It involves the melting on the raw material using oxyhydrogen flame as well as the crystallisation on the melted droplets to variety a cylinder. Graded 9 within the Mohs-hardness scale (graded one-ten), the ensuing sapphire crystals are pretty much scratch-proof and very difficult, guaranteeing an unhindered vision constantly. Useful cookies https://www.watchesworld.com/top-10-dive-watches/