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A Cut Above
"In the state of nature, the surfaces of gems
are generally dull and lustreless; their shape
is irregular, and their mass is permeated by
flaws and imperfections".
Oliver Cummings Farrington (1864-1934), Gems
and Gem Minerals.
While it would be wonderful if gemstones came
out of the ground ready to wear, this typically
just doesn't happen. Raw crystals from the earth
are usually called 'rough gemstones' (or just
'rough') and this is actually very apt - rough
gems can look pretty rough!
Lapidary (gem cutting) is thousands of years old
and is the transformation of raw crystals into
dazzling gemstones. It is the art of making the
gem assume a certain shape, unlocking its lustre,
colour and brilliance. Lapidaries, also known as
gem cutters, have two general styles they can
choose when cutting gemstones:
- Faceted Gems: Gems with geometrically-shaped, flat polished
faces. Today, faceted gemstones are the most
popular style, but this was not always the case.
Big fans of cabochons, cameos (a gem carved in
positive relief) and intaglios (a gem carved in
negative relief), did you know that ancient
Romans considered wearing faceted gems vulgar?
Non-faceted:
- Non-faceted: Gems that don't have geometrically-shaped,
flat polished faces, such as cabochons. Derived
from the old Norman French word 'caboche',
meaning head, cabochons are an ancient shaping
and polishing technique that remains popular
today due to the yesteryear charm and character
of what are typically, richly coloured gems.
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The different parts of a gemstone. Due
to the spherical nature of most rough,
the oval is the most common shape for
coloured gemstones as it typically best
balances beauty and weight retention |
Because of their different optical properties,
coloured gems do not have an ideal 'brilliant
cut' like Diamonds (see the diagram in this
section for more). Which style, cut and shape
lapidaries select depends on the type, shape and
quality of the rough gemstone. The cut of a gem
directly affects its overall value as the cut
determines how well a gem returns its body
colour back to the eye.
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Classic gemstone shapes and cuts |
The lapidary frequently performs a juggling act
between beauty and commercial considerations,
such as carat weight retention. For every gem,
the lapidary is looking for the best compromise
between appearance and size, remembering that
the value of the finished gem also depends on
its carat weight. Maintaining a gem's critical
angle (the maximum angleof refraction,
click here for more) often unavoidably results in a
smaller gem. If you accept a little bulge in the
pavilion, the gem mightn't have its very best
brilliance, but will weigh more. You also have
to consider the impact of windows (areas of
washed out colour in a table-up gem, often due
to a shallow pavilion) or extinctions (areas of
darkness in a table-up gem, all gemstones
possess some degree of extinction) on a finished
gemstone's beauty. At times, making these
decisions is extremely difficult and better
suited to a soothsayer than a gemstone
professional. For example, several years ago, I
encountered a beautiful Canary Yellow Sapphire
in my adopted hometown of Chanthaburi, Thailand.
At over 35 carats with excellent colour and
clarity, it was a very special gem of
exceptional rarity. The only minor critique
would be that some of its cut proportions were a
little loose, ever so slightly reducing its
brilliance. Now you could have re-cut the gem,
tightening things up to achieve 'optimum
brilliance', but this would have reduced its
weight by at least 5 carats - not a decision for
the fainthearted! Sometimes size does matter and
big can be beautiful, but this isn't always the
case. Beauty will sometimes be sacrificed to
minimise rough weight loss and vice versa.
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The round brilliant cut possesses
the angles and proportions once thought
necessary to display a Diamond's best
dispersion (fiery flashes of colour),
scintillation (play of light) and its
characteristic brilliance (white light
reflections). While also used for other
gemstones, the brilliant cut was
developed specifically for Diamonds. The
standard number of facets in a round
brilliant cut is 57 (or 58 if you
include the culet). The brilliant cut
was developed by several people,
including Vincenzio Perruzzi (an
18th-century Venetian cutter), Henry
Morse (he opened America's first Diamond
cutting workshop in Boston,
Massachusetts in 1860) and the Russian
mathematical genius Marcel Tolkowsky (a
member of a large and powerful Diamond
family, he calculated the cuts necessary
to create the ideal round brilliant cut
in his book, 'Diamond Design' published
in 1919).
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The steps in cutting are slicing (also
sometimes confusingly called 'cutting'),
pre-forming, shaping and polishing. The
first step involves using a
Diamond-tipped circular steel saw to
slice the rough into pieces. Once the
rough has been sliced, it is pre-formed
using a vertical steel grinding wheel.
The shaper then uses a hand-operated
shaping wheel to more accurately present
its facets and size. The final step is
polishing the gem with Diamond paste on
a horizontal wheel to reveal its hidden
lustre and brilliance.
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That's all well and dandy, but how do you tell a
good cut from a bad one? No one cut is always
more beautiful than another, it's all down to
the magic of nature and the artistry of the
lapidary. One thing that can confuse is shape
versus cut. Sometimes they mean the same thing
(a 'princess cut' is always square in shape) and
sometimes they don't (a 'step cut' can be
square, rectangular or octagon). Like most
gemstone authors, I am not too puritanical about
this, using both terms interchangeably as
appropriate, but the cut is not just a
gem's shape, it is also the cutting techniques
(facet arrangements, finish and proportions)
used to finish the gem from the rough. A gem's
shape will affect the overall look of the gem,
but if it's faceted properly, the shape won't
necessarily affect its value. Saying this,
certain shapes will sometimes demand a slight
premium or be marginally discounted depending on
the gem type and the amount of rough lost or
retained to arrive at each shape. A diagram of
some of the classic shapes and cuts are included
in this section. Due to the spherical nature of
most rough, the oval is the most common shape
for coloured gemstones, as it typically best
balances beauty and weight retention. Once
you've established your shape preference, simply
use the following checklist:
- Even, uniform colour with no distinct zoning,
unless of cause this is a feature of the
gemstone as in bicolour varieties. Remember,
gems are designed to be viewed from the table
down.
- Balance, symmetry and proportion. Some 'fancy
cut' gems are deliberately cut asymmetrically,
but this is by no means standard. Fancy cut gems
are either standard cut variants, create the
illusion of a bigger more perfect gemstone, play
with the natural shape of the rough or are
revolutionary new shapes, made possible by
advances in cutting technology.
- Acceptable crown height and pavilion depth. The
crown is usually one-half to one-third the
pavilion depth.
- Acceptable brilliance, remembering that
brilliance varies amongst different gemstone
varieties. Some books suggest always looking for
a 'lively gem', but if the species is not noted
for its brilliance, this can be misleading.
- Acceptable clarity (amount and location of
inclusions), again remembering that acceptable
inclusions vary among the different gem
varieties.
- A good polish condition, with no
eye-visible scratches or polishing marks.
- Acceptable pavilion bulge and girdle thickness.
- Acceptable sharpness of the facet junctions.
- The majority of the gem's weight is visible from
the top.
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The diagram below and opposite shows
gemstone cuts from antiquity to the
present. True 'artists in stone',
lapidary has evolved over thousands of
years. During antiquity, cabochons were
initially the only cutting style
available. Guided by the natural facets
of the gemstone's crystal structure, the
lapidary cut gems in increasingly more
complex ways over time. The earliest of
these involved removing the tops of
crystals. In the last hundred years,
technological advances have allowed
cutters to develop some breathtaking
innovations. New cuts such as the Wobito
Snowflake™ would have been difficult,
if not impossible, to create just 200
years ago. The general perception is
that faceting lower quality rough is not
economically viable. When I first
started in the gem business, I assumed
only lower quality rough was cut 'en
cabochon', but this is not the case.
Individual preferences vary and today,
fine quality gems are cut in both
styles. Please don't make quality
assumptions based solely on whether a
gem has been faceted or not. |
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