It involves the melting from the raw compound utilizing oxyhydrogen flame along with the crystallisation in the melted droplets to type a cylinder. Graded nine to the Mohs-hardness scale (graded 1-10), the ensuing sapphire crystals are practically scratch-proof and really really hard, making certain an unhindered vision all the time. https://www.watchesworld.com/top-10-dive-watches/