The skill required to set a watch with gemstones has long been overlooked in the hierarchy of horological abilities. With gem-set watches experiencing greater heights of popularity – and creativity – than ever, it’s time we reappraised this unfairly overlooked corner of watchmaking craft.

Western Europe, which is still watchmaking’s cultural lodestar, despite the industry’s global appeal, has historically had a rather narrow view of gem-set watches. They are for women, for celebrities, the gauche “new money” sorts – small-minded views that now seem of a distant time. (Read up on how attitudes changed here.) For a long while, they were the sole preserve of after-market customisation, something deemed rather infra dig by Geneva’s legacy brands. Men of taste are supposedly meant to showcase their horological discernment through elegant complications such as tourbillons, perpetual calendars and, for the truly cultured, an equation of time.

Everywhere else, however, a bezel flush with baguettes or a dial randomly snow-scattered with diamonds is a sign of appreciation for an art form that requires as much skill as fashioning a tourbillon. Gem setting is a complication in its own right and one that, if you want to read anything into Patek Philippe’s recent investment in renowned gem-setter Mr Pierre Salanitro’s business (the man who sets for everyone, from Richemont to Rolex), is well and truly back in fashion.

The art of gem setting watches dates back much further than you might think. All the way back, in fact, to the 16th-century protestant revolution. In 1558, reformation church leader Mr John Calvin enacted a ban on ostentatious jewellery and clothing in Switzerland that saw pocket watches being set with precious stones because of an exemption for mechanical objects. It was gem-setting as unnecessary frippery, decoration without function, and it lasted for centuries.

The vogue for utilitarian styles in the 1940s and 1950s saw this metier d’art all but die out, except for women’s cocktail watches or jewellery-influenced pieces. However, technological advances as well as changing tastes saw precious-stone watches making a comeback in the early 2000s and not just on delicate jewellery styles either. Today, even the most ostensibly sporty or practical designs – such as a Rolex GMT-Master II or Omega Speedmaster – are found with glittering rings of diamond, ruby and sapphire.

The first challenge is choosing the stones. For watches, only three of the four Cs apply. The four Cs are the qualities that are assessed before grading a diamond established by the Gemmological Institute of America (GIA) and introduced to the general public by De Beers. In no particular order, they are: colour, the whiter the better; cut, how it has been faceted by the cutter; clarity, how many flaws it has; and carat, or how big it is. Watches are generally set with small stones, so it’s the accumulative carat that is important, not the weight of a single stone. The definition of cut is also expanded to include the actual shape of the stone. And for this, it depends what area of the watch is being set.

Baguettes and brilliants are the most common shapes, but some brands such as Graff and Vacheron Constantin have their stones cut into unique shapes, such as triangles and flames. A brilliant is a round cut, invented in 1919 by Mr Marcel Tolkowsky and designed to increase the amount of refracted light, or fire, a stone could produce. Side on, it has a lower pointed pavilion, upper crown and flat top called a table. The pavilion and the crown are faceted or cut into flat surfaces. In order to ensure 100 per cent of the light is internally reflected to the opposite side of the pavilion and then returned to the eye, the corner angles of the pavilion must be 43 degrees. If it is shallower or deeper, light leaks out of the back of the stone dulling its brilliance.

Baguettes have less fire, due to their meagre 14 facets compared to a brilliant’s 58, however they are ideal for bezel setting. While jewellery tends to use straight-sided baguettes, the ones for watches are re-cut into tapered shape, so that, when placed side by side, they start to form a circle. Setting watch cases and bracelets usually requires a mix of brilliant and baguette-cut stones, depending on the shapes involved. Both cuts are also frequently used on dials in place of traditional hour markers.

To pavé set a dial – so named because the area is literally paved with diamonds – you need miniscule stones of the same size and shape. This is where melee diamonds, stones under 0.15ct, come in. These aren’t chips or off-cuts from larger stones but are shaped and hand-polished stones in their own right. Substantial stones may make the headlines, but it is melee ones that make up the larger proportion of the world’s diamond market. Companies such as Antwerp-based Dimexon use microscopes to cut its calibrated smalls – stones sized from 0.06-4mm – to within a 0.05mm tolerance; stones which are then polished, certified, and tracked to ensure peace of mind.

Some brands use stones in other, distinctive ways: Cartier is famous for including a “cabochon”, a smooth, domed precious stone, set into the crown of every watch. Usually a blue sapphire, but on platinum watches it is replaced with a ruby, and on rare occasions can be other colours.

In recent years, other watchmakers have begun to experiment with synthetic diamonds, which offers unprecedented flexibility in terms of the cut on offer. TAG Heuer’s Carrera Plasma, for example, has a solid diamond crown and a medley of irregular, jagged lab-grown diamonds set directly into its aluminium.

How you set says just as much as what you set. The simplest way of securing a stone is with a collar of metal known as a bezel. The next skill level is the claw with metal prongs used to hold the stones in place. Invisible setting – where no metal holding the stone in place is visible from any angle, requiring the stones to have small grooves cut into their underside that marry up with ridges in the metal below – is one of the most visually spectacular and hardest to achieve.

In general, pavé setting is the most common, providing that wall-to-wall, “iced-out” effect, but it is not without substantial risk to the integrity of the watch. Holes are drilled or carved into the case, bracelet or dial to create a perfect space into which the stone can nestle. Taking metal away from a case weakens its structural integrity, something that is further exacerbated on ultra-thin and skeletonised styles such as Piaget’s Altiplano.

“We have found a few tricks to successfully set stones on or skeleton movements,” says Mr Rémi Jomard, product designer and innovator at Piaget. “We always bend ourselves to adapt to what the design requires.”

Adapting also means knowing the unique qualities of the material you are working with. Because gem setting was originally associated with dress watches, watchmakers have traditionally set into gold, which is soft and therefore quite forgiving. However, the move that modern brands have made towards high-tech materials has given setters the challenge of trying to insert stones in everything from titanium to carbon fibre – see Hublot’s Big Bang and Spirit of Big Bang collections.

“It all depends on the level of expertise of the gemsetter,” says Mr Guillaume Chautru, head of gemmology at Piaget, when asked if there are certain stones or metals that don’t mix. “Here, anything is possible. We can set sub-millimeter sapphires with titanium claws or slices of malachite that are 0.8mm thin. When you know how delicate and soft malachite is, it’s a real challenge. And to be fair, before joining Piaget I never thought that would be possible.”

Mr Federico Ziviani, general manager at Gerald Charles, takes a more circumspect approach, acknowledging that the shape of the case as well as the stone you use can bring different challenges.

“The Gerald Charles Maestro case is a challenge to work with,” Ziviani says. “Not much because of the material in itself, but rather for the complex shapes: it has no straight lines in its construction so once again there’s no regular surface to work on.

“To achieve the results we want, all the elements must be perfectly engineered. The gemstones must be of a good size and quality, a perfect cut and polishing, the map must be perfectly studied to have the perfect position of each diamond on the watch, the metal must be well cut and polished under the stone, the prongs must be minimal but strong and polished. Stone set watches are a work of art, and the Maestro makes no exception.”

Gerald Charles also likes to throw in the extra challenge of using rubies and emeralds, which are not as hard as diamonds and makes setting them without damage even more taxing. “Stones like rubies or emeralds are more fragile than diamonds, requiring extra care when worn, but exceptional care when set,” Ziviani says. “If a diamond can tolerate the excess of force exerted by the master setter, other ‘softer’ stones cannot, and can be easily cracked.”

The only definitive is that gem setting is always a conversation between the gemologist and the designer. As Rolex explains, “A gem-setter’s craft is multi-faceted. First, decisions are made with designers in the creation division about the colours and arrangement of the stones. This is a subtle exercise in finding a balance between aesthetic and technical requirements. Then follows a consultation with the case and bracelet engineers. Together they study the future placement of the stones in order to prepare, to the nearest micron, the gold or platinum into which the stones will be set. For each stone, they determine the precise amount of metal required to hold it in place.”

Or to use Jomard’s succinct summation, “Technique has to serve the aesthetic.”

The trend that has done more than any other to cement gemsetting’s complication status is the rainbow setting. As the name suggests, this uses precious stones to chart the tonal shifts of colour in a rainbow, either around the bezel or gradated through the dial. Rolex has been the early adopter with its Daytona ref 116598RBOW and ref 116599RBOW kick-starting things back in 2012, though it was rainbow setting the octagonal bezel of its Cellini as far back as the 1980s.

Today, brands from Hublot and Patek Philippe to Omega and Audemars Piguet are committed rainbow-heads. But, for many, Rolex is the pinnacle partly because of the astounding lengths it goes to with its stones.

To achieve these levels of vibrancy in sapphires heat treatment is normally used. Rolex sources all-natural stones, then cuts them to size with 90 per cent of each coloured stone being discarded in order to achieve the perfect gradient. Sure, it doesn’t help with accuracy or reduce friction, but it takes a unique level of skill. And isn’t that what complicated watchmaking it’s all about?