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Finish behind stones


#1

Which do you feel is a more effective finish to put behind a dark
faceted stone (in this particular case its pyrope in platinum)…rough
cut, satin, or bright polish? Or doesn’t it make a difference? The
pavilions will be shrouded but there will be a hole for cleaning.

I like to pick nits sometimes.


#2

The first thing I do when looking at a piece is to check the back. A
clear lack of concern about quality here is a pretty good indication
of the level of care in the entire piece. For your ring I’d tend to
polish but whatever you choose make sure that it looks deliberate.

Jeff


#3

Jeff,

oopsies, I should have been clearer. I’m not talking about the back
side of the mounting. My concern is to maximize reflection back into
the stone, from the pavilion side.

At first thought it might seem that a high polish would reflect the
most light but I’ve noticed it is somewhat selective in what
direction light is reflected. I was wondering if a rougher finish
might disperse available light more evenly.


#4
oopsies, I should have been clearer. I'm not talking about the
back side of the mounting. My concern is to maximize reflection
back into the stone, from the pavilion side. 

I was sure you’d get a slew of people saying this, so I didn’t…
though I feel sure you know this, so maybe I’m not understanding
something. With a well-cut stone, the light coming out the front all
came in the front. It shouldn’t make any difference whether there is
any light behind it or not. It should make even less difference
whether the setting is polished or not on the inside. Now, if the
stone is windowed, that’s another matter. I think polished is
better.

Noel


#5

Hi Jeff/Neil. (I missed the earlier part of this).

The more polish behind the stone the better. You have at least a
chance of brightening it up with rhodium. You have no chance if it
is dull. In a few weeks the rough metal will have dirt stuck to it
and they won’t be able to clean it off but it will clean easily if
it is polished. It might help reflect light, but mainly if the stone
is shallow.

Phillip


#6

Hi Neil, I will almost always polish the area behind a center stone.
Unless a stone is opaque, the light bouncing around will help. And
besides, it looks better from the back.

Have fun. Tom Arnold


#7

Noel, I believe that this is true primarily for diamonds.

Andy


#8

Hi Neil,

My concern is to maximize reflection back into the stone, from the
pavilion side. 

The way to maximize the light return from the pavilion of a stone is
governed by the laws of physics & the refractive index (RI) of the
material that the stone is made of.

There’s a angle called the ‘critical angle’ (CA) that’s dependent on
the RI of the stone. The higher the RI of the material, the lower
the CA. If the pavilion of the stone is cut at an angle greater than
the CA any light striking a pavilion facet cut that way will go
right out the back of the stone. To reflect it back into the stone,
the facet must be cut at less than the CA. Because most faceted
stones don’t remain in one position, when the stone is tilted, the
apparent CA to the viewer changes & this causes loss of brilliance
in a stone. The best way to minimize this is to cut the pavilion a
degree or more below the CA.

Dave


#9
Noel, I believe that this is true primarily for diamonds. 

I don’t wish to beat a dead horse, but in my study of faceting, the
process is all about cutting the stone at the proper angles to bounce
the light around inside and back out the top. Light from the back,
if visible, tends to obscure the “sparkle” the faceting creates, just
as light shining in through a window will prevent you from seeing
your reflection off the inside.

The higher the refractivity of the stone, the more brilliance it can
have, if properly cut, so diamonds do this very well and quartz
somewhat less so, but the principle is always the same. Very dark
stones may be cut at the “wrong” angle to allow more light through so
they appear lighter, at the expense of brilliance. “Windowing”,
where some facets at the culet are too shallow, allows light directly
through-- a flaw in the cut. Most of the time in jewelry there isn’t
much light available from the back, except maybe in earrings, so the
window will look dark, not bright, and may show the color of the
metal through, so if this is yellow gold, it may make the stone look
muddy or “off”.

Likewise, gluing a stone in tends to negate the effect of the
pavilion facets, making the stone dull-looking by allowing the light
to leak out the back.

OK, got a little carried away there, but I figure it is better to
offer reasoning and that to just say “Does not!” “Does
too!” ;>)

Noel


#10
but in my study of faceting, the process is all about cutting the
stone at the proper angles to bounce the light around inside and
back out the top. Light from the back 

Noel, all of what you say is essentialy true, and there’s another
post today about RI and critical angle. The problem is that the
majority of stones today are diamond cut or nearly. For an aquamarine
to be cut respecting it’s RI would be something very different - I
don’t know the math on it, but it wouldn’t be diamond cut. I think
people like, and expect, those proportions in any stone. Meaning that
MUCH light in a citrine, for example, is coming through the back and
even the girdle. I also think this whole thread is to some degree
(not the RI part, the metals part) pedantic. Any variation in the
finish behind a set stone, unless it’s really “glassy”, is going to
give infinitesimal results in the apparent look. My solution is
simple - don’t have a back, drill the hole to 80% of the stone width,
which is more proper anyway. One simple test for a (round) CZ,
besides just looking at it, is to turn it upside down over some
newsprint or something. You can see the print through the CZ, but not
a diamond. A graphic illustration of the importance of RI.

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