It entails the melting on the raw material employing oxyhydrogen flame as well as crystallisation on the melted droplets to kind a cylinder. Graded 9 around the Mohs-hardness scale (graded one-ten), the resulting sapphire crystals are practically scratch-evidence and very tough, making certain an unhindered vision always. Useful cookies Useful https://www.watchesworld.com/top-10-dive-watches/