It consists of the melting of the raw substance using oxyhydrogen flame and the crystallisation on the melted droplets to form a cylinder. Graded nine within the Mohs-hardness scale (graded one-ten), the resulting sapphire crystals are just about scratch-proof and very hard, making certain an unhindered eyesight all the time. https://www.watchesworld.com/top-10-dive-watches/