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Porosity on 18kt white gold


#1

dear all can you help how could i fix porosity on 18kt white gold
pieces which are already set with 2 to 3 carats of tapper diamonds.
any advise here would be of great help

kumar


#2

Hello Kumar: Porosity in 18K white gold. Is it Nickel white?
Burnishing the surface smooth is very difficult if not impossible as
you will probably wind up with a bunch of polish lines. I have had
problems with porosity in white gold off and on in the past and what
I usually do after I cast is clean up areas on the item all the way
to a polish to see if I got porosity before I go any further with it.
If the porosity is localized in one spot like the shank you can cut
away and replace that section but if it is all over you might try to
talk the customer into a brushed finish instead of high polish.
Michael R. Mathews Sr. Victoria,Texas USA


#3

The only way … is the use a laser welder. If you know anyone who
has one it can be done very quickly… Did anyone come to the Stuller
workshop last weekend? If so what did you think

Andy “The Tool Guy” Kroungold
Sales/ Tools and Technical
Stuller Inc.
337-262-7700 ext. 4194
337-262-7791 fax
andy_kroungold@stuller.com


#4
  The only way .. is the use a laser welder. If you know anyone
who has one it can be done very quickly.. 

And even the laser sometimes has it’s problems, partly depending on
how old the laser model is. Older models, without pulse shaping or
pulse shape optimization, sometimes seem to just move the bubbles
(pits) around a bit, instead of always filling them it. Yes,
eventually it works, but it can be more difficult than one would hope
in cases of serious porosity. And then there’s the problem of weld
cracking in these harder white golds. Again, this tends to be more a
problem with the older model lasers.

One tool I sometimes have to fall back upon, or combine with laser
welding, is the old “bent bur” burnisher. That’s an old bur, the
working end of which has been removed, and the stub (or use the back
end of the bur to make it) heated and bent over into a short L shape,
and the little dog leg end highly polished in a convex shape. I
actually solder a little bit of carbide to the end, and polish that
to a hemisphere with diamond compound. The lower “friction” of
carbide makes a much better burnisher. Anyway, this tool goes in a
flex shaft handpiece, and at moderate speed, the little dog leg
rotates, and can be used as a power burnisher, almost a hammer with a
wiping motion. white golds are hard enough that burnishing porosity
with a hand burnisher is difficult, but the rotary burnishers like
this are aggressive enough that you can get some effect. If you’re
careful, work the surface in a couple directions, and then don’t
over polish, you can get a good looking surface. Of course, this is
only a surface fix. Any underlying porosity in the metal is still
there.

Porosity in white golds remains a problem for us too. At least
you’re not alone. Sometimes, the best fix, at least if the piece is
a production casting from a wax injection, is just to scrap the
piece and recast it from another wax model. Pay close attention to
where you put the sprues, and to casting temperatures. Both have a
big effect on porosity. You’ll find it productive after casting to
first finish the casting and polish it before any additional
fabrication (adding prongs, etc) or stone setting takes place. That
full prepolishing step will let you detect and fix porosity, or
decide to scrap the piece and remake it, before you’ve put a lot of
work into it.

Peter


#5

About the porosity on 18 kt white gold, when you cast gold, it can
have a skin that you have to get through that looks like porosity,
but if you go down far enough, it goes away. It looks like pits in
the metals. porosity is where you cannot see the pits, and it won’t
take a polish.Richard in Denver