It consists of the melting from the raw material applying oxyhydrogen flame as well as crystallisation from the melted droplets to sort a cylinder. Graded nine about the Mohs-hardness scale (graded one-ten), the ensuing sapphire crystals are pretty much scratch-proof and really difficult, guaranteeing an unhindered vision at all times. https://www.watchesworld.com/top-10-dive-watches/