It requires the melting with the raw substance making use of oxyhydrogen flame and also the crystallisation in the melted droplets to type a cylinder. Graded 9 on the Mohs-hardness scale (graded 1-10), the ensuing sapphire crystals are virtually scratch-evidence and very challenging, ensuring an unhindered eyesight all the time. https://www.watchesworld.com/top-10-dive-watches/