It involves the melting of the raw compound using oxyhydrogen flame plus the crystallisation of your melted droplets to sort a cylinder. Graded nine around the Mohs-hardness scale (graded one-10), the resulting sapphire crystals are pretty much scratch-evidence and very difficult, guaranteeing an unhindered vision continually. Particularly practical for divers https://www.watchesworld.com/top-10-dive-watches/