It involves the melting of the Uncooked compound working with oxyhydrogen flame and the crystallisation of the melted droplets to kind a cylinder. Graded 9 over the Mohs-hardness scale (graded 1-10), the resulting sapphire crystals are almost scratch-evidence and very challenging, making certain an unhindered vision all of the time. https://www.watchesworld.com/top-10-dive-watches/