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Sizing mounting

If a ring mounting to fit a stone’s measured size is not available,
is it better to go for the next larger or the next smaller head size?
(Round brilliant.) How close should the measurements be to get a
proper fit?


Pam Chott

I usually err on the side of a slightly larger head. It seems that if
I use a slightly smaller size, the combination of having to increase
the diameter ( bend the prongs outward) and grind a little more metal
reduces the “grip” of the prongs. Rob

Hi Pam,

That depends on the cut of your stone and the style of the mounting
itself. For instance in a bezel mount clearly the width of the stone
cannot exceed the width of the bezel walls (grin). My biggest
consideration on this question is the belly of your stone - if it’s a
deep, round native cut belly, go larger (for prongs anyway). I think
we’ll need more specifics to properly advise you on this one.

Mike Rogers

Hi Pam; I always try to get a head that is listed in the catalog as
the exact size as the stone (I use Stuller and some others). If I
can’t get that, I always defer to the larger head and here is why.
When you bend prongs in to meet a stone, you may have more difficulty
setting the stone level, but your worst problem is only an aesthetic
one. The prongs curving up to the girdle tend to make the stone look
smaller from the side. Bend them in a bit first, then cut the
notches, not the other way. If you have to splay the prongs out, you
will have to bend the prong in more severely at the point where you
notch it, which stresses white gold, if that’s your choice. It also
makes for a setting wherein if the stone is struck on it’s table, it
will lever the prongs downward and outward, thereby loosening the
stone. This problem is even worse with platinum. I don’t like a
head that is more than 1/2 a millimeter larger than it is supposed to
be. That is not always possible with stones in 2 carat and over
sizes, especially in platinum, which is what I prefer for anything
over 1 carat, as I don’t like 6 prong heads and 4 prong white heads
are too risky. Yeah, I know all the tricks for minimizing prong
shear, but I still prefer to put a $6000 stone in a platinum head if
it only costs me and the customer another $35. Now here’s a trick
for you.

My thanks to Mike, Rob and David for their suggestions and remarks
concerning choosing the appropriate size mounting when the customer’s
stone doesn’t perfectly match the sizes available.

The client’s diamond (round brilliant) was his mother’s and he was
selecting a (Stuller) mounting for his fiancee’s engagement ring. As
it turned out, the mounting he picked has the center channel set
rather than in a head.

I really appreciate getting the rationale for one choice over another
and your generosity in sharing tips on making adjustments when
necessary. This is the kind of that really accelerates
the learning curve. This group is the best! This may be a well-used
sentiment but it is sincere!

For those who may be interested, I’ve just added a page of cabochons
to my web site:

As I am able, I will add to the stones offered and post my jewelry
gallery and shop as well.

Pam Chott