It consists of the melting of the raw material working with oxyhydrogen flame as well as crystallisation with the melted droplets to form a cylinder. Graded 9 about the Mohs-hardness scale (graded 1-ten), the resulting sapphire crystals are pretty much scratch-evidence and very hard, making certain an unhindered vision constantly. https://www.watchesworld.com/top-10-dive-watches/