Gemstone Cuts: Shapes and How to Choose

Cutting a gemstone means giving it shape, proportions and facets to reveal its colour, brilliance and play of light. The facets guide light into the heart of the stone, then return it to the eye: this is how brilliance, depth and that “life” that seems to animate it are born. The lapidary works like a sculptor — releasing a silhouette hidden within the material, whether it is a sapphire or a tourmaline.

It affects both beauty and value. A cut that is too deep or too shallow lets light escape: the stone appears dull, even if it is pure and well coloured. A skilfully executed cut, on the other hand, offers crisp brilliance, regular scintillation and inner clarity.

Between two otherwise identical stones, the difference is immediately apparent: one lights up, the other fades. It is the only one of the four grading criteria that does not depend on nature, but entirely on the human hand — and it is also the one you can judge for yourself, with a little practice.

The choice of shape also depends on the hand that will wear the ring — our guide on which finger to wear the engagement ring sets out what each body type calls for.

This is where the essentials are decided, and the reasoning is not the same as for a diamond. There are two families of cuts, which do not serve the same purpose.

Hence the practical rule: with a coloured stone, it is the colour that dictates. A sapphire of deep blue benefits from a cushion or oval cut, which show its hue in volume. A emerald of great clarity deserves a step cut that reveals it; a heavily included emerald, by contrast, will be better served by a brilliant cut.

One final point that only the lapidary masters: many coloured gemstones are pleochroic — they do not show the same colour depending on the crystal axis. The cutter must orient the stone so that its finest hue faces forward, even if this means sacrificing weight. It is an invisible trade-off in the finished result, and it makes all the difference.

The carat measures weight, not size. It is obvious once stated, and yet almost everyone buys as though the two were the same thing.

Yet gemstones do not have the same density. At equal weight, a dense stone occupies less volume — it therefore appears smaller when viewed from above.

Practical consequence: a one-carat sapphire appears smaller than a one-carat diamond, and a one-carat emerald appears larger than both. This is neither a flaw nor a scam — it is physics.

Unlike authenticity or treatments, cut quality can be assessed with the naked eye, with a little attention. It is the only criterion you can evaluate yourself.

• Symmetry. Look at the stone face-on: the two halves should mirror each other. A marquise whose points are not aligned, a heart whose cleft is off-centre — these become immediately apparent once you know what to look for.
• Facet alignment. The edges should meet cleanly. Facets that cross at odd angles betray hasty cutting.
• The absence of a “window”. This is the most common flaw in coloured stones: a cut that is too shallow lets light pass through instead of reflecting it, and a pale, lifeless area appears at the centre. Place the stone on printed text: if you can read through it, it has a window. The opposite flaw — a stone that is too deep — creates dark areas and a dull gem.
• Liveliness. Move the stone slowly under a light: the sparkle should travel across the entire surface, with no area remaining lifeless.

A shallow cut is almost always an economic choice: it preserves weight. The cutter has favoured carats over beauty. Well cut, a fine stone — sapphire, rubellite, tourmaline — will have as much presence as a diamond.

Cutting combines tradition and technology. Historically, the gem cutter used discs coated with diamond powder; today’s workshop combines these traditional tools with precision machines that ensure consistent angles, from preforming to polishing.

The hand remains decisive. A few fractions of a millimetre change everything. The gem cutter observes the orientation of inclusions and the distribution of colour, then weighs up carat weight and beauty — a judgement no machine can make in their place. Each facet is polished patiently, down to the final touch that creates that crisp brilliance.

Scientifically, it all comes down to refraction: light enters through the table, bounces off the pavilion facets and returns to the eye if the angles are right. The more precise they are, the more light returns — and the more fire the stone has.

But cutting is also an emotion. A heart evokes romance, a cushion softness, a princess cut modernity, an emerald cut classicism. The shape you choose says something about you — and about the way you wish to wear light.