I can see through a gem!

[m4816k]

Why I sometimes find gemstones through which you can see what's in the
background? For example, a blue topaz ring. You can see the skin of a finger
through the stone. It's even worse when there are very few facets, like in
an emerald cut. Is that low quality stone or something normal, and can it be
avoided? Thank you!

[Carl 1 Lucky Texan]

That observation is often assumed to be a normal look! Yet it, almost
always, indicates a poorly cut stone.
For each gem material there is a physical property called Refractive
Index. If a cut is not applied to the gem material at angles appropriate
for that specific substance's RI, there can be a significant reduction
in the overall appearance of a gem.
Most all intermediate to advanced books on Gemology or on Faceting
(gemcutting) will have a discussion of this area.
In general, if you can see the finger, or see text,etc. through a
gemstone held 'face up' that material is poorly cut. Note however that ,
the lower the refractive index (eg. ,opal, amethyst, aquamarine) the
more likely this 'windowing' will occur at even a slight tilt. rarely
would this happen with -say- CZ or diamond.
Occasionaly very dark garnets and perhaps tourmalines or other rough
will be cut with a shallow pavilion to allow windowing in an effort to
lighten the overall color.
hth
Carl
1 Lucky Texan

--
to reply, change ( .not) to ( .net)

[Linda Walsh]

The quality of the gem itself could be either good or bad; when you see
through the gem it indicates poor quality of the cut of the gem. It
means that the angles of the bottom facets are too shallow giving the
gem the wrong proportion of width to depth. Probably the cutter wanted
to make the outline of the gem as large as possible to LOOK like a big
gem, but the rough stone from which the gem was cut was insufficiently
deep to give the correct depth. If the gem material itself was good
quality, sometimes these stones can be recut to have smaller outlines
but appropriate proportions and can actually be much more beautiful and
valuable even though they are smaller.

[Dave Arens]

Hi,

>>Why I sometimes find gemstones through which you can see what's in
the background? For example, a blue topaz ring. You can see the skin of
a finger through the stone. <<

The reason it's possible to look through some faceted stones has to do
with the way the stone was cut.

Whether the stone reflects light from the pavilion facets when looking
into the stone from the table or whether it allows the light to pass
right through the stone is dependent on the 'critical angle'. If the
pavilion is cut below the critical angle, the light will pass through
the stone, the stone will be transparent. If the stone is cut above the
critical angle, light stricking the pavilion facets will be reflected &
the stone won't be transparent.

The critical angle is dependent on the refractive index (RI) of the
material making up the stone. The RI of stones varies from material to
material but is constant (within a very small range) for each material.
A piece of quartz has the same RI no matter where in the world it came
from or if its natural or synthetic. The same holds true for all other
materials.

The RI is one of the physical characteristics used in identifying gem
stones.

The RI is measured with a device called a refractometer.

Dave

[G N]

If its clean and glassy, its generally good quality material presuming its
genuine and preferable natural(not treated). The quality of cut is the most
important thing after quality of material. If you want something special,
only buy premium or custom cut stones, ie: many badly cut stones are from
Thailand or India, etc..... so beware. Some stones are cut to show clarity
and colour of the natural material only, as mentioned, low refractive
material. The Emerald cut was exclusivly designed for the Emerald, hence the
name, because it is more appreciated for its natural colour than its
refractive qualities. If you buy Emerald cut-type gems, buy them for the
colour of the material only, this would be my recommendation..... Eg: a
London-blue Topaz looks stunning with an Emerald cut while a Sky-blue Topaz
looks very dull.

Good hunting!!! :)

"m4816k" <marijan....@os.hinet.hr> wrote in message
news:9ap48v4pvkr9qmtfv...@4ax.com...

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