While coloured synthetic sapphires have been in existence since 1902, when they were invented by the French chemist Auguste Victor Louis Verneuil, melting sapphire is a complex and unpredictable process. Because its crystallisation process is unstable, it is difficult to obtain similarly coloured sapphires, even if they are produced simultaneously. Furthermore, bubbles and cracks can appear in the material, making the end result unsuitable for producing Big Bang cases. But the main challenge is in the size. Thus far, no coloured sapphires exceeding 2 kg have been produced. However, Hublot has now gone beyond this threshold. By pushing the limits of engineering and chemistry, it has developed a sophisticated and costly process that has resulted in the successful production of a large, transparent sapphire of perfectly uniform colour. Hublot heats aluminium oxide (Al2O3) — the raw material for sapphire — with a transition metal, chromium (Cr), at a temperature of between 2000 and 2050 degrees Celsius. The result is a coloured sapphire that retains all the original properties of a material which is ultra-scratch resistant, completely transparent and among the hardest in existence. The innovation extends to the colour — the first blue sapphire in the history of watchmaking.
The case middle, the bezel and the case back of the Big Bang Unico Sapphire are cut from blocks of blue coloured sapphire. Flange, indices, Arabic numerals and hour/minute hands toned to match the colour of the sapphire, through contrast revealing the mechanism of the Unico HUB124 proprietary movement and its column wheel on the dial side.