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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: Gems that don't have geometrically-shaped, flat polished faces, such as cabochons. Derived from the old Norman French word 'caboche', meaning head, cabochon is 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). 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 angle of 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 gripe 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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