All: I recently fabricated a ladies platinum engagement solitare
ring with a trillion diamond of approx. 1.5ct. I carved the wax
and it was sent out for casting since I can’t cast in platinum.
I also smithed a wedding band to fit and soldered them together
before setting the diamond. The customer was very satisfied with
it. However, upon 2 return visits for cleaning, each time I’ve
noticed the stone to be rather loose. It’s in good heavy metal
and setting up fairly high in “V” prongs at each corner, the ring
in a sort of twist design. Of course, I’m very concerned about
this. Could it be that the metal is too soft and needs to be age
hardened? If so, could you suggest a method to do this or
perhaps another solution to the problem?
Platinum alloys, for the most part, are much softer than gold
alloys so pieces made from platinum must be substantially thicker
to have the same strength. Remember that the force required to
bend something increases linearly as the width (perpendicular to
the applied force) of the piece increases, and exponentially with
thickness (parallel with the applied force). The mistake I often
see is that people make platinum prongs the same thickness and
length as gold, and they just don’t hold up. Reducing the length
overall or effectively with an underbezel reduces the torque of
an applied force as well.
e-mail me off list if I have been unclear in any (every?) way.
JA - Certified Master Bench Jeweler
PS - I studied Physics in college
Steve, I think it’s been mentioned, several times in Orchid in
various threads, that ordinary platinum alloys cannot be age
hardened. You can work harden it, and since platinum anneals
somewhat slowly, it’s even possible to assemble parts without
annealing, especially if gold solders are used, since platinum
anneals well above the melting point of gold solders. With
platinum solders, you can’t quite preserve all the hardness,
usually, but you can, if you’re fast enough, keep some of it.
Generally, though, the real solution is that you cannot design
settings to be made in platinum with the same parameters as you
would in white gold. high V prongs just don’t work so well in
platinum, unless they are much heavier, or the head is fitted
with an undergallery to brace the prongs in position. While
platinum bends easily (and the problem is that although other
metals flex too, they spring back, while platinum does not,
leaving the stone loose), it’s actual strength, in terms of
breaking or stretching, etc, is very good. so the undergallery
can be made of fairly thin wire, and kept unobtrusive. the stone
then almost sits on the undergallery as well as being held in the
prongs or chevron tips (whichever you’ve used). The main role
for the undergallery here is not to actually support the stone,
though in doing so, it increases the stones security. The main
role is to keep the prongs from spreading apart or bending. Even
if the wire is thin enough to itself be easily bent, it won’t
stretch without considerable and unlikely stress, so once the
diamond is set and everything is essentially, in a state of
slight tension, the result is a setting that will not loosen for
a very long time.
Hope this helps.
whoa! this is only true with some alloys of plat, but not all.
plat / cobalt, in particular, can be very rigid and work
hardens very quickly. with a little planning, you can work plat
into your designs and keep things light. long, thin prongs are
gonna bend, no matter what the material.