It requires the melting of the Uncooked material applying oxyhydrogen flame and the crystallisation with the melted droplets to sort a cylinder. Graded nine around the Mohs-hardness scale (graded one-ten), the resulting sapphire crystals are virtually scratch-proof and very really hard, making certain an unhindered eyesight all of the time. https://www.watchesworld.com/top-10-dive-watches/