It involves the melting on the raw substance utilizing oxyhydrogen flame along with the crystallisation of the melted droplets to sort a cylinder. Graded 9 around the Mohs-hardness scale (graded one-ten), the resulting sapphire crystals are pretty much scratch-evidence and very tricky, ensuring an unhindered eyesight all of the time. https://www.watchesworld.com/top-10-dive-watches/