It will involve the melting of your raw compound using oxyhydrogen flame as well as the crystallisation of your melted droplets to type a cylinder. Graded 9 about the Mohs-hardness scale (graded 1-ten), the ensuing sapphire crystals are almost scratch-evidence and really tough, ensuring an unhindered vision all the time. https://www.watchesworld.com/top-10-dive-watches/