It requires the melting in the raw compound using oxyhydrogen flame and also the crystallisation of the melted droplets to variety a cylinder. Graded 9 about the Mohs-hardness scale (graded 1-ten), the resulting sapphire crystals are pretty much scratch-evidence and really really hard, guaranteeing an unhindered vision all the time. https://www.watchesworld.com/the-most-coveted-watches-in-the-uk/