It will involve the melting from the raw compound applying oxyhydrogen flame as well as crystallisation on the melted droplets to form a cylinder. Graded nine on the Mohs-hardness scale (graded 1-ten), the ensuing sapphire crystals are practically scratch-evidence and very hard, making sure an unhindered vision all the time. https://www.watchesworld.com/top-10-dive-watches/