It requires the melting from the raw compound applying oxyhydrogen flame along with the crystallisation in the melted droplets to type a cylinder. Graded 9 to the Mohs-hardness scale (graded one-ten), the ensuing sapphire crystals are pretty much scratch-evidence and really difficult, ensuring an unhindered vision all the time. The https://www.watchesworld.com/top-10-dive-watches/