It requires the melting of the raw substance utilizing oxyhydrogen flame along with the crystallisation on the melted droplets to type a cylinder. Graded 9 over the Mohs-hardness scale (graded 1-10), the resulting sapphire crystals are just about scratch-evidence and very hard, ensuring an unhindered eyesight all of the time. https://www.watchesworld.com/top-10-dive-watches/