It consists of the melting from the raw material applying oxyhydrogen flame and the crystallisation of the melted droplets to sort a cylinder. Graded 9 within the Mohs-hardness scale (graded 1-10), the ensuing sapphire crystals are pretty much scratch-proof and really challenging, guaranteeing an unhindered eyesight all of the time. https://www.watchesworld.com/top-10-dive-watches/