It consists of the melting on the Uncooked compound using oxyhydrogen flame along with the crystallisation in the melted droplets to sort a cylinder. Graded 9 on the Mohs-hardness scale (graded 1-ten), the ensuing sapphire crystals are pretty much scratch-proof and really challenging, ensuring an unhindered eyesight at all times. https://www.watchesworld.com/top-10-dive-watches/