Hi All!
I have a platnium question. I have an old mine cut diamond in a
platnium bezel and would like to solder it right on to a platnium
ring I am making. Do you think the diamond can withstand the heat
from melting my 900 platnium solder right next to it??
Thanks,
Rebecca
Hi Rebecca, There is no platinum solder you can use next to a
diamond, or any other stone. Use white gold solder or pull the
stones.
Take care. Tom Arnold
Platinum solder is too hot for a diamond. It will likely frost,
requiring you to demount the stone and have it repolished. Your best
bet is to use 20K white welding solder. Rhodium if the seam shows.
Other white gold solders will work but the 20 is whiter and
stronger.
Because this old miner is mounted I assume it’s breakout from a used
piece, you must get it scrupulously clean first or wind up with a
black/brown diamond. Hot lye followed by ultrasonic and/or steam. You
want to reach the girdle which is covered by the bezel. And just for
added safety firecoat the diamond, which hopefully gets any residue
the cleaning missed. I like handi-flux but probably others would work
as well. The idea here is the flux melts and ‘captures’ the dirt,
keeping it away from the surface of the stone. This only works with
diamonds. While you can (usually) heat corundum any flux present will
etch the surface.
No fire coat I am aware of will protect diamond from burning at
2730 F (flow point of Hoover and Strong 900 plumb pt solder). I have
successfully soldered parts with diamonds in place up to 1500 F. I
confess I have damaged a diamond while attempting to work at a
higher temperature. 
David Lee, CMBJ
Hi Rebecca;
You might get away with it, but that’s mighty close to the
temperature needed to “smoke” a dimamond, that is, burn the surface
such that it has to be re-cut at significant expense. I’d suggest
gold solder, but the bond is not great. For that matter, neither is
that of a 900 platinum solder. Laser welding would work, as long as
you got significant penetration of the weld. If you can burnish back
the bezel without chipping the diamond, you could use a platinum
plumb solder, but be warned, old mine cut diamonds are notorious for
having razor sharp girdles, so they chip easily. Can you cut or sand
away the bezel around the stone and get a new bezel? It might be
worth it.
David L. Huffman
If possible, take it to someone with a laser who does trade work.
Much safer in every regard,
Judy in Kansas
While the temp. required to do any platinum soldering is too high
for diamond, it is possible to attach a preset stone, diamond or
other, using the laser to weld it in place.