It involves the melting of the raw substance employing oxyhydrogen flame along with the crystallisation on the melted droplets to sort a cylinder. Graded 9 within the Mohs-hardness scale (graded 1-ten), the resulting sapphire crystals are practically scratch-evidence and very challenging, guaranteeing an unhindered vision continually. Purposeful cookies Useful cookies https://www.watchesworld.com/top-10-dive-watches/