It consists of the melting of the Uncooked material working with oxyhydrogen flame and the crystallisation of the melted droplets to kind a cylinder. Graded 9 on the Mohs-hardness scale (graded 1-10), the ensuing sapphire crystals are practically scratch-evidence and really hard, guaranteeing an unhindered vision always. Useful cookies Functional https://www.watchesworld.com/top-10-dive-watches/