Before sitting down to write this piece, we asked a few friends — both casual collectors and diehard enthusiasts — to name the components of a watch. The responses varied little at the start, with all listing movements, hands, dials, indices and crowns as their first five answers. It took until the ninth turn before one flagged the crystal.
Perhaps it’s a good thing that it showed up so late in this exercise. After all, the whole idea of a watch crystal — also known as a watch glass — is to have something that’s practically unnoticeable, being transparent and allowing for good visibility while protecting the components within the case from dust, moisture and shock.
The materials that make up a watch crystal have evolved greatly over the years. As recently as the early 1900s, many pocket watches were encased in rock crystal, a colourless variety of quartz that gave the component its name. When synthetic materials came onto the market in the early 20th century, acrylic became the material of choice as a result of its lightness and durability when compared to quartz.
In the decades that followed, and with the advent of processes such as flame fusion, synthetic sapphire became increasingly popular in watchmaking. The material is prized for its exceptional hardness and resistance to wear. On the Mohs scale of hardness, sapphire sits at a 9, coming in just behind diamond, the hardest naturally occurring material.
Besides the watch crystal, sapphire is also used in movements to reduce friction between moving parts, minimising wear and tear on components such as pivots and gears. Using jewels in movements can thus increase the durability of timepieces while improving accuracy and reliability.
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But not all sapphires are created equal. The methods used to synthesise, shape and polish each crystal have a massive impact on its final qualities. Poor temperature control during the crystal growth process, for example, can lead to uneven texture or even bubbling in the resultant sapphire. Great care, therefore, must be taken to ensure that each sapphire comes out just right.
A step ahead
For Richard Mille, exploring and innovating on the different effects it can create with sapphire has been at the forefront of its watchmaking process.
The maison’s experimentation with sapphire and its potential beyond the watch crystal has been in the works since its founding in 2001. It developed sapphire dial inserts for the first RM 001 and later introduced flat sapphire movement baseplates for the RM 018 Tourbillon Boucheron in 2008.
In 2012, Richard Mille released the RM 056 Tourbillon Split-Seconds Chronograph Sapphire, with its case — comprising the front bezel, caseband and back bezel — rendered in sapphire.
The idea behind this timepiece was sparked during namesake founder Richard Mille’s first viewing of the prototype split-seconds chronograph movement for the RM 050 Felipe Massa. Mille was so enamoured by the movement that he decided the best way to showcase it was to create an entirely clear case.
The RM 056 Tourbillon Split-Seconds Chronograph Sapphire introduced a novel idea in the world of watches: It wasn’t just the front or back of the watch that could be made see-through; by creating a sapphire case, Richard Mille allowed for a clear view into each component of the watch, so the intricacies within could be appreciated from just about every angle.
Creating the case was certainly no easy feat. Sapphire’s hardness, combined with the curved tonneau shape of each case, necessitated new techniques and tools. In total, each case requires more than 1,000 hours of machining, including 350 hours spent on polishing alone. The parts are worked on separately, with dedicated machines used for each.
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The maison’s sapphires — created by Swiss firm Stettler — are synthesised using the Kyropoulos method, which involves heating aluminium oxide to between 2,000°C and 2,050°C in a controlled atmosphere, then allowing the crystal to grow from a seed over up to several weeks.
The Kyropoulos method, developed in 1926 by Spyro Kyropoulos, allows for the growth of larger sapphires than what can typically be achieved with other techniques for sapphire synthesis. With a large block weighing several kilograms needed for each Richard Mille case, this method is the most effective for achieving the maison’s specifications.
Of course, Richard Mille’s innovation didn’t stop with just sapphire cases. The maison soon set to work on using sapphire for other components, such as the tourbillon and centre bridges in the RM 56-01 and RM 56-02.
Kaleidoscope of colours
Richard Mille then expanded into the realm of coloured sapphires, continuing its work with Stettler to create crystals of all hues to be used in its watches. The collaboration culminated in the debut of the RM 07-02 Automatic Sapphire in 2015, with a pink sapphire case.
As with the RM 056 Tourbillon Split-Seconds Chronograph Sapphire, new methods had to be developed to create the new coloured cases.
Synthesising a coloured sapphire involves incorporating dopants into the aluminium oxide crystal structure, with different additions creating different tones. For instance, the most widely known sapphire colour, blue, comes from trace amounts of cobalt; pink sapphires, meanwhile, get their hue from chromium.
It isn’t just a matter of stirring things up and hoping for the best, however. Strict controls on the timing of dopant additions, temperatures and crystal growth rates are needed to ensure the resulting sapphires have the correct hue and that the colouration is consistent — not only within the individual crystal but also across different batches.
In the decade since the original pink model was unveiled, Richard Mille has created numerous new colours of the RM 07-02 Automatic Sapphire, including a number with gem-set cases. Setting gems in sapphire involves another level of precision, with lasers used to drill the holes that will house the stones.
Richard Mille has continued to experiment with sapphire’s potential in watchmaking, pushing the limits of how it can be employed in contemporary haute horology. Most recently, the maison added four new versions to the RM 07-02 Automatic Sapphire collection, including one in a brand-new lilac shade.
Each sapphire-encased creation represents a blend of technical prowess, finesse and ingenuity, in turn changing the way we view watches — literally. Who knew a material prized for being almost invisible would one day come to steal the show?
