It requires the melting in the Uncooked material applying oxyhydrogen flame as well as crystallisation with the melted droplets to kind a cylinder. Graded 9 to the Mohs-hardness scale (graded 1-10), the resulting sapphire crystals are just about scratch-proof and really difficult, making certain an unhindered vision at all times. https://www.watchesworld.com/top-10-dive-watches/