This provoked some questions on my part, and I sent him the
following email. Jurgen is apparently too preoccupied to reply at
the moment, so perhaps some Orchid members would like to comment on
the issues.
Riccardo, your question to Jurgen pretty much summed up the state of
affairs. In fact, there’s yet another potential source of trouble, and
that is the fact that the coefficients of thermal expansion (COE)
differ between gold alloys nd (including solders) and platinum. so
joints made with gold solder to affix platinum parts are already
slightly strained once they cool. As you note, there is little
penetration of the platinum by the gold solder, so that though the
platinum is “wetted” by the gold solder, it’s not penetrated much, if
at all. The result is generally a bond which, if stressed a lot, will
fail more quickly than the same bond made between gold parts with the
same solder, or platinum parts made with platinum solder.
But it’s not quite as “cut and dry” as that. Consider the
traditional platinum solders too. While the highest melting of them
do approach platinum’s melting point, and contain some platinum, the
lower, safer grades, are mostly palladium and silver, and melt enough
below the melting point of platinum that they too, don’t give a good
penetrating bond. Try soldering some platinum wires to a platinum
part with 1100 solder, then try pulling them off again with a pair of
pliers. You’ll be surprised at how easy it can be to just peel off
the wires. The higher melting platinum solders do a lot better, and
the new, plumb platinum solders, despite their relatively safe melting
points, also seem to give much stronger joints.
But when we’re retipping prongs on diamonds, not to mention other
gems which can withstand even less heat than diamonds, we’ve got a
major problem. Diamonds simply cannot withstand the heat needed to
use even the easiest melting of the platinum solders without major
risk of burning the stone. while I’ve now and then used 1100 or even
1300 solder grades to solder fairly close to a diamond (melee. I
don’t risk this with bigger stones), and sometimes can get away with
doing so as close as a millimeter or two from the stones if I get in
and back out real quick, with lots of boric acid on the stone, it’s a
big risk, and I burn some stones doing this. The resulting repairs
may be better than if I’d done them with gold solders, but I also end
up having to replace burned melee about a third of the time. Were I
trying this with actual retipping tasks, I doubt I’d get away with it
at all, ever.
So IF you’re going to be retipping the diamonds in platinum prongs,
you’ve simply got no choice but to use gold solders, simply to get
within a safe melting point of solder. Yes, it’s not as strong a
joint as one would like. But platinum is malleable, wear resistant,
and strong stuff. If you’ve prepared the joint well (the existing
prong surface is flat and clean, and well fitted to the added piece,
you’ll find that though the joint may not be optimal, it will hold up
well enough. In fact, putting platinum tips onto gold heads when
retipping holds up better than putting gold tips on, simply because
the new tips in platinum will wear so much better than new gold tips,
even if the solder joints holding them on are less strong. Of course,
in doing this, the different metal on the tips is visible. But
usually not objectionable visually.
The conclusions to draw are several. You can retip platinum prongs
using platinum soldered on with gold solder, if this is the proper
repair to be making at all. Doing so is actually standard practice
much of the time. But it will be a superior repair if you can unset
the diamond, retip, or better, rePRONG it, not retip it, using all
platinum metal and solder both. Or use a new head entirely.
And of course, if you happen to have a piece that really needs
retipping and cannot be repronged, yet you’re not comfortable with
adulterating the piece with gold solder, you’ve now got an option that
didn’t exist until a few years ago. Laser welders can safely fuse new
platinum onto a platinum head, even with relatively heat sensative
stones, like emerald. I’ve seen successful retippings in platinum
done even with Opals (!) using lasers. If you don’t have a laser
yourself, you can always opt to send the work to a shop that does
have one. There are several firms which now offer that service. It
does cost more, but if the jewelry is worth it, then the resulting
repair can be far superior.
Hope this helps.
Peter Rowe