Back to Ganoksin | FAQ | Contact

Cracks in platinum


#1

I had a customer today with a solitaire platinum engagement ring
which she had made to order in Dubai in January 2010.

It has a large crack in the mounting visible to the naked eye. Do
you have any advice as to how this could happen?

Thank You
Julie


#2

Hi Julie,

If this is a cast piece, there are several different causes for
cracking in a platinum casting. A dirty or contaminated crucible,
contaminated metal which can be caused by using too much old metal
(when casting gold and silver you can use 50% old metal, but for
platinum, that’s just asking for cracks), an overly oxidizing casting
flame (may be caused by using a torch that is too small), use of
acetylene as a casting torch fuel, or getting traces of steel or
other metal in the wax model, the casting metal or the crucible.
Other causes can be a temperature that’s too low for either metal or
flask, a temperature that’s too high for either flask or metal
(although that’s not likely), improper gating, a centrifugal casting
machine that accelerates too slowly or quenching the casting too
soon after breaking it out.

The two most likely causes of cracks in a platinum casting though
are either contaminated metal or the metal temperature at casting was
too low.

The worst news is that when there is one crack in a platinum
casting, there will be more, almost guaranteed.

If it is a fabricated piece or is assembled from die-struck parts
the most likely cause is contaminated metal, possibly caused by using
steel soldering tools for assembly, with over-working between
annealing being a distant second possible cause.

Platinum and steel don’t play well together.

Hope this answers your question.
Dave Phelps


#3
I had a customer today with a solitaire platinum engagement ring
which she had made to order in Dubai in January 2010. It has a
large crack in the mounting visible to the naked eye. Do you have
any advice as to how this could happen? 

The platinum used in the mounting may be contaminated with an
incompatible metal or silica or carbon but it is really impossible
to even guess with any accuracy without seeing it.

James Binnion
James Binnion Metal Arts


#4
It has a large crack in the mounting visible to the naked eye. Do
you have any advice as to how this could happen? 

A couple possibilities.

One might be a bad casting, if the ring was cast. Platinum can
present some difficulties if not cast correctly, including sometimes
rather dramatically sized shrinkage cavities which can weaken those
portions where they form. And cast platinum can have a very coarse
crystal structure (large crystals). In some cases, especially with
contamination of the platinum, the crystal boundaries can crack under
stress.

Another possibility is if the ring was built with a laser welder,
and not used correctly, or with an incompatible platinum alloy. While
most platinum laser welds very well, you can sometimes still get
cracks in the welds if you are welding flawed metal, or over a poor
solder seam, etc. Unlikely, but possible.

Another likely situation is simply that the ring was made with
platinum that had become contaminated. There are a number of things
that can be accidentally introduced to the platinum that can make it
brittle, either over the whole mass of metal, or in localized areas.
Platinum has a number of “rules” to follow when working it, which if
not paid attention to, can get a platinum smith (usually a novice
one) into trouble.

It may also be simply that in the making, that section of metal was
worked too much. Platinum can take a lot of working, more than most
other jewelry metals, but it too has it’s limits. If bent too often,
or stretched and stressed too much, it can form cracks. I’ll bet the
crack in your customer’s ring was already at least started there when
it left the shop, and has just grown bigger under the stress of use.

I would also bet that in most cases, a crack like that can be
properly repaired by any decent platinum smith unless the whole ring
is seriously flawed. Laser welders make that kind of repair pretty
easy, but even without, it’s possible in most cases. Sometimes stones
have to be removed first, but again, that’s easier to do with
platinum than with, say, white golds.

HTH
Peter Rowe


#5
It has a large crack in the mounting visible to the naked eye. Do
you have any advice as to how this could happen? 

In one sentence - carbon contamination. Several way it could happen.
Soldering on charcoal, incorrect flame, and etc…

Leonid Surpin
www.studioarete.com


#6

Hi Julie,

Cracks in a cast platinum mounting can happen for a variety of
reasons, and most of the time you will not be able to diagnose the
cause without destroying the mounting. Lasering the crack for repair
may give indications as to the source, as common contaminants such as
silica or flask material will cause the laser to flash a blue or
brown color. If the metal does not discolor under the laser, then the
possibility of sub-surface gas or shrinkage porosity may be the
cause. You can’t see this without exposing the fracture surface, and
that usually destroys the ring.

Aside from contaminants or sub-surface porosity, another cause of
cracking is excessive cold-working of the metal. This may occur from
hammering to size up or the use of a ring stretcher. The more we
cause the molecules to move and create dislocations, the harder and
more brittle the metal becomes. Lastly, there can be residual stress
from solidification of the molten metal. This is fairly rare in
platinum, but I have seen it happen a number of times. Of all these
causes, the contaminants are the most dangerous as the entire ring
may be brittle, and over time other areas may start to crack.

I would put the ring on the mandrel and try to bring out more cracks
with a leather mallet. If this doesn’t bring out cracks, then you
probably have overall healthy metal with a localized defect that can
be repaired. If this is the case, create a v-notch all the way around
the crack (both inner and outer diameter) and fill with Pt laser
wire. Make sure you go very deep and you should have a robust repair.

One last thought. since this was made in Dubai the alloy may be
something we are not familiar with here in the states. There are
plenty of alloys out there and some are more brittle than others.
This one may be difficult to track down unless they reveal it in the
stamping.

Good luck!
Teresa Frye
President
TechForm Advanced Casting Technology, LLC
503-652-5224


#7

Where precisely is the crack? A dry soldered joint will give way if
it’s bent, and a poor laser-weld will do the same - both are easy to
fix with the right equipment. If the cracks are very fine, and cover
a large area, it will be a lot harder to sort out - there might be a
problem with the alloy, or with the way the ring was manufactured,
and no amount of soldering or welding will resolve it; scrapping the
mount and replacing it would be the only option.

Jamie
http://www.primitivemethod.org