GEM FACTS AND STORIES.

Most coloured stones on the market are cut quickly near the mines, where the goal is to keep as much weight as possible. The result is often a stone with uneven facets, rounded edges, a thick or wavy girdle and a window in the centre that lets light leak out.

Precision faceting starts with a plan. Each material bends light differently, so the pavilion and crown angles are calculated for its refractive index. The stone is then cut on a faceting machine with an angle readout and an index wheel, facet by facet, until all meetpoints close in sharp, clean points.

Polishing is just as exacting. I move through progressively finer laps until each facet is flat and mirror-bright, with no scratches visible under a loupe. Crisp edges and a perfect polish are what give a precision-cut gemstone its lively sparkle.

The difference is easy to see in hand: a precision-cut sapphire, ruby or spinel shows even brilliance across its whole face, with no dead areas. That light performance is why precision-cut stones are chosen for fine jewellery and serious collections.

Sapphire and ruby, at 9 on the Mohs scale, call for diamond laps and patience. Emerald is hard but brittle, and many emeralds contain fine fractures that must be respected. Some materials, such as topaz, can split along a cleavage plane if a facet is placed carelessly. A faceter has to know all of this before the first cut.

The work happens on a faceting machine: a motor-driven lap, a mast with an angle gauge, and a quill that holds the stone on a dop. The stone is fixed to the dop with wax or adhesive, and later transferred so that the crown can be cut in exact alignment with the pavilion.

A large part of the job is judgement. Looking at the rough, the faceter decides where the colour is strongest, how to place inclusions, which outline the crystal allows and how much weight can be given up for better light. Two faceters can cut the same rough into very different gems.

When you choose a faceter, you choose those decisions. I cut every stone myself, from the first look at the rough to the final polish, so one person is responsible for the result.

Chromium does more than colour ruby: it also makes it fluoresce red. Rubies from the marble deposits of Mogok in Myanmar are low in iron, so this fluorescence adds a glow even in daylight. Today Mozambique is one of the most important sources of fine ruby, while iron-rich rubies from Thailand and Cambodia tend to be darker.

Most rubies are heated to improve colour and clarity, a long-accepted practice that should always be disclosed. Unheated rubies of fine colour are rare and carry a significant premium. Lead-glass-filled rubies are a different product altogether: their fractures are filled with glass, and they are worth a fraction of a natural ruby.

Ruby shows slightly different reds in different directions, so orientation matters. Before cutting, I look for the direction that gives the purest red and place the table accordingly. Many rubies arrive cut deep and lopsided to save weight; a careful recut can balance the proportions and reveal colour that was hidden in dark areas.

A well-cut ruby glows evenly from edge to edge, with no dark centre and no window. That is what makes a ruby worthy of high jewellery or a collection.

Famous sources shape the market. Kashmir sapphires, found in the Himalayas in the 1880s, are prized for their soft, velvety blue. Burmese sapphires are known for rich, deep colour, and Sri Lanka, historically Ceylon, produces bright, lively stones. Madagascar has become a major source in recent decades, and Montana in the USA produces sapphires in a wide range of colours.

Pink, yellow, purple, green and colour-change sapphires are also corundum, and the rare pink-orange padparadscha is among the most valued of all. Most sapphires are heated; unheated sapphires with a laboratory report command a premium, and other treatments such as beryllium diffusion must always be disclosed.

For the cutter, sapphire is a demanding and rewarding material. Its colour is often uneven, lying in bands or zones. By placing the strongest colour near the culet, a faceter can make the whole stone look evenly blue through the table. Orientation matters too, because sapphire can look violet-blue in one direction and greenish blue in another.

Sri Lankan sapphires in particular are often cut shallow, with a large window. A precision recut can turn such a stone into a gem that is bright across its entire face.

Emerald is 7.5 to 8 on the Mohs scale, but it is brittle and almost always contains inclusions and fine fractures. These inclusions, called jardin, are accepted as part of its character. Because of them, most emeralds are clarity-enhanced with oil or resin, which makes fractures less visible. Laboratory reports describe the degree of enhancement, from none to significant, and emeralds with no or only minor enhancement are valued much higher.

The emerald cut was developed for exactly this material. Its long step facets show off colour rather than sparkle, and its cut corners reduce the risk of chipping where stress would be highest. With a fractured crystal, it also helps the faceter remove weak areas while keeping a pleasing outline.

Cutting emerald needs restraint. Heat, pressure and vibration can open fractures, so I work slowly, keep the stone cool and plan the facets to stay clear of weak points. The same care applies to wearing and cleaning: emeralds should never go into an ultrasonic or steam cleaner.

A finely cut emerald combines deep, even green with a calm, clean face. Fine Colombian and Zambian emeralds remain a pillar of high jewellery and of serious gemstone collections.

Its recorded history reaches back to 14th-century Spain. According to tradition, Edward of Woodstock, the Black Prince, received it in 1367 after the Battle of Nájera. Henry V is said to have worn it at Agincourt. Today the stone, of roughly 170 carats, sits in the cross at the front of the crown, just above the Cullinan II diamond.

For centuries every red stone was called a ruby. Ruby and red spinel often grow in the same deposits, look alike, and both owe their colour to chromium. Only in the late 18th century did mineralogists show that they are two different minerals: ruby is corundum, an aluminium oxide; spinel is a magnesium aluminium oxide.

In the Middle Ages such stones were called balas rubies, after Badakhshan on today's border of Afghanistan and Tajikistan, where the finest spinels were mined. The Timur Ruby in the British Royal Collection has also turned out to be a spinel.

Spinel rewards careful cutting. It is singly refractive, so its colour looks the same from every direction, and its hardness of 8 on the Mohs scale allows crisp, sharp facet edges. A well-cut red spinel holds its own beside a fine ruby, even though it is still far less known.

Designers often work to exact dimensions. A centre stone may need a specific outline and depth to sit at the right height in its setting, while the smaller stones around it must be calibrated to a tenth of a millimetre. A precision cut makes this possible; a stone with uneven proportions forces the setter to compromise.

Pairs and suites are especially demanding. Earrings need two stones that match in colour, size, cut and light, so that they read as one design. A necklace or bracelet may require a whole series of stones graded in size yet identical in tone. Matching them often means cutting several stones at once from carefully selected rough.

Durability matters as well. A girdle that is too thin can chip during setting, and one that is too thick adds weight and spoils the look. In a precision-cut stone the girdle is even all the way round, the culet is centred and the facets are polished flat, so the setter can work safely.

I cut stones for jewellers, designers and private clients who expect this level of finish. A stone cut with precision can confidently be set in high jewellery or become the centrepiece of a collection.

Rarity drives value. The key factors are colour, clarity, size, origin, treatment and cut. A fine unheated ruby or sapphire of several carats, with strong and even colour, is far rarer than a heated stone of similar appearance. Origins such as Kashmir, Burma or Colombia can add a premium when a respected laboratory confirms them.

Documentation is essential. An investment gemstone should come with a report from a recognised laboratory such as GRS, Gübelin, SSEF, GIA or AGL, stating its identity, its treatments and, where possible, its origin. Without one, a stone is hard to value and hard to resell.

The cut is often underestimated. Certificates rarely grade the cut of coloured stones, yet a well-proportioned stone with even light and a clean face is more desirable to the next buyer. A precision cut can make the difference between a good stone and a truly exceptional one.

It is also worth knowing the limits. Gemstones have no stock-market price, dealer margins can be high, and selling takes time. They suit a long horizon and buyers who also enjoy the stones themselves. My role is the stone itself — its quality and its cut — rather than financial advice.

A report first confirms identity: what the stone is, and whether it is natural or synthetic. It records weight, measurements, shape and cutting style. Then comes the part that matters most for value: treatments. The report states, for example, whether a sapphire shows indications of heating, or the degree of clarity enhancement in an emerald.

Many laboratories also give an opinion on geographic origin, such as Burma, Sri Lanka or Colombia. Origin is determined from inclusions and trace elements and is expressed as the laboratory's opinion. Some labs add colour terms such as pigeon's blood or royal blue for stones that meet their criteria.

What a report rarely includes is a cut grade. Coloured stones vary so much in shape that laboratories generally describe the cut rather than grade it. Two stones with identical reports can look completely different on the hand, which is why the quality of the faceting deserves its own attention.

After a recut, the weight and measurements change, so the report should be updated. When I recut or repolish a certified stone, I tell the client in advance and recommend sending it back to the laboratory.

Rough is rarely a tidy shape. Crystals come cracked, waterworn, colour-zoned or full of inclusions. Before I cut, I study the stone under light and magnification and mark what has to go: fractures that would weaken it, inclusions that would show through the table, uneven colour.

Then comes the hardest decision: weight or beauty. A stone cut to keep the most carats is often too deep or too shallow, with a window in the centre or dark areas where light escapes. A stone cut for light gives up weight, but returns brilliance from edge to edge. Where cutting is paid by the carat, weight usually wins.

Orientation matters just as much. Many stones show different colours in different directions, and the finest one sometimes lies along the direction that costs more material. Turning the stone by a few degrees can change the colour of the finished gem.

That is why every gram of dust on my lap is a deliberate decision. What remains is the part of the rough that works best with light.

Many coloured stones were originally cut to keep weight. Typical problems are a window in the centre, where you can see straight through the stone; dark areas called extinction; a lopsided pavilion; or a thick, uneven girdle. Old stones from family jewellery often also have chipped edges and a scratched table after years of wear.

Before I recut, I measure the stone and plan new angles for its material. The aim is to remove as little weight as possible while bringing the light back. A repolish usually costs only a tiny fraction of a carat; a full recut costs more, and how much depends on how far the original cut is from good proportions.

The result is a stone that is lighter on the scale but brighter, livelier and often more beautiful to the eye. Recutting is especially rewarding for sapphires and rubies with large windows, and for stones that are going into a new piece of jewellery.

For certified stones, a recut changes the weight and dimensions, so a new laboratory report is recommended. Before the stone touches the lap, I always discuss the plan and the expected weight loss with you.

It starts with the rough, or with a stone you already own. I study its colour, inclusions and orientation, and ask where it will go: an engagement ring, a pendant, a pair of earrings or a collection. The setting and the way the stone will be worn shape its outline, depth and girdle.

Next, I design the cut. Facet diagrams are planned and checked in gem design software, which traces how light travels through the stone for the material's refractive index. This lets me compare designs before cutting and choose the one that gives the best brilliance, contrast and colour.

You see the plan before I begin: the outline, the expected size and weight, and how the stone should look. Only then does the faceting start. A custom precision cut can follow classic proportions or create something entirely new — a geometric outline, an unusual facet pattern or a cut matched to a specific design.

The result is a gemstone that exists only once, cut with the same precision as the finest traditional cuts. It is the most personal way to work with a stone.

Legend says they were chosen because each one weighed almost the same. In reality the seeds vary quite noticeably — which is exactly why a common standard was eventually needed.

From keration came the Arabic qīrāṭ, the Italian carato and finally the carat. For centuries, though, the unit had no single value: a carat in London, Amsterdam, Lisbon or Florence weighed slightly differently, roughly between 0.19 and 0.21 grams.

The metric carat of exactly 0.2 grams was adopted in 1907 by the General Conference on Weights and Measures and introduced by most countries in the years that followed.

A carat is divided into 100 points, so a 0.50 ct stone weighs 50 points. It measures weight, not size: a carat of dense sapphire is visibly smaller than a carat of lighter quartz or emerald.

Gold has a karat of its own, a measure of purity: 24 karats means pure gold. American English spells it with a K to tell the two apart; in British English both are usually written carat.