Crystal Clear – Explaining Why Sapphire Is Used In Watchmaking

Cultural Perspectives • 16 Dec 2016

Crystal Clear – Explaining Why Sapphire Is Used In Watchmaking

by Victor Toth

Watch lovers and collectors eager to appreciate the fine details of the mechanics inside their watches had to wait a very long time indeed for transparent case backs – which are usually sapphire crystal – to become commonplace. Today, let us discover the latest and greatest of wholly translucent timepieces and the technical wonders that allow us to see high-end watches like we have never seen before.

Sapphire crystal, hard, transparent and stable, has for ages been the de facto material for transparent front and rear crystals in high-end timepieces. And yet, for reasons we shall soon discover, watches with cases entirely in sapphire were not to be until just a few years ago.

To understand the reasons behind the development of sapphire in watchmaking, let us briefly familiarize ourselves with the material itself, which is also known as corundum.

Corundum is a crystalline form of aluminum oxide (Al2O3), typically containing traces of iron, titanium, vanadium and chromium. It is a naturally transparent material, but can have different colours when impurities are present. Transparent specimens are used as gems, being rubies if red and padparadscha sapphires if pink-orange. All other colours, as well as fully transparent forms, sapphire, with a prefix denoting the colour, for example “green sapphire” for a green specimen.

What really matters for watch manufacturers and collectors alike is the Grade 9 hardness of sapphire crystal on the Mohs-hardness scale. Graduated on a scale of 1 to 10, the Mohs-hardness scale measures surface hardness, meaning sapphire is amongst the hardest materials on Earth. It’s hard enough to scratch any other material that ranks below it on the scale – and, inversely, can only be scratched by materials that rank above it, which is only diamond.

Because sapphire is essentially scratch-proof, it is the ideal material for watch crystals, especially on the front. The crystal occupies the most real estate on the face of the watch, making it the most vulnerable to accidental knocks and scrapes.

The issue when it comes to working with sapphire is that though it is very stable in finished form, sapphire is extremely prone to cracking and shattering when being machined, cut or processed. This explains why for decades the front and rear crystals on watches were most simple geometric shapes – that is to say round or rectangular – and it was only a couple of years ago that crystal shapes started to becoming more diverse, and even other watch case elements began to be crafted from the material.

One of the pioneers in using the material was MB&F for its Horological Machine 2 SV (or HM2-SV), a watch that featured a very complex front plate crafted from sapphire.

It was as recently as 2012 when Richard Mille and Cecil Purnell have both debuted what are believed to be the first sapphire cased watches. Called the Cecil Purnell Mirage and Richard Mille RM 056, it was of course the latter that really stole the show – and, to be fair, also the one that was actually made in more than one piece.

Cecil Purnell Mirage

Cecil Purnell Mirage


Since its 2012 debut, Richard Mille has produced a few other iterations of sapphire cased watches, always in extremely limited quantities and with seven-figure price tags.

Richard Mille RM 056

Richard Mille RM 056


Richard Mille claims that the case of the RM 056 takes a total of 1000 hours to machine, which, even if craftsmen and machines work 168 hours a week, takes one and a half months to complete. If any part were to crack during in the manufacturing process, the component has to be thrown away, and with it all the time and energy that went into its production. And then the production process would have to start from scratch, with the 1000 hours required starting anew.

The latest brand to join the sapphire craze was Hublot with the Hublot Big Bang Unico Sapphire and its two iterations: one completely clear and transparent while the other being the ”All Black” version with black tinted sapphire case band and back and also bezel.

Regardless of its color, the Unico Sapphire comes in at a fraction of the price of the aforementioned pieces, making it a very interesting and well-timed alternative, while also offering a most comparable visual wow-factor. As is always the case with unusual high-end timepieces, these sapphire-cased horological outlaws need to be seen in the flesh to be fully appreciated.

Hublot Big Bang Unico Sapphire

Hublot Big Bang Unico Sapphire


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Tags: hour glass hour glass singapore hublot hublot singapore hublot watch hublot watch singapore the hour glass

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