It requires the melting of the Uncooked material using oxyhydrogen flame plus the crystallisation from the melted droplets to form a cylinder. Graded 9 over the Mohs-hardness scale (graded 1-ten), the ensuing sapphire crystals are practically scratch-evidence and really really hard, ensuring an unhindered eyesight all of the time. Later https://www.watchesworld.com/top-10-dive-watches/