It requires the melting with the raw compound applying oxyhydrogen flame as well as the crystallisation in the melted droplets to kind a cylinder. Graded nine around the Mohs-hardness scale (graded one-ten), the ensuing sapphire crystals are nearly scratch-evidence and really tough, making sure an unhindered eyesight all the time. https://www.watchesworld.com/top-10-dive-watches/