PM-Wests ]. When it is of our own manufacture , [we are using .952Pt
/ ruthinium for both casting and most fab work ] or is identified
900/100 pt/irid then we will weld/ or use .950 [ “hard”] plumb
solder as best suits the piece . This plumb solder is great , and
with this “rule” we have had no more unforseen melting incidents . I
still magnet test for cobalt alloy , but am not sure why [?] We have
found this plumb solder is "better "[color and strength] than
regular 1400 / 1500 solders that we would have used in the past .
Several posts have mentioned Palladium in the same context as
platinum , the lightness of palladium makes its identification
automatic [ at least after the first time you hold any ] its
almost half the "weight " of platinum , and is quite remarkable in
heft .
] its